Servo Magazine 03 2005

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Circle #27 onthe Reader Service Card.

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Features & Projects

On The Cover

SERVO Magazine (ISSN 1546-0592/CDN Pub Agree#40702530) is published monthly for $24.95 per year by T & L Publications, Inc., 430Princeland Court, Corona, CA 92879. APPLICATION TO MAIL AT PERIODICALS POSTAGE RATE IS PENDING AT CORONA, CA AND ATADDITIONAL ENTRY MAILING OFFICES. POSTMASTER: Send address changes to SERVO Magazine, 430 Princeland Court,Corona, CA 92879-1300 or Station A, P.O. Box 54,Windsor ON N9A 6J5; [email protected]

SERVO2266 Inside the Iron Man

Carlos Owens’ 18-Foot Mecha Giant

3300 The Mini Servo WalkerPart 1: The Construction of a Hex Walker

3355 Eastern Canadian Robot GamesEighty Robots Compete for the Gold

3399 R2-D2: A PC-Powered RobotBring the Movie into Your Living Room

4477 Robosapien2, Bigger Than Ever Introducing the New Model and Some Friends

5511 Reusable Robot SoftwarePart 2: Localization and Odometry

7766 Zoë on the Atacama DesertTraining Robots for Other Worlds

8822 The Heath HERO RobotLooking Back at a Popular Robot

2266

7766

3300

Bounding onto the cover thismonth is Robopet, one ofWowWee’s latest creations.Photo courtesy WowWee, Ltd.

This Page: A night shot of theAtacama campground. Photo courtesy Carnegie-Mellon

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ColumnsDepar tments

3.2005VOL. 3 NO. 3

6 Mind/IronThe R2-D2 Effect

7 Bio-FeedbackWhere You Have a Voice

18 Events CalendarFind a Show Near You

19 Robotics ShowcaseGet What You Need Quick

20 Brain MatrixServos

44 New ProductsThe Latest Project Parts

46 Robo-LinksYour Link to Parts and Services

58 SERVO BookstoreFeed Your Brain

73 MenagerieROBOlympics are Coming Soon

81 Advertiser’s IndexA List of Supporting Advertisers

8 RubberbandsWhen Robots Talk Back

12 Ask Mr. RobotoYour Problems Solved Here

22 Twin TweaksTweaking the Land Sea 2 R/C

60 GeerHeadSix-Legged Forest Walker

65 RobytesNews from the Robotics World

67 Robotics ResourcesFramework for Your Robot

80 AppetizerSo You Want to Build Robots?

Coming 4.2005Neural Networks 101Stephen L. Thaler, Ph.D., presidentand CEO of Imagination Engines,Inc., introduces the complex concepts of neural networks capable of human-level discoveryand invention. He describes the“mental” structures needed to create neural networks and theirpower.

If every tool, when ordered, or even of its own accord,could do the work that befits it ... then there would be no

need of apprentices for the master, workers, or of slaves forthe lords. — Aristotle, 322 B.C.

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Published Monthly By The TechTrax Group — A Division Of

T & L Publications, Inc.430 Princeland Court

Corona, CA 92879-1300(951) 371-8497

FAX (951) 371-3052www.servomagazine.com

Subscription Order ONLY Line1-800-783-4624

PUBLISHERLarry Lemieux

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ASSOCIATE PUBLISHER/VP OF SALES/MARKETING

Robin [email protected]

EDITORRyan Lee Price

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MANAGING EDITORAlexandra Lindstrom

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CIRCULATION DIRECTORMary Descaro

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WEB CONTENT/STOREMichael Kaudze

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PRODUCTION/GRAPHICSShannon Lemieux

STAFFDawn SaladinoCorrie PanzerKristin Rutz

OUR PET ROBOTSGuidoMifune

Copyright 2005 by T & L Publications, Inc.

All Rights Reserved

All advertising is subject to publisher's approval.We are not responsible for mistakes, misprints,or typographical errors. SERVO Magazineassumes no responsibility for the availability orcondition of advertised items or for the honestyof the advertiser.The publisher makes no claimsfor the legality of any item advertised in SERVO.This is the sole responsibility of the advertiser.Advertisers and their agencies agree toindemnify and protect the publisher from anyand all claims, action, or expense arising fromadvertising placed in SERVO. Please send allsubscription orders, correspondence, UPS,overnight mail, and artwork to: 430 PrincelandCourt, Corona, CA 92879.

If you were to ask any average person toname a robot, any robot, invariably theywould rattle off the likes of R2-D2 and

C-3P0 with minimal difficulty. That’sunderstandable. They’re the world’s mostpopular robotic duo, but — along withRobby the Robot from Forbidden Planet andthe “Lost in Space” robot, B-9 — theyrepresent the exception to the understandingthat robots are generally portrayed asantagonists in the movies and on TV.

Given the amount of evil robots asadversaries in mainstream films, it reallycomes as no surprise why the majority ofpeople see robots as antagonistic charactersthat are constantly altering their directives,changing their programs, and disobeyingtheir primary functions to enable themselvesto do what we'd expect about 35 minutesinto the film: resent and then try to destroyall of mankind. Popular entertainment isdriven by conflict, struggle, and adversity.You'd be bored to tears if you sat throughtwo hours of a movie without the drama ofgood versus evil.

Sure, there are plenty of good robotsout there (V.I.N.CENT and Bob, those twolovable trash cans from The Black Hole, theannoying Johnny 5 from Short Circuit,Andrew from Bicentennial Man, and thoselittle service robots from Silent Running:Huey, Duey, and Luey). If we wanted tostretch it to television, we could even includeKITT from “Knight Rider,” Data from “StarTrek,” and bumbling Twiki from “BuckRodgers.”

The vast number of these good robotsaren't plot drivers (Bicentennial Manexcluded); they don't create the centraldrama of a movie or TV show. The goodnessof R2-D2 didn't convince Luke to fight thedark side (he only brought the message, towhich Luke replied, "sorry, wrong number"),and KITT never caused a crooked sheriff totrick an old lady out of her land. He was

mostly transportation with know-it-alloptional features that caused a lot offantastic sparks. The evil robots are wherewe find the conflict and drama that drivepeople to the movies.

HAL (though not really a robot, onecould argue that he was autonomously thewhole ship), on the other hand, caused theconflict in 2001 and had to be stopped. Thefirst ever robot to grace the silver screen —Maria from Metropolis — is a prime example.Guess what happened after robot Mariareceived the soul from the human Maria?Yep, she turned evil, showing us that robotsare not designed to handle human feelings,and they revert to the lowest form ofemotion when forced to. Singing cowboyGene Autry fought the evil robot army ofQueen Tika in Phantom Empire, while 20years later we watched “Gort” decide thefate of mankind in The Day the Earth StoodStill.

Fast forwarding to a more modern era,the opinion hasn't much changed. Mostnotable in this group are: Ash in Alien —who killed most of the crew (as opposed toBishop in Aliens who saved only some of thecrew), the Cylons, Roy Batty, Leon, Pris andRachael Rosen — the murderous lot fromBlade Runner, Enforcement Droid 209 inRoboCop, all of the robots except Sonny iniRobot, and the list goes on.

These robots controlled the outcome ofthe movies they were in because they werethe central conflicts and the sources of themain characters’ motivation: destroy therobot before the robot destroys me.

The more robots that come intocommon usage and become accepted asthe tools, teammates, pets, and friends wewant them to be, the less we'll have towatch a movie about a horde of themdescending on a small village of innocentpeople. I mean, when is the last time yousaw a movie about a hair dryer? SV

6 SERVO 03.2005

Mind / Iron

by Ryan Lee Price

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7

Up the AnteI enjoy the magazine, but keep

wishing for articles with moresubstance. I would like to see somearticles that go the next step beyondjust motorizing a platform with one ortwo sensors. This has been doneseveral times, but I find that readingabout what other people have done tocompete in a competition shows moreof the real word issues.

The Trinity Fire Fighting contest isa good challenge. How about justtaking one of the less trivialrequirements and assisting the readerin solving it or seeing multiplesolutions for them. We don’t evenneed to solve them, just discussing theproblems helps. The differencebetween reading a university researchpaper and wanting to try an idea theydiscuss and what SERVO discusses islike the Grand Canyon. Yet, I don’tthink they are really that far ahead ofthe amateur robotics person, exceptmaybe in funding. I would like to seeSERVO fill this gap and still embracethe new person if at all possible.

Jeff Dunkervia Internet

As the new editor, Jeff, one of myideas for future issues is to print moreprojects about purpose-built robotsthat show the reader a real-lifeapplication and how it might apply tosomething you’re building at home.There are thousands of roboteers outthere who are building some amazingthings. My job is to bring them to you.

— Editor

Some SERVO Suggestions Please do an article on

accelerometers. I am looking at atrotting robot design that will need a

three-axis feedback on the position ofthe body in mid-air. If there areaccelerometer boards available thatare easy to connect to a servopod,that connection information would behandy. Low-cost accelerometersmeasure two g-forces. What if myrobot generates four g-forces?

How about adding a searchfunction on the website to searchtopics in past issues? My Internetconnection is 26.4 kps. Broadband isnot available where I live. Some ofyour web pages take a long time todownload. Can you lighten them?

Dennis Evansvia Internet

Dennis, we’re sorry to hear aboutyour slow Internet connection speed,but in order to read the content onsome of the pages of our website, ithas to be a certain size.

To answer your question, SignalQuest in Lebanon, NH(www.signalquest. com), offers theSQ-XL-DAQ line of accelerometerswith digital serial output. Using aserial interface cable, it can functionas a self-contained data acquisitionsystem for two- or three-axisacceleration, tilt, and vibrationmeasurements, with models availablefor ±1.5 to ±50 g-forces.

Complete the ProjectsSERVO is a very nice magazine. I

believe that a balance between how-to and team reporting would serve thegeneral robotic builder better. A seriesof articles that step the builderthrough the construction of a driveplatform, controls, software, etc.,would gain more interest.

George Jonesvia Internet

In future months, George, youwill see SERVO not only as a source ofentertainment, but as a guide to thefuture of building robots andautomation for the beginner and theadvanced alike. — Editor

Great Job, SERVOIt is great to see a magazine like

this finally hitting the stands on aregular basis and packed with so manygood articles spanning the world ofpersonal robotics! I enjoy reading yourmagazine and seeing what othergroups and individuals have workedon! Keep up the good work!

Forrestvia Internet

Thank you very much, Forrest. Weare happy that you are satisfied withthe magazine.

SERVO 03.2005 7

Calling all Robots!Attention roboteers! We want to hear from you!

Do you have a great bot that you would like to sharewith the world? We’re looking for anything from sumosto line followers to multi-servo robotic arms. Send us acouple of pictures of your latest project, and we’ll behappy to show it off in our “Menagerie” department.Don’t forget to include a few words about how you builtit and what went into it. For prints, send them to:SERVO Menagerie, 430 Princeland Court, Corona,CA, 92879; for digital images, email them [email protected]

Contact UsIf you have general questions orcomments about SERVO Magazine,please contact us: SERVO Bio-Feedback,430 Princeland Court, Corona, CA 92879;or email: [email protected]

JanPages6&7.qxd 2/2/2005 3:24 PM Page 7

8 SERVO 03.2005

You already have learned how to give your robot the abilityto communicate with you by using a text-based LCD display

and by generating sounds of its own. This column will raisethe bar a little higher yet by showing how you can give yourrobot a voice so that it can simply tell you something insteadof requiring you to read a display or interpret a set of tones.This might sound like it would be a difficult task, but — in reality— it is quite easy. With just a little bit of work, you can havea remarkably natural-sounding voice that far exceeds the qual-ity of other voice generators that were previously available.

You may be familiar with a company called Winbond. Afew years ago, they purchased a company called ISD, whichproduced a series of analog EEPROM devices that allowedyou to record varying lengths of audio onto the chip for laterplayback. Winbond continues to produce these chips, but hasstarted to branch off of that idea and is now producing otherinteresting audio products, such as chips that can play MIDImusic and chips that allow you to convert text input intospeech. There is a company called Grand Idea Studios that

took Winbond’s chip and packaged it into a very easy-to-useproduct that they are now selling through Parallax, Inc.(www.parallax.com).

In the past, other speech processors have had some pretty terrible output. If you trained your ear, you couldunderstand the words that they were saying, but if you wereencountering a device that used those chips for the first time,you likely wouldn’t understand what they were saying.

That is not the case now. With the Emic Text-to-Speech Module, you have a clearly

intelligible woman’s voice that is only slightly synthetic-soundingdue to the lack of pitch and speed variations that people usewhile speaking. Winbond has an interactive demo of whattheir chip sounds like on their website. You can find thisdemo at www.winbond-usa.com/ttsdemo/

Let’s Make It WorkWhen you order the Emic Text-to-Speech Module, it will

by Jack Buffingtonby Jack Buffington

When Robots Talk Back:A Simple Way to Add Speech

Capability to Your Robot

Figure 1. Pinout for the Emic Text-to-Speech Module.

Figure 2. Connection between the Emic module and a PIC.

Rubberbands.qxd 1/28/2005 4:42 PM Page 8

arrive as a single inline pin package that you can fit into anyprototyping board that has 0.1-inch spacing. You only needto connect four of the pins to your microprocessor. Carefulexperimentation with the timing of how you send your commands would allow you to reduce this down to just one.You can connect a speaker directly to the circuit board andhear the speech at a reasonable level. If you want it to belouder, though, the board has a special pin that you can connect to an external amplifier. The Emic board runs at fivevolts, so you will need an external regulator to power it. Thatshouldn’t be a problem, since you will likely be using onealready for your microprocessor.

Figure 1 shows the pinout for the Emic module. Figure 2shows how the module can be connected to a PIC microcon-troller. The Emic’s serial lines communicate at 2400 baud.Communication with the Emic module can be done throughtwo different methods. The first method uses single bytecommands to tell the module what you want to do. Theother method uses ASCII commands. In this column, we willuse the second method because it is more straightforward. Ifyou are limited in program space or processor time, youmight opt for the first method.

Let’s go over the function of each of the four pins thatyou need to connect to. The /RESET pin allows you to do ahard reset on the Emic module. This will clear all settings andreset the board to its initial start-up state. In normal use, youwill drive this pin high to activate the module. Going upward,the next pin in Figure 1 is the BUSY pin. This pin is almostself-explanatory. When the Emic module is busy processing acommand, it will raise this pin high. This pin does not instant-ly go high after you send a command, so you will need towait up to a millisecond after sending your commands beforechecking this pin’s state. Since it takes a varying amount oftime to speak each sentence or processeach command that you send to theEmic module, it is a good idea to checkthis pin to see if the module is ready toaccept new commands.

At the top of the module is theSerial In pin. You will be sending your commands to this pin in RS232serial format, except that you will beusing zero to five volt levels instead of±12 volts. All commands are sent at2400 baud. There are two dipswitcheson the Emic module. The switchlabeled “1” allows you to select ASCII or hexidecimal commands. Themethod described here will use ASCIIcommands, so set this switch to on.Switch “2” allows you to choose (if youwant) the module to echo bytes sent toit back to the host processor. Thiswon’t be necessary for this application,so set this switch to the off position.

There are four main commands

that you will want to know when using the Emic module. Thefirst — and most important — is the “say” command. If, forexample, you sent the string “say=I’ve been a bad robot!;” tothe Emic module, it would faithfully speak that sentence.Anything after the equals sign will be said. Notice that there isa semicolon following the sentence. This semicolon tells theEmic module that you have finished sending a command. If youdon’t send the semicolon, the Emic module will remain silent.

The next command that you will want to know is the vol-ume command, as there are eight volume levels. They rangefrom zero to seven. The default level is Level Four, while zerosets the volume to be fully off. To change the volume to LevelSix you would send “volume=6;”. Notice that a semicolononce again followed the command. The Emic module can bedirectly connected to a speaker, as was shown in Figure 2,but the volume level is only suitable for a device that will beused in a relatively quiet location when you do this. If youneed additional volume, then you could connect an externalamplifier — such as the LM386 — to the AOUT pin.

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There are two commands that allow you to change theway that the Emic module sounds. These are the “speed=”and “pitch=” commands. The speed command has a rangefrom zero to four and has a default of two. The pitch command has a range of zero to six and its default is one. Ingeneral, you will want to leave these settings alone, since themodule sounds best at the defaults. For some situations,though, you may prefer to play around with these to achievebetter results for your application.

For the volume, pitch, and speed commands, you canopt to send “+” or “-“ instead of a specific level. The Emicmodule will take care of adjusting the values for you and willnot let them go above or below their limits. An example ofthis would be “speed=+;”.

Figure 3 shows a program fragment that will endlesslycause the Emic module to repeat a stupid joke over and over.It should be pretty clear from this example that addingspeech to your robot is almost a no-brainer, and it’s too badthat everything in robotics isn’t this easy!

The final pin that you may want to use is the Serial Outpin. This pin will output “OK” after each section of text thatyou send to it to speak. This pin also allows you to communi-cate with the Emic module using other commands that allowyou to do things like create abbreviations for words. Youmight, for example, send “TTYL” instead of “talk to youlater.” Using the “help;” command will cause the Emic module to output a list of commands that you can view if youhave the Emic module connected to a terminal program. TheEmic module’s documentation is well written and providesdescriptions of the commands not described here.

Wrapping It UpOne thing to keep in mind when using the Emic module

is that speech output does not happen immediately after yousend it something to say. The Emic module needs a briefamount of time to process the text into the necessaryphonemes (the individual sounds that words can be brokendown into). Knowing this, you should try to send it the textto be spoken so that these pauses happen at appropriatetimes, such as the ends of sentences. The reason that you will

need to break up your text is because the Emic module hasa 128-byte buffer to hold commands and text to be spoken. If you wanted the Emic module to say somethinglike, “Four score and seven years ago, our fathers broughtforth upon this continent a new nation, conceived in liberty and dedicated to the proposition that all men arecreated equal,” you might want to send it in the mannershown in Figure 4.

Figure 4 breaks this long sentence into two parts in aplace where there would likely have been a dramaticpause. Neither section of the sentence is longer than 128characters. The “say=” and the semicolon must be countedwhen counting the characters in the buffer. In Figure 4,each sentence fragment is broken into two parts. This wasdone to keep the lines of code short. The Emic module willonly speak once it has received a semicolon.

Adding speech capability to your robot allows it tocommunicate in a very natural way that people can understand. This month, you’ve learned how to easily addthis capability. Now, you can do things like get feedbackfrom your robot projects through the telephone, makeyour robot interact with someone who is blind, or let yourtechnology-challenged friends have fun playing with yourrobots. SV

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10 SERVO 03.2005

www.ccsinfo.comSells the C compiler for PIC processors used in this column

www.microchip.comManufacturer of the PIC microcontroller

www.jameco.com or www.mouser.comPossibly the best sources for electronic parts

www.parallax.comSells the Emic module used in this article

RESOURCES

output_high(RESET); // connected to the Emic’s /RESET pinprintf(“volume=5;”);waitOnBusy();

while(true){printf(“say=Peat and Repeat went into a store;”);waitOnBusy();

printf(“say=Peat came out.;”);waitOnBusy();

printf(“say=Who’s left?;”);waitOnBusy();

delay_ms(1000); // wait one second}

void waitOnBusy(){ // delays until the busy pin goes low

delay_ms(1);while(input(BUSY)){}

}

Figure 3. Code to drive the Emic module.

printf(“say=Four score and seven years ago, our fathers”);printf(“ brought forth upon this continent a new nation;”);// the buffer now has 95 characterswaitOnBusy();

printf(“say=conceived in liberty and dedicated to the”);printf(“ proposition that all men are created equal;”);waitOnBusy();

Figure 4. Code that has the Emic module say a longer statement.


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QWhat is the difference between digital and analogservos? The guys at the local hobby store tell methat digital ones are better because they are

stronger and faster than regular servos, but you can buy different servos that are faster and stronger. The one thing Iknow for sure is that they are more expensive than regularservos. Why do I want to use a digital servo instead of theregular, analog servos?

— Graham WilsonIssaquah, WA

AFor the most part, they are the same. For example, ina given servo class that has both analog and digital versions of the same servos (i.e., the Hitec HS-645

and the HS-5645 servos), they use the same cases, gear sets, bearings, electric motors, and position feedback potentiometer. The main differences between them are theinternal control electronics and the frequency in which theyupdate the motor position.

Before jumping into what is different about digital servos, here is a little background on how analog servos

work, so that you can understand why digital servos are different. First off, analog servos use an analog circuitry tocontrol servo arm position. This usually consists of using resistors, capacitors, transistors, and a custom IC (or two) tocompare the input commanded position to the actual servoposition, which is then used to control the direction of theelectric motor to react to any positional errors.

The first thing the servo’s control electronics does is toreceive the typical one to two ms position command. Then itmeasures the servo arm’s position by reading the voltageacross the potentiometer that is connected to the servo’s output shaft, which is then compared to the commandedposition. If there is any positional error, then a voltage pulseis sent to the motor to force the motor to move in the opposite direction of the measured angular error. This is typical in any servo control application.

What becomes interesting here is how the analog servosgo about implementing this. Here, the control electronics willoutput a simple voltage pulse to the electric motor that isproportional to the positional error. When there is no error,no voltage is being sent to the drive motor, so the servo stopsmoving. When the error is small, the pulse width is small (i.e.,the amount of time the voltage is being applied to the motoris small). As the positional error increases, the pulse widthbecomes longer.

The electric motor will only move a small amount,based on how long the voltage pulse width is sent to themotor. If the pulse width is too small, the servo won’t turnbecause the pulse would not be sufficient for the electricmotor to overcome all of the internal friction inside theoverall servo. As the pulse width increases, the electricmotor will move more. Due to the gear reduction in theservo, however, large electric motor rotations are neededto cause small servo output shaft movements and, therefore, small changes in the servo position’s feedbackpotentiometer.

One of the reasons why the pulse widths sent to theelectric motor are proportional to the positional error is sothat the servo won’t overshoot the desired position. As the

Tap into the sum of all human knowledge and get your questions answered here! Fromsoftware algorithms to material selection, Mr. Roboto strives to meet you where youare — and what more would you expect from a complex service droid?

byPete Miles

Our resident expert on all things robotic is merely an Email away.

[email protected]

12 SERVO 03.2005

Figure 1. An Atmel microcontroller is used to control theHitec HS-5645 digital servo.

MrRoboto.qxd 1/28/2005 4:45 PM Page 12

servo’s output shaft approaches thedesired position, it slows down to minimize any overshooting, which isone of the causes of “servo jitter.”

The reason for the focus on whatthe servo does after it receives oneposition command is that the analogservo’s control electronics will outputonly one pulse to the electric motor for every one to two ms position command it receives. This is why theservo’s commanded position is updated50 times a second (50 Hz) to make surethat the servo completes the move toits commanded position.

Since the commanded position issent to a servo 50 times per second,this, in turn, results in an electricalpulse width being sent to the electricmotor 50 times per second. This, ineffect, creates a PWM (Pulse WidthModulation) signal that controls themotor speed. When the positionalerror is small, the resulting PWM dutycycle is small; therefore, the motormoves slower because the average volt-age is small. As the positional errorincreases, the PWM duty cycle increas-es; the motor’s speed will increasebecause of the higher average voltage.This, then, affects the torque themotor can deliver. Small positionalerrors result in slower shaft speeds,which then result in lower torque.Higher positional errors result in highershaft speeds, which then result in higher motor torque. This is why theservos resist more the harder you try toturn them. The greater the error, thegreater the torque.

When the error becomes largeenough, the resulting pulse width thatis being sent to the electric motor willequal the time period for the incomingcommanded position update frequen-cy. When this occurs, a constant volt-age is sent to the motor and the motordelivers its maximum torque.

One bit of information that fewpeople are aware of is that the incoming position command updatefrequency does not have to be updatedat 50 Hz for a servo to work. The signalcan be either faster or slower. The actualpulse width that is sent to the motor isonly a function of the positional error.The motor speed and torque thenbecome functions of the incoming

position update frequency. Faster frequencies will result in the motorresponding to the errors faster andwith higher torque. Slower update frequencies will result in the motor taking longer to correct positionalerrors and a lower servo outputtorque. If the frequency becomes tooslow, then the servo will start to havenoticeable power losses and will look like it is stepping (pulsing) towardits commanded position instead ofmoving smoothly.

Digital servos work a little differ-ently than this. They still take the sameone to two ms input command pulse,but instead of outputting a single pulse to the electric motor, the microcontroller outputs a continuousPWM signal to a set of transistors/FETsto drive the motor. Figure 1 shows theAtmel microcontroller that is used tocontrol the Hitec HS-5645 digital servo.The PWM frequency for most servos is300 Hz, which is about six to 10 timesfaster than the normal updating signalapproach used with analog servos. Inparallel with controlling the motor position and speed, the microcontrollerin also measuring the actual position ofthe servo and comparing it to the commanded position.

Like with the analog servo, thepulse width of the PWM signal is proportional to the servo position error.When the positional error is zero, thepulse width is also zero, hence a zeropercent duty cycle. As the error increases, the pulse width and dutycycle percentage increases until theerror becomes large enough that aconstant voltage is sent to the motor(100 percent duty cycle).

Hence, the main differencebetween an analog servo and a digitalservo is the PWM frequency for motorposition and speed control. For analogservos, the PWM frequency is driven bythe input position update frequencyand, for digital servos, the PWM frequency is constant (i.e., 300 Hz) andindependent of the input position com-mand frequency. Figure 2 illustrates thecontrol signal differences between ananalog and digital servo.

So, what are the advantages of adigital servo over an analog servo?They boil down to torque and a tighter

13Circle #55 on the Reader Service Card.


dead band. Maximum torque will be the same between thetwo. This is because, once a 100 percent duty cycle has beenachieved, 100 percent voltage (minus any voltage dropacross the transistors) is applied to the motor. Still, the torqueadvantage occurs during small positional errors. For a givenduty cycle, the higher PWM frequency allows more current tocirculate through the motor to keep it turning during the offtimes, which results in the motor turning faster and morepower going through the motor. This results in the servodelivering more torque quicker with smaller positional errorswhen compared to analog servos.

With very small positional errors, an analog servo will

send a single, short pulse to the motor to make it move. Themotor needs a certain amount of electrical current in orderto overcome all of the internal friction of the motor to start moving. When the pulse width is not large enough togenerate enough current to do this, the motor doesn’t move.Because of this, the servo shaft can move a small amountmore or less than its commanded position without being corrected. This small oscillation is known as the dead band.With digital servos, the higher frequency results in more current going through the motor with small positional errors.Because of this, digital servos will start moving with smallerpositional errors than analog servos. Hence, digital servos

have a tighter (smaller) deadband.

For the R/C car and aircrafthobbies, the digital servosmean faster response, moreholding/transient torque, andtighter dead band control. Thismakes them very popular forthe high-performance people.For the robotics community,though, are these advantagesreally that important?

Hopefully by now you havenoticed that the only differencebetween analog and digital ser-vos is that the PWM frequencyto the electric motors and thedigital servo frequency is fixedat 300 Hz. The analog servo frequency, however, can bechanged to whatever you want.The R/C community is stuckusing their transmitters andreceivers that only update theservo’s position at a frequencyfrom 30 to 50 Hz. With robotmicrocontrollers, though, theservo motor’s PWM frequencycan be easily increased just byincreasing the input positionfrequency. In fact, just bychanging the frequency of theone to two ms input positionupdates, you can control theservo speed. Thus, the lowercost analog servos can be madeto perform as good as or betterthan the more expensive digitalservos.

This is not to say that digi-tal servos don’t have their placein the robotics community.Some servo manufacturers haveservos that are programmable,and these programmable features can be very beneficial

14 SERVO 03.2005

20ms 40ms

20ms 40ms

20ms 40ms

20ms 40ms

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20ms0 40ms

20ms

20ms

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40ms

INCOMING POSITIONCOMMAND PULSE

NO POSITIONERROR

NO MOTOR PWM

SMALL POSITIONERROR

LOW MOTOR PWMDUTY CYCLE

MODERATE POSITIONERROR

MOTOR PWM DUTYCYCLE AROUND 50%

LARGE POSITIONERROR

HIGH MOTOR PWMDUTY CYCLE

ANALOG SERVO DIGITAL SERVO

4

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Figure 2. Illustration of the control signal differences in an analog and digital servo.


to robots. Right now, there are only twoprogrammable servo manufacturers onthe market — Ko Propo and Hitec.Multiplex has a programmable servoline, but they only allow you to reversethe servo direction.

The speed, dead band, and servotravel of the digital servos sold by Ko Propo (www.kopropo.com) are programmable with a PC. The servoscan be programmed to move faster orslower, increase or decrease the deadband, and create soft limits on therange of motion the servo can travel. Inaddition, you can program both the rateof speed change at the dead bands(called punch) and the overshootallowance at the servos.

An interesting feature is that anover-current protection can be pro-grammed into the servos. If a maximumamount of current is detected for a certain amount of time, the servos willautomatically reduce power. This can bevery beneficial in preserving theseexpensive servos. Ko Propo also has aclass of three servos called the “RedVersion” (KHR-8044 ICS, KHR-2346 ICS,KHR-949 ICS). These digital servos arenot only programmable, but they canprovide an actual position feedback. Thisis beneficial for developing advanced animatronic posing programs or closedloop servo position algorithms. The KoPropo servos are very popular in Japanand Korea for many of the humanoidrobots that compete in the Robo-Oneevent (www.robo-one.com). The onlysource for them that I am aware of in the US is HorizonHobbies (www.horizonhobbies.com).

The digital servos from Hitec (www.hitecrcd.com)require a separate hand-held programmer called the HFP-10Hitec Digital Servo Programmer. With this programmer, youcan set the dead band width, servo rotation direction, servospeed, enable/disable failsafe, and the range of motion andneutral position. Failsafe is a position where the servo will move to if it stops receiving a position command, which is very important for model aircraft. The hand-held programmer has its own batteries so the servos can be programmed in the field. Also, the programmer can be usedto test the servo to see if it is working properly.

For robotics applications, the Hitec digital servos havea very nice feature that — to my surprise — no one has ever figured out or published. These servos do not require theposition command to be repeated as long as the failsafehas been disabled (which is the default). When you firstapply power to the servo, it won’t move for about a second. Then, wherever its current position is, it will hold

that position. All you have to do is send the one to two msposition pulse to it once and it will move to that positionand stay there until told to move differently. This is a greatadvantage for robotics because it eliminates all of the

SERVO 03.2005 15

Specification AI Motor-601 AI Motor-701 AI Motor-1001

Input Voltage Range 5 to 10 volts

Max. Torque @ 9.5 V 83 oz-in 97 oz-in 139 oz-in

Max Speed @ 9.5 V 90 RPM 82 RPM 60 RPM

Gear Ratio 1/160 1/173 1/241

Gear Material Plastic Plastic Plastic & Metal

Bearings None None Yes

Size 51.6 x 34.3 x 37.1

Weight 40 grams 40 grams 46 grams

Mechanical Connection Points Two

Electrical Connection Points Two

Control Signal RS-232

Baud Rate 2400 to 460800 bps

Number of Modules Per SerialLine 31

Angular Controllable Range 0 to 332 degrees

Angular Resolution Two levels, 1.3 degrees, 0.65 degrees

Inverse Voltage Protection Yes

Over-Current Protection Yes

360 Degree Rotation Function Yes

Position Feedback Function Yes

Current Feedback Function Yes

Speed Control During PositionControl Mode Five levels

Speed Control During 360 DegreeRotation Mode 16 levels

Table 1. Megarobotics Actuator Module (servo) specifications.

Figure 3. Megarobotics AI Motor-601 Modules.


position update overhead headaches that are associatedwith analog servos. This feature alone makes Hitec digitalservos my servo of choice.

QI want to build a model of one of those industrialrobots that are used to weld automobiles. Are thereany hobbyist level servos that have a greater range

of angular motion than the standard R/C servos?— Mark Packs

Indianapolis, IN

ATake a look at the Megarobotics AI Modules that aresold by Tribotix (www.tribotix.com). These servos areabsolutely amazing. Since typical servos have a

maximum angular range of motion of 180 degrees and these

servos have a range of motion that is 332 degrees, I thinkthey will work quite well for your application. Table 1 showsa list of the specifications for these motors. Figure 3 shows apair of the AI Motor-601 Modules.

These servo modules have similar size, torque, and speedratings as the higher-end R/C servos, but their many otherfeatures make them ideal for the robotics community. Forexample, many people will permanently modify R/C servosby gutting them so that they can rotate 360 degrees. The AIservos can operate in either position control or continuousrotation mode by a single program command. In addition,variable speed is also programmable, which eliminates theneed for a separate speed controller. Since these servos provide both position and current draw feedback, closedloop position control systems can be created with over-current protection that will prevent the motors from becoming damaged.

These servos are programmed using standard RS-232 signals and the control signals do not need to be repeatedfor the servos to hold their position. With baud rates up to460 kbps, multiple servos can be simultaneously controlledwithout any noticeable lag between the first and last servoposition command. Another attractive feature of these servos is that they can be daisy chained together so that asingle serial control line can control up to 31 different servos. The daisy chaining greatly simplifies the wiringbetween the servos and a microcontroller.

Typical R/C servos come with four different servo hornsthat can only be attached to the output spline of the shaft.The AI Motors come with 11 different attachments that connect to the output shaft and to the motor’s frame. Theseattachments allow multiple motors to be connected to eachother without having to use additional mounting brackets.One of the other features that make these motors unique isthat there are two different attachment points on the

output shaft. One is on the side of themotor, which is similar to regular servos and the other is at the midpointof the body. This allows motors to bemounted inline with each other andreduces the bending stresses on theoutput shaft. Figure 4 shows the vari-ous attachments and replacementgears that are included with every AImodule.

These motors are relatively new tothe robotics community, but they arebecoming more and more popular.Due to their modularity and ease ofprogramming, they are becoming fairlypopular in the humanoid andquadruped robotics communities.

Though Tribotix is located inAustralia, it took less than a week forthe servos that I purchased to reachSeattle. I was quite amazed, since itusually takes a month to get parts fromJapan. SV

Figure 4. Various attachments and replacement gears that areincluded with each AI Motor Module.

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16 SERVO 03.2005


HobbyEngineeringHobbyEngineeringHobbyEngineeringHobbyEngineeringThe technology builder's source for kits, components, supplies, tools, books and education.

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Motors, Frame Componentsand Scratch Builder Supplies.

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SERVO 03.2005 17

Full Page.qxd 2/2/2005 4:13 PM Page 17

18 SERVO 03.2005

There are a few interesting events shaping up forMarch, including the annual APEC Micromouse competition,which will be held in Austin, TX. Also planned for March isthe second ROBOlympics, which promises to be even biggerthan last year’s event, with over 50 events scattered acrossthe San Francisco State University campus.

The list of events for April and May — which tend tobe the busiest months — continues to grow as we getfinal event information from organizers. We’re listingsome new events this year, including TEAMS, which is aFIRST-like organization for Maryland middle schools. Alsonew to the list is Istrobot — a university-level event held inSlovakia.

— R. Steven Rainwater

For last minute updates and changes, you can always findthe most recent version of the complete Robot CompetitionFAQ at Robots.net: http://robots.net/rcfaq.html

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6-10 APEC Micromouse ContestHilton Hotel, Austin, TXThis will be the 18th annual APEC Micromouse event.www.apec-conf.org/

11-12 AMD Jerry Sanders Creative Design ContestUniversity of Illinois at Urbana-Champaign, ILThe design problem for this contest is new and different each year. Check the website for the latestnews and details.http://dc.cen.uiuc.edu/

19-20 Manitoba Robot GamesManitoba Museum of Man and Nature,Winnipeg, Manitoba, CanadaA variety of events, including sumo, a robot tractorpull, and Atomic Hockey.www.scmb.mb.ca/

24-27 ROBOlympicsSan Francisco State University, San Francisco, CALots of events, including sumo, BEAM, Mindstorms,

FIRA, and robot combat.www.robolympics.net

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9-10 Trinity College Fire Fighting Home Robot ContestTrinity College, Hartford, CTCould the fire have been set by a robot builder frustrated with the voluminous rules?www.trincoll.edu/events/robot

12-14 DTU RoboCupTechnical University of Denmark, Copenhagen, DenmarkImagine your typical line following contest. Nowadd forks in the line, ramps, stairs, gaps in the line,shifts from indoor to outdoor lighting, reversals ofthe line shading (white to black), and 50-cm“gates” though which the robot must pass.www.iau.dtu.dk/robocup/about_robocup.html

15 Carnegie-Mellon Mobot RacesWean Hall, CMU, Pittsburgh, PAThe traditional Mobot slalom and MoboJoustevents will be hosted by CMU.www.cs.cmu.edu/~mobot/

16 UC Davis Picnic Day Micromouse ContestUniversity of California at Davis, CAEvery year, UC-Davis has a campus-wide eventknown as Picnic Day. Every Picnic Day includes theannual micromouse contest. The event followsstandard micromouse rules.www.ece.ucdavis.edu/umouse/

21-23 FIRST Robotics Competition (National Championship)Georgia Dome, Atlanta, GACorporate sponsored teams of students from allover the country will converge on the GeorgiaDome to pit robots designed from standardized kitsof parts against each other. See the website fordetails on this year’s competition.www.usfirst.org/

Send updates, new listings, corrections, complaints, and suggestions to: [email protected] or FAX 972-404-0269

Events.qxd 2/3/2005 11:19 AM Page 18

23 RoboFestLawrence Technological University, Southfield, MIA competition and exhibitionof autonomous LEGO robotsdesigned to spur students’interests in science, engineering,programming, and technology.http://robofest.net/

27 IstrobotSlovak University of Technology, SlovakiaThis competition is held bythe Robot Group within theDepartment of Automationand Control at the university.Events include line following,mini sumo, standard IEEEMicromouse, and a free styleevent where you can showoff anything your robot does.www.robotics.sk

28-30 SAE Walking Machine ChallengeMontreal, Quebec, CanadaThis is the best place to seeinnovative and unusual walk-ing robots every year.www.sae.org/STUDENTS/walking.htm

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10-11 RoboBusiness Conference Hyatt Regency, Cambridge,MAThe nation’s premier businessdevelopment event for mobilerobotics and intelligent systems, dedicated to the commercialization and applica-tion of robotic systems.www.roboevent.com

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SERVO 03.2005 19

RRoobboottiiccss SShhoowwccaasseeRRoobboottiiccss SShhoowwccaassee

Events.qxd 2/3/2005 11:44 AM Page 19

SUPPLIER

Model N

umber

Description

Width (in)

Length (in)

Height (in)

Weight (oz)

Speed: sec/60° (4.8 volts)


Torque: oz-in (4.8 volts)


Servos

20 SERVO 03.2005

Airtronicswww.airtronics.net

94359ZERG-VX High Torque

Aluminum Heatsink Servo1.54 0.79 1.47 2.19 0.13 0.10 N/A 160

94758ZCompetition Digital Servo

High Torque1.54 0.79 1.47 2.12 0.07 0.06 N/A 92

Cirruswww.globalhobby.com/cirrus/cirrus.htm CS-80MG Pro 1.60 1.49 0.79 2.01 N/A 0.25 N/A N/A

Futaba Digitalwww.futaba-rc.com

S3305Standard H/D With

Metal Gear1.60 0.80 1.50 1.64 0.25 0.20 N/A 99

S9206Heli/Air High Torque

Metal Gear1.60 0.80 1.50 1.90 0.19 N/A N/A 132

S9350High Torque Steering

Metal Gear1.60 0.80 1.50 2.10 N/R 0.12 N/A N/R

S9351 High Torque 1.60 0.80 1.40 2.10 N/A 0.15 N/A N/A

Hitecwww.hitecrcd.com

HS-645MG High Torque Metal Gear 1.55 0.78 1.48 1.94 0.24 0.20 N/A 107

HS-945MG High Torque 1.55 0.78 1.48 1.97 0.16 0.12 N/A 122

HS-5945MG Digital High Torque 1.55 0.78 1.48 1.97 0.16 0.13 N/A 153

HS-5995TG Digital X-Servo 1.57 0.78 1.45 2.18 N/A 0.15 0.12 N/A

JR Servoswww.jrpropo.co.jp/e_index.html DS8611 Digital High Torque 1.58 0.82 1.56 2.24 0.18 N/A N/A 220

Kondowww.kondo-robot.com/

KRS-784ICS KHR-1 Robot Servo 1.61 0.82 1.37 1.58 N/A 0.17 N/A N/A

KRS-2346ICS Red Version 1.61 0.79 1.49 2.00 N/A 0.16 N/A N/A

KO PROPOwww.kopropo.com/home.htm

PS-2174 FET PS-2174 FET 1.61 0.79 1.50 1.92 N/A 0.13 N/A N/A

PDS-2144 FET PDS-2144 FET 1.61 0.79 1.50 1.93 N/A 0.13 N/A N/A

BrainMatrix.qxd 2/3/2005 10:30 AM Page 20

Additional Options

Price

Digital Analog

Motor

Gears: M

etal/Plastic

Torque: oz-in (6.0 volts)

Torque: oz-in (7.2 volts)O

utput Type

SERVO 03.2005 21

So, you want to build a Robo-One biped robot, but don't know which servos to use. There are so manyoptions and models to choose from. Do you use analog or digital? How much torque do you need? Whatabout price? I have created this issue’s “Brain Matrix” comparing most of the major brands and standardsize models of servos that might be useful in a Robo-One.

Guest Hosted byPeter Abrahamson

260 N/A Dual Coreless P/M D $114.99 N/A

119.6 N/A Bushing Coreless P D $65.00 Rear Bearing Hub/ICS

275 N/A Dual BB Coreless M D $175.00 Rear Bearing Hub/ICS

131.9 N/A Dual BB Coreless M A $109.99 N/A

166.6 N/A Dual BB Coreless M A $109.99 N/A

200 N/A Dual BB Coreless M A $104.99 N/A

115 N/A Dual BB Coreless M D $99.99 N/A

130 N/A Dual BB N/A P/M A N/A N/A

125 N/A Bushing N/A M A $37.99 N/A

N/A N/A Dual BB Coreless M A $89.99 N/A



133 N/A Dual BB Three Pole M A $39.99 N/A

153 N/A Dual BB Coreless M A $73.99 N/A


330 412 Dual BB Coreless M D $114.99 Rear Bearing Hub

One of the first questions asked whensomeone is building a Robo-One is “Do I useanalog or digital servos?”There are some amaz-ing analog servos out there. In my days of build-ing animatronics, puppets, and robots for thefilm and TV industry, we used the Airtronics94358 and 94359 servos for many applica-tions. The torque for the package size wasamazing — 200 oz-in! The price for an analogservo was usually less than that of a digital one,but that seems to be changing.

Now, with digital servos, a whole array ofoptions open up for you.With the Hitec digitalservos, you can buy a servo programmer (theHitec HFP-10) that allows you to set limits,reversals, offsets, and speeds within the servo,rather than wasting valuable memory in therobot’s brain. The new digital servos have higher torque and speed ratings than most analog servos.

Some servos are specifically designed forrobots. Hitec has the HS-5995TG with 330 oz-in of torque, titanium gears, and a spur on thebottom of the servo for mounting a bearing.Kondo — the manufacturer of the KHR-1 robotkit — has come out with a couple of robot-specific servos: the KRS-784ICS and KRS-2346ICS Red Version. For around $65.00, theformer is used in the KHR-1 kit and comes withplastic gears, 119 oz-in of torque, and a bear-ing spur. The Red Version has 275 oz-in oftorque, metal gears, an option for a bearingspur, and mounting tabs on the rear of theservo; when used with the RCB-1 (Kondo’s robotbrain), it can give position feedback. Kondo servos use ICS (Interactive CommunicationSystem) for feedback and control.

Left to right:Airtronics 94359, KondoKRS-2346ICS Red Version, Hitec

HS-5995TG, and the Kondo KRS-784ICSin the feet of the KHR-1 robot.

BrainMatrix.qxd 2/3/2005 1:48 PM Page 21

WWhen we first learned that the next tweak would involve an R/Cboat, the natural choice for a

modification was to make the vehicleamphibious — capable of traversingboth land and sea, but we were surprised to find that our next projectwas the Land Sea 2 R/C, an alreadyamphibious vehicle! We decided totake the all terrain idea to the next leveland make the vehicle capable of flight,as well. Jet engines would be tricky toadd to an R/C car, so we thought a helicopter-like rotor assembly would bethe best thing to help the Omni-TerrainVehicle take to the skies.

The Land Sea 2 R/CThe Land Sea 2 R/C is definitely an

impressive unit. It sports three modes of operation — land, sea, and tank(another option for land travel). Theland version is definitely zippy and it’seven capable of carrying two full sodacans (a strange ability, but coolnonetheless). The steering for the seamode is difficult to get used to, but funonce you master it. The tank mode is aninteresting option, but, as the instruc-tion manual warns, it is difficult to getthe wheels to make the 1/3 of the fullrotation for optimum maneuverability.

Other added bonuses includephotosensitive headlights (with anoption to have them turn on onlywhen it’s dark) and a function thatmakes the vehicle turn on its pro-pellers to run in circles when it is outof the range of the controller. Thecontroller itself is also water-resistant.The vehicle is certainly multifunctionaland it actually performs all of thosefunctions well.

Now, despite the warning on theinstructions that read: “Modificationsnot authorized by the manufacturermay void user’s authority to operatethis device,” we proceeded to make the Land Sea 2 R/C even more multifunctional.

Problem AnalysisCreating a vehicle that can move on

land, in air, and on water is definitely acomplex problem. At least for us, landand sea movement has been takencare of, but adding the ability to fly isstill tricky. The main additions that weneeded to concentrate on were givingthe vehicle enough lift to fly, whilekeeping it afloat with the addedweight of the rotor assembly. Luckilyfor us, physics comes to the rescue.

22 SERVO 03.2005

The Omni-Terrain Vehicle

Tweaking theLand Sea 2 R/C

Before and After: A grounded Land Sea 2 R/C is made to fly.

TwinTweaks.qxd 1/28/2005 4:35 PM Page 22


Ultimate PastaOur primary concern is getting the

vehicle off of the ground. We wereawash in ideas for propeller systems,but Bernoulli’s Principle helped uswring out implausible ideas. Bernoulli’sPrinciple, for our purposes, explains the phenomenon of lift that allows airplanes to fly. Bernoulli’s equationelucidates this principle mathematically:

∆P=1/2 ρv top² - 1/2 ρv bottom²

This equation helps you figure out∆P — the change in pressure betweenthe top of the wing and the bottom — byusing the differences in the velocity ofthe airflow over those surfaces. The dif-ference in the velocities above and belowthe wing results from the shape of thewing that deflects air molecules on thebottom, slowing them down and creat-ing lift. Lift is easy enough to create, butcreating enough of it is the problem.

Something will lift off the groundif the force of lift is greater than theforce of gravity acting upon whatever itis that you want to make fly. Force ofgravity is easy to figure:

Fg=mg

m being mass and g acceleration dueto gravity, 9.8 m/s².

The mass of the Land Sea 2 R/C is1.07 kg, so the force of gravity is 10 N.Allowing for some extra weight for therotor assembly, we can estimate thatthe force of lift necessary for flightmust be greater than 20 N. Liftingforce can be determined by Bernoulli’sequation, which helps determine ∆P.The equation for pressure can bemanipulated to determine force.

P=F/A , F=PA

Lifting force can be determined bymultiplying the difference in pressurecreated by the shape of the wings by thearea of the wings. Thus, we can see thattwo variables determine lifting force: thedifference of airspeed over and underthe wings and the area of the wings.The solution seems simple, at first: Slapon a fast motor with a giant rotor.

Several design considerations,however, need to be taken intoaccount and the obvious one is weight.If the motor and rotor are too heavy,too much buoyancy would need to beadded and things would get ridiculous.Another consideration lies in the characteristics of the motor. We want afairly light motor to avoid buoyancyproblems.

Like we stated before, the keyabout Bernoulli’s Principle is that thedifferences between velocities of air onthe top and bottom of the wing createlift, and that difference is created bythe classic airfoil shape of the wing.Instead of giving the Land Sea 2 R/C jetengines and wings, we decided that ahelicopter-like rotor would be the wayto go. Rotors use the same principle,while lift is achieved by the bend in therotor instead of an airfoil shape. Moreof a bend creates more of a differencein airspeed and, thus, more lift. Whatwe have to be careful about is thatmore of a bend creates more air resistance, and we don’t want to create too much of a bend so that itcreates too much resistance and over-comes the torque of the motor.

Rotors, Archimedes,and Buoyancy — Oh My!

Buoyancy is the other side of this problem. To keep things simple, itwould be best to create a rotor assemblylight enough so that the vehicle wouldstay afloat without extra modifications.Calculating the buoyant force on theoriginal, untweaked vehicle wouldgive us a ballpark range of what kindof weight we could use for the rotorassembly. As long as the combinedweight of the vehicle and rotorassembly doesn’t overcome the buoy-ant force possible for the originalboat, the tweaked vehicle will stayafloat.

The phenomenon of buoyantforce is known as Archimedes’Principle and can be calculated withthe following equation:

B=ρf Vg

B is buoyant force in Newtons, ρf is thedensity of the fluid (in this case, water),V is the volume of displaced water, andg is acceleration due to gravity.According to Archimedes’ Principle,buoyant force is created by the displacement of water. Buoyant forceon a floating object is equal to itsweight in air, so adding weight requiresadditional buoyancy.

The rotor assembly wouldn’t displace any water, so the additionalbuoyant force would have to comefrom the vehicle riding lower in thewater. This wouldn’t be a problem if theoriginal vehicle floated high enoughand gave us some room for extraweight, but after testing it in water,though, we found that it floated sur-prisingly low without any extra weight.

The two solutions would be tolighten the boat or add buoyancy. TheLand Sea 2 R/C is a very clean unit andhacking into something meant to floatis a leaky proposition, so we decidedextra buoyancy would be the way togo. TV bodgers on Junkyard Wars and

SERVO 03.2005 23

For rotors, the bend causes lift instead of an airfoil shape

used on wings.

We’ll use the tiny Fisher-Pricemotor found in Power

Wheels products.


Monster Garage usually use drums or barrels to increase buoyancy onfloating projects, but — since an oildrum is a little oversized for our vehicle— we decided to use Styrofoam.

Design ConsiderationsGalore

That’s a lot of physics, so let’s stopand review our objectives. Our primaryconcern is making the vehicle fly. We’vesettled on a helicopter-style rotor bladefor lift, powered by a tiny but powerfulFisher-Price motor (the kind they use inPower Wheels, but without the gearbox). The two variables that deter-mine lift are the area of the rotor andthe difference in air speed above andbelow the rotor. Ideally, we need a fastrotor with a healthy bend in it and lotsof surface area.

Our second consideration is maintaining the ability of the vehicle to

traverse land and sea. Land is noproblem, but — to keep the boat afloat — we will addStyrofoam to increase buoyancy,compensating for the weight ofthe rotor assembly.

Knowing the physics is onething, though, and having theinstrumentation to implement thephysics accurately is another. Wedon’t have the means to make theultra-precise measurements thataccurate implementation of theformulas calls for, but the simpleknowledge of the principles will

guide us to make tolerably educatedestimations of what we need to do tomake this ambitious project successful.

Construction and First Tests

The first assembly we did was thatof the rotor. For the blade itself, wechose a piece of 0.095-inch-thick aluminum, which was the thinnestpiece of aluminum we had that waslong enough for a rotor. We cut a piece12 inches long and 1-3/4 inches wide,which we felt gave a fair amount ofsurface area without being too heavy.

The output shaft of the Fisher-Pricemotor had a gear attached to it, so wedrilled out a slightly smaller hole andfiled in some grooves for the teeth tofasten to the rotor for a snug fit. Aftermanaging to get the rotor to fit, wemoved on to bending it. Helicopterrotors do not have the classic wing

shape of an airfoil; their rotors aresimply flat, but bent diagonally. Tobend it nicely, we used scrap aluminum channel to make a largelever and stuck it in a large vice.

Once we had an acceptablebend, we could attach the rotor tothe motor, but we had to be carefulto fasten the motor with the right ori-entation. To create lift, the high edgeof the rotor needs to be the leadingedge. If we got it wrong, we’d havea Land Sea 2 R/C with a large fanhacked onto it. Once we checked therotation of the motor, we attachedthe rotor accordingly, and to makesure we had a solid attachment, wewanted to use some epoxy. All we

had lying around the garage, however,was some J-B Stick Weld used for mend-ing leaky pipes. Oh well, when hackingsomething, you use what you can.

We could have used Bernoulli’sequation to figure out exactly howmuch surface area we needed from therotor and the bend we needed in it,but using the means at our disposal,that would be a difficult task. Instead,we relied on educated estimations (theSWAG theory).

Twenty-four hours later, after theepoxy had fully cured, we set out towire in a switch. Our plan was topower the motor off of the six-volt bat-tery pack that the R/C car used. To giveus some control over the rotor withouthaving to hack into the electronics ofthe waterproof R/C, we wired in ourown switch. Our initial idea was to fas-ten the switch to the vehicle itself, butwe realized that might entail reachingour hands under a spinning rotor toturn it off, so we thought a moreremote switch would be prudent.

Here, we came to one of the mostfrustrating parts of the tweak. The bat-tery pack slid in sideways beneath thecockpit of the vehicle and it was a verytight fit. Luckily for us, the battery packhad four contact points and the LandSea 2 R/C only used two. We used theother two for the motor connections.The problem was that the connectionswould work when the battery was out-side of the vehicle and not when it wasinside. We tried over and over, butnothing worked. We even consideredsoldering the wires to the contactpads, but the pads were dirty and wewere out of acetone.

A solution finally presented itself inthe form of aluminum foil. We twistedlittle bulbs of aluminum foil onto theends to increase the surface areathrough which electricity could travel.After this simple step, the circuit had noproblems whatsoever. Once the switchcircuit was completed, we wanted totest the rotor. In order to minimize danger, we only flipped the switch for asecond, but — even then —we couldsee that the rotor would spin frighten-ingly fast. This test was both promisingand unnerving, because we saw thattesting it could be very dangerous.

24 SERVO 03.2005

Twin TTweaks ....

For the blade, we chose a piece of0.095-inch-thick aluminum, 12 inches long.

To create lift, the high edge of therotor needs to be the leading edge.


Our next task was to actually makethe rotor assembly and Land Sea 2 R/Cinto one piece. For the sake of balance,we wanted to attach the rotor assem-bly in the center of the vehicle. Oneproblem was that the cockpit was inthe middle of the vehicle. We decidedthat we really didn’t need the cockpitand removed it, but the one potentialissue that came with the cockpitremoval was that we were simultane-ously removing the R/C’s antenna.

We tested the range of the vehicleminus the antenna and found it to be atolerable six feet. Cockpit removal alsogranted easy access to the batterypack. We fashioned a platform out ofcardboard to support the motor andattach it to the vehicle, and everythingwas bound together by generousamounts of duct tape. We figured thatenough duct tape would maintain theintegrity of the vehicles’ waterproofreputation and the addition of ducttape made the project a true hack.

Even though the manner of attach-ment may sound rudimentary, therotor assembly was surprisingly stable.Now that the vehicle was assembled,we were ready for the first test.

Keeping safety in mind, we broughta blanket out during the test in case theOmni-Terrain Vehicle went crazy. Wereally didn’t have a terribly good meansof controlling the vehicle’s flight, exceptthat we might use the propellers for thesea mode as stabilizers.

From behind the safety of a trashcan, we hit the switch. The rotor spun upto a frightening speed, causing the vehi-cle to shudder like a fish out of water.Much to our relief, the rotor seemedfirmly attached to the motor and it did-n’t appear to have the desire to fly off.The vehicle itself, however, did not fly.

Back to PhysicsTo better our chances of getting

off the ground, we can look at the twovariables we can easily manipulate.One is the difference in the airspeedabove and below the rotor. To makethat difference greater (and thereforethe lift greater), we would have toincrease the angle of the bend. Withthe rotor assembled, that would be

unduly difficult. Our other optionwould be to increase the surfacearea of the rotor. All we wouldhave to do is add extensions ontothe rotor. While that would be difficult with the assembled piece,it was still our best option.

Two 0.06-inch-thick aluminumplates were perfect for the job,and we riveted them onto the rotorwith little difficulty. Now, ourOmni-Terrain Vehicle had rivets,just like a real airplane. This wasalso an opportunity to test the seaworthiness of the vehicle, butto our dismay, the Omni-Terrain vehicleseemed to have lost its sea legs.

That, however, was an easy problem to solve. All we had to do wasdisplace more water to increase buoyantforce, and duct taping Styrofoam to theboat hull was an easy solution to thisproblem. Soon, the boat was once againable to float. After charging the battery,we were ready for our final test.

All the Omni-Terrain Vehicle need-ed to do for a “Done” stamp was to fly.We hit the switch. The rotor spun up.The vehicle shuddered and even beganto hover slowly across the surface ofthe driveway ... but it still did not fly.

Final ThoughtsThe Omni-Terrain Vehicle was still a

success, despite the fact that it did notgive a satisfactory demonstration of fly-ing ability. The idea of making a vehiclecapable of land, sea, and air movementis certainly a daunting task under anycircumstances — even more so under atime limit. Now that we think aboutit, perhaps the more ideal situationwould have been to make an airplane capable of land and seamovement.

Also, we may have overestimatedthe stamina of the Fisher-Pricemotor (Power Wheels aren’t meantto fly) and of the battery pack. Thebattery pack was actually a six-voltpack we happened to have fromanother R/C car and it was far pastits prime. Oh well. Sometimes, themachines on Monster Garage don’twork as expected, either.

What we turned out to have

made was more like a hovercraft thanan airplane, but we were able to leaveland and sea movement uncompro-mised. The hovering is actually quiteeffective on low friction surfaces, so —if the Omni-Terrain Vehicle ever cameacross a frozen lake — its new hoveringability would likely give it more mobilitythan its regular land mode.Additionally, we gave the Land Sea 2R/C a nasty weapon in case a combatrobotics competition pops up.

In short, the functional shortcom-ings of this project are far from failure;quite the contrary. We learned aboutthe nature of flight through an interac-tive application of physics andresourceful ingenuity.

In fact, the versatility of this drivesystem may even serve as a conceptualprototype for future robotic militaryreconnaissance vehicles (we’ll keep oureyes open for DARPA contracts askingfor Omni-Terrain Vehicles). After all, weare the Woolley Brothers, not theWright brothers. SV

SERVO 03.2005 25


On the first test run, the rotor spunup to a frightening speed!

The Omni-Terrain Vehicle was stilla success, despite the fact that it

didn’t fly.


26 SERVO 03.2005

by Edward Driscoll, Jr.

The dream of a walking mechanical man is almostas old as civilization itself. As I wrote in the debut

issue of SERVO, it’s certainly almost as old as the filmindustry: 1927’s Metropolis, 1956’s Forbidden Planet,1977’s Star Wars, and numerous films since all hadwalking, human-shaped robots as stars.

However, building a real walking robot has beenmore problematic — and controversial. Americanrobot pioneer Dr. Joseph F. Engelberger once toldme, “I don’t want to see a two-legged robot. I feelvery strongly against legs,” because of the complexdesign challenges they present and because of thebetter weight ratios and stability of wheeled robots.Yet, walking robots have seemingly become anobsession in Japan, most famously with Honda’srecent Asimo robot.

Closer to home, in the cold, brutal climate ofAlaska, Carlos Owens — a 27-year-old iron workerand ex-Army heavy equipment mechanic — isbuilding some unique heavy equipment of his own.

Driscoll.qxd 1/28/2005 10:36 AM Page 26

Take Control of an 18-Foot-Tall Walking Robot

The NMX041-AReports forDuty

The Honda Asimo is onlyabout four feet tall. ButOwens is a man who — at sixfeet five inches — not only isbig, but thinks big as well. He noticed that, “All these companies seem to be manu-facturing these robots on avery similar scale.”

So he decided to build awalking robot that’s over three timestheir height “instead of a five-footrobot that looks like all the other five-foot robots.”

So he designed and is well on theway to completing an 18-foot-tall, 8-1/2-foot-wide, 1-1/2-ton, two-legged, two-armed robot that he’sdubbed the NMX041-A. It is designedso that the operator will sit inside of it.

“I actually came up with my own list of standards for mech-typeapplications. The N and M stands for‘neo-mech’ and X is type of chassis —it’s humanoid-thpe. As far as the num-bers, I started it in 2004, hence the‘04,’ the ‘1’ is to designate it as thefirst prototype, and the ‘A’ represents‘arena-type,’ as in a fighting type ofrobot.”

While it’s the first prototype hebuilt in 2004, it’s actually based on anexperiment with an even larger robot:the 25-foot NMX03. “That one wasoriginally going to be 25 feet tall —which is far too large — and justpresents a lot of issues. Everyfoot that you go up, more andmore issues need to be takeninto consideration because of thebalance.”

Fortunately, Owens was ableto reuse some of those parts inthe only slightly more modest 18-foot robot.

Learning to WalkOf course, one of the keys to

building this type of machine is

balancing it while it walks. Like natureitself, four-legged robots are somewhateasier to build because they’re more stable. It may be why industrialdesigner Syd Mead painted an

The operator encased in his machine.

Alaskan conditions make building difficult.


Not having a shop big enough, Carlos builds outside, in the elements.


elephant-like, four-legged walkingmachine that predates the Imperialwalkers from 1980’s The Empire StrikesBack by about 20 years.

In a two-legged machine, though,extra effort is required to balance it inmid-stride. Owens says he hasdesigned “a separate unit which will be attached to the machine upon completion that allows it to shift itsweight from one side to the other

without causing any instabilitieswhile in mid-stride.”

He’s not afraid to admit that hewants to keep its design a secret.“I’ve already been asked severaltimes, but I don’t want to get intothe specifics of that unit, whichallows the whole system to work.

Anyone can build a giant robot, butanyone who wants to make it walk —they’re on their own!”

For much of the year, Alaska is acold and unforgiving environment tobuild in, but Owens is undeterred. Hesays the only concession against thecold he’s needed to make is to heatthe hydraulics used to power theNMX041-A’s joints. “The way I position the hydraulic fluid reservoir

near the engine, where it willheat it up, will also help. Itshouldn’t take too long forthe system to get warm; it should have good fluidmovement.”

The Arena Robot League

He calls the NMX041-A a fighting robot and he envi-sions being the commissionerof an arena league of roboticgladiators — sort of like cable

TV’s Battle Bots or Robot Wars, but ona much, much larger scale.

“The whole idea behind it is thatpeople would be piloting thesemachines and doing battle with oneanother. I’ve got a whole slew of rulesand regulations that I’ve been workingon just for this particular sport that I’min the process of developing.”

As with many inventors, when listening to Owens describe his robotand what he’d like to do with it, it’ssometimes tough to find where realityends and science fiction begins. Whilehe’s building quite an impressive looking machine (which vaguelyrecalls the toy Transformer robots of the 1980s, but on a mammothscale), he’s certainly happy to

pepper his speech with sci-ficatch phrases like “mecha,” and his website has paragraphsthat make his one-man operation sound like the Tyrell Corporation from BladeRunner. For example, Owens’ website is calledwww.neogentronyx.com Saywhat?

Owens says it’s a break-down of a few different words:“‘neo’ meaning new, ‘gen’ isshort for ‘generation,’ and then‘tronyx,’ of course, means electronics. I just spelled it a little differently; I didn’t want todo things the standard way. It’ssomething different — like myproject!”

Perhaps because his projectis so visually exciting, Owens’

28 SERVO 03.2005

INSIDE THE IRON MAN

The only secrets are the stability controls.

A frame supports the robot while under construction.

Carlos Owens, on the shoulders of a giant.

The NMX041-A stands nearly 20 feet tall.


home page is getting much more attention than he originally anticipated. The popular C/Net website profiled him in December. “Ithought that 7,500 hits over a two-year period was pretty good, butI got 40,000 in under just two daysfrom that C/Net article!” He’s hopingit will lead to outside monetary contri-butions to his heretofore self-fundedefforts. (So far, Owens has sunk about$15,000.00 into his project.)

Putting Out a Fire From Inside

Of course, walking robots havemany other applications beyond bashing each other’s hydraulics intothe ground inside a sports arena. Oneapplication that Owens is particularlykeen on is fire fighting. Owens saysthat his robots would provide firefighters, “with a much greater advantage over how we currently

fight fires.” This is particularly truewith forest fires, which involvedropping loads of flame retardantchemicals and water from aircraft.“It pretty much disperses as soonas it hits the air.” In contrast,Owens’ walking robots would walkright into a fire.

He envisions these walkingrobots “as being heat shielded, liquid cooled, with the operator asafe distance away, receiving video feedback. There could beseveral other robots in the area, all of them coordinated from a central command area where all ofthe video from the robots could beobserved.”

In the meantime, Owens continues building and refiningNMX041-A. “With this robot, I just decided that I wasn’t going to wait around for someone else to dothis; I thought that I had the knowledge and the ability, so I should

just do it.”Who knows? With a bit of luck

and lots of hard work, maybe he andNMX041-A will walk into history. SV

One possible application is fire fighting.

Take Control of an 18-Foot-Tall Walking Robot



Have you ever wanted to build a hex walker robot? Their interesting,

insect-like gait and seemingly complex leg construction make them one of

the more interesting projects in robotics. Hex walkers are actually more

accessible for the hobbyist than they may seem at first. In this series of articles,

I will show you, step-by-step, how to build a six-legged crawler using only

three servos, and with six legs and three servos,

we can experiment with different

gaits and full directional

control over the robot.

Next month, I will

discuss the electrical

construction of the

hex walker, and the

following month our

attention will turn to calibration,

programming, and control issues.

30 SERVO 03.2005

Simpson1.qxd 1/28/2005 11:41 AM Page 30

The ComponentsLet’s take a look at some of the

components needed to build thissmall walker.

The heart of the crawler is thesuper small, nine-gram Dragonflyservo (Figure 1). The small size ofthe servo lets us build an extremelysmall and lightweight robot. Thesetiny servos are very reasonablypriced at less than $9.00 each.

To control the small servos, we willuse the even smaller Perseus microcon-troller. I chose this microcontrollerbecause it has a very small 1.25 x 0.75inch carrier board (Figure 2) that cansport up to five servo connectors. Itsthrough-hole design makes it very wellsuited to the beginner. The Perseuschip, carrier, and RS232 driver boardcan all be purchased for less moneythan most other microcontrollers alone.

The Perseus microcontroller is one ofseveral Athena class microcontrollers thatwere designed to make the jump intomicrocontrollers as easy and inexpensiveas possible. The compiler software forthese microcontrollers is free and can bedownloaded from the Kronos Roboticswebsite at www.kronosrobotics.comThe software has a difficulty setting thatcan be adjusted from beginner to expertand has a simulator so you can runthrough the included tutorial withoutpurchasing a single item.

We will build the base and legs forthe crawler out of 1/8-inch Baltic birchplywood, similar to that shown in Figure3. You can pick up a 12 x 24-inch pieceat your local craft store for less than$5.00. That will be enough for four orfive robots this size. You will also needsome 3/8- x 3/8-inch pine stock as well,which can also be found at a craftstore for less then $2.00.

Probably the most difficultparts to get will be the hardware.Most of these will be #2 machinescrews and various washers andnuts. Kronos Robotics is offering apackage that contains all the hard-ware, as well as the 3/8 inch stock.

The ToolsFor the mechanical construc-

tion, you will need something to cutout all the wooden parts. I recommenda scroll saw. I did a complete write-upon various hobbyist level scroll saws inthe February 2005 issue of SERVOMagazine. The cuts are not critical, sothere are only a couple places wherereal accuracy is needed when cuttingout the parts. A hand coping or fretsaw and knife could also be used, but it will take you much longer tocomplete the project.

You will need a drill with 1/16-,3/32-, 1/8-, and 5/16-inch bits. I used adrill press, but a hand drill should workjust as well. A soldering iron (and solder)will also be needed to connect the twobattery holders and to build the Perseuscarrier board we’ll see next month. I alsorecommend a bit of heatshrink, too.

You will need a couple of handtools, such as a small Philips screw driverand a pair of needle nose pliers. Thesewill be used to tighten the small locknuts, as this can’t be done by hand.

In Part 3, we will start program-ming the walker. For this, you will needan EZ232 driver (less than $10.00) anda copy of the compiler software (freefrom the Kronos Robotics website). APC running Windows and nine-pin serial cable will also be needed.

The PlansI have included a full-size set of

plans for all the cutout parts. You can download them from the SERVOwebsite (www.servomagazine.com).There are index marks on the plans, so you will be okay as long as yourreproduction is set to the proper size.

When enlarged or reduced, thedistance between Index A and Index Bshould be five inches. The distancebetween Index A and Index C shouldbe seven inches.

MechanicalConstruction

Now, we come to the fun part.Let’s start building the walker. Beforewe begin, let me say a few thingsabout this design. I designed thiscrawler with three things in mind:

• Repeatability — I wanted a walkerthat could be built consistently; it could

Part 1

FIGURE 11. The super small, nine-gramDragonfly servo.

FIGURE 22. The Perseus microcontroller.

FIGURE 33. A 12 x 24-inch piece of Baltic birch plywood works best for the base and the legs.

FIGURE 44. The final cuts.

SERVO 03.2005 31


32 SERVO 03.2005

The Mini Servo WALKER

be built by 20 different people but stillbehave the same.

• Construction Forgiveness — I wanteda walker that could still function even iferrors in construction were made.

• Cost — I wanted a walker that couldbe built completely for under $70.00 —even less if you have some of the partsin your junk box.

The mini servo walker design isvery forgiving, as most of the cuts arenot critical. In fact, variations in thepieces will give your walker a bit ofcharacter. For instance, rounding thecorners on the walker base will makethe walker a bit more bug-like.

Hole placement should be as closeas possible to what is detailed here, butas long as you are within 1/32 inches,you should be fine.

Step 1:Cut out all the parts in the plan.

Note that some parts require morethan one cutout. For example, you willneed four Leg A parts and four Leg Bparts. You will need two Leg C parts.

The Rear and Center Leg Supportsare both cut from a 3/8- x 3/8- x 2-inch

piece of stock. They canbe cut from pine, bass-wood, or maple — all ofwhich are available atyour local craft store.Place the template forthe Rear Leg Supporton the stock and mark

the two holes.For the Center Leg Support,

bend the template in half wherethe top view and bottom viewcome together and place on thestock as shown in Figure 5.

The most critical cut of all isthe thickness of the notch,shown in Figure 6. The actualthickness of the notch shouldmatch the thickness of the ply-wood stock you are using. It can

be a bit smaller, but not larger; therefore,I recommend that you cut it a bit small.You can increase the width, if needed.

Make sure you place a small notchin the center legs, as shown in Figure 7.This notch will be used later to hold theend of a small rubberband.

Step 2:Attach the two center legs to the

Center Leg Support, as shown in Figure8. Use two 3/4-inch #2 machine screws.Install in the following order: #2machine screw, #2 washer, Leg C, #2washer, Center Leg Support, #2 washer,and #2 lock nut. Make sure you installthe two 3/32-inch holes. Tighten so thatthe legs are seated firmly against thesupport, but still move freely.

Step 3:Install the two servos into the servo

slots shown in Figure 9. The 1/16-inchholes in the base will act as our nuts andhold the machine screws nicely. Use 3/8-inch #2 machine screws and #2 washerson each hole. You will have to push thescrew firmly to get it started. Don’t over-tighten or you will strip the wood. Youcan also attach a #2 hex nut, as well.

Step 4:Take the Center Leg assembly and

FIGURE 55. Wrap the Center Leg Support templatearound the stock as shown here.

FIGURE 66. The thickness of the notch cuts are most critical.

FIGURE 88. Attach the Center Legs to the Center Leg Support.

FIGURE 77. A small notch is needed at the end of the Center Legs to hold a small rubberband.

FIGURE 99. Attach the servos, the Center Leg Assembly,and the Rear Leg Support and Legs.


attach it to the base, as shown in Figures 9 and 10. You willuse two 3/4-inch #2 machine screws. Attach in the followingorder: #2 machine screw, #2 washer, base, #2 washer, and#2 hex nut.

The 1/8-inch holes are oversized so that you can positionthe support as needed. Make sure the legs move freely anddon’t rub against the base. Tighten the nuts.

Step 5:Install the Rear Leg Support and Legs as shown in Figure

9. Use two one-inch #4 machine screws in the followingorder: #4 machine screw, #4 washer, Leg Part A, #4 washer,Rear Leg Support, base, #4 washer, and #4 lock nut.

Tighten so that the legs are firm, but rotate freely.

Step 6:Take two of the four-sided servo arms and drill a 1/16-inch

hole as shown in Figure 11. The 1/16-inch hole is just a bitsmall for the #2 machine screws; this allows the plastic to actas a lock washer once the arm is attached to the leg.

Step 7:Take the servo arm and center it on the 1/8-inch hole

and mark the four holes you drilled in Step 6. If you insert thesmall screw used to attach the servo arm to the servo, it willhelp you center the arm. Please note that if the arm is not100 percent centered, it won’t affect operation at all.

You will need to do this with the two remaining legs.Step 8:

Drill four 3/32-inch holes into each leg. Insert four 1/4-inch

Part 1

FIGURE 110. The underside of the Center Leg Assembly.

33Circle #82 on the Reader Service Card.

FIGURE 111. One of two four-sided servo arms.

FIGURE 112. Drill four additional3/32-inch holes into each leg.

FIGURE 113 aand 114. Use 1/4-inch machine screws and nuts to attach the servo arm to each leg.

FIGURE 115. One side of the Dragonfly servo arm.

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The Mini Servo WALKER

#2 machine screws and attach theservo arm to the leg as shown inFigures 13 and 14. Use a #2 hex nut tohelp hold the screws in place.

Step 9:Take one of the two-sided

Dragonfly servo arms and snip off oneside, as shown. Make two snips at aslight angle so you don’t put too muchstress on the arm when you cut it.

Step 10:When using micro servos, we some-

times must make special provisions formounting due to size or construction.The Dragonfly servo is held togetherwith a small plastic band and a smalllabel. This prevents us from mountingthe servo reliably using mounting foamtape. To correct this, we simply removethe clear plastic label (tape) and the plastic band. We then take a piece ofmetal air conditioning tape and wrap theservo, as shown in Figure 16.

We must also remove the leftmounting flange from the servo as it

comes in contact with the Center LegSupport mounting screw. Place the armon the servo so that it points straight upin the orientation shown in Figure 17.Don’t worry about the current servoposition, as we will calibrate later.

Next, position the servo as shown sothat the arm is dead center of the twocenter legs. Do a dry fit, then add a pieceof mounting foam tape and position it inplace. You can pick up some double-stickfoam strips at any department or homestore. Don’t use the removable type. Irecommend a name brand, as it’s muchfirmer and holds the servo better.

Place a small rubberband acrossthe top of the two center legs. The rubberband will cause the leg notbeing pushed down to lift up. The bestplace to pick up rubberbands is in thehair care section of a store. (Thesesmall rubberbands are used to makesmall pony tails.)

Step 11:Attach the front legs you completed

in Step 8. Now, you may also attach the

lower legs to all of theupper legs by insertingthe notches into eachother.

Step 12:Now, attach the

Rear Leg Drive, asshown in Figure 18.The leg drive is used tomove the rear legwhen the front legmoves. Use a 1/2-inch#2 machine screw in

each leg in the following order: #2machine screw, #2 washer, leg drive, #2washer, leg, #2 washer, and #2 lock nut.Tighten enough to remove the wiggle.

Now, attach the lower legs if youdid not already do so in Step 11. LegParts A and B are held together by friction. If you cut the slots too wide,they may not hold together; you mayneed to apply a drop or two of hotglue to strengthen the joint.

This concludes the mechanical construction phase. Go ahead andinsert the small screws that came withyour Dragonfly servo into the servoarms and tighten them. This will holdthe legs in place until we are ready tocalibrate. You can also run the twofront servo connectors up through the5/16-inch hole. Take the center servoconnector and run it around the side,then back up through the 5/16-inchhole from the bottom.

At this point, you have a completewalker eagerly waiting for its powersource and brain. Next month, I willshow you how to install these. Here aresome things to check while you areanxiously waiting for the next issue ofSERVO Magazine:

• Make sure all joints with lock nuts arenot too tight. The piece should movefreely, but not wiggle.

• The upper and lower leg joint shouldbe firm and should not wiggle.

• The center servo should be securelyattached to the base and should notmove in any direction. If it does, thefoam tape you are using is too thick. SV

34 SERVO 03.2005

FIGURE 116. Wrap theservo motor in metal tape.

FIGURE 117. Remove the leftmounting flange on the servo.

Qty Description Source and part number3 Dragonfly 9-gram servos http://stores.channeladvisor.com/rc

toys-hobbies/Items/400010?

1 12 x 24 sheet or 12 x 12 sheet Can be purchased at most craft or hobby of 1/8-inch Baltic birch plywood stores. It can also be purchased from

Woodcraft at www.woodcraft.comin 12 x 12 sheets.

1 Hardware package. Contains all Kronos Robotics at mounting screws, washers, and www.kronosrobotics.comlock nuts. Also includes two3/8 x 3/8 x 2-inch pine blocks for legsupports. One piece of heatshrinktubing. Includes metal tape andmounting foam. Printed pattern sheet.

Sources

FIGURE 118. Here is the completewalker awaiting its brain.


SERVO 03.2005 35

by J. Wolfgang Goerlich

The Eastern Canadian Robot Games

(ECRG) are held each fall at the Ontario

Science Centre in Toronto. Teams from all

over North America come to compete,

including Canadians from as far away as

Alberta and British Columbia, Americans

from Tennessee to Texas, and teams from

Mexico. This year saw robots from England

and Iran, too. Over 80 robots competed in

events as diverse as BEAM, sumo, and fire

fighting.

Goerlich.qxd 1/28/2005 4:12 PM Page 35

BEAM EventsToronto has long been a hot spot for BEAM robotics,

thanks in large part to the regular BuildFests at Bug ‘n’Bots. In Solaroller, contestants race solar-powered vehicles.Turtle, a robot hailing from England, could complete thecourse in mere seconds and was easily the fastest of the day.

There was a sneak peak at the rule books for next year’s Photovore event. ECRG is encouraging solar-poweredmicro-sumo and nano-sumo-size competitors, with no limiton the size of the solar cells. The format will be a day-long exhibition, where participants can enter up to four solar-powered robots and have them compete together in swarmsor teams. Judging by these rules, ECRG 2005’s Photovore willbe a lot of fun.

Full-Sized SumoThe number of bots keeps growing in the full-sized sumo

competition. There were not enough robots to run the competition in the game’s first year, but this year, there werearound 10 robots competing. Mark MacKenzie, who had

brought a full-sized sumo, chose to compete against theremote-controlled sumos, and in a true match of man againstmachine, Mark’s sumo won the day.

Two of the robots in this class were brought in by teams from Iran. Aabed Naseri brought Sepanta, while the Islamic Azad Saveh University ran their IAUS sumo, which took third place. First place went to Phantom, DaveHylands’ sumo, based on the Lynxmotion Viper, and SpaceJunk, a scratch-built bot by Lee Szuba, took second.

Master’s Mini-SumoThe Master’s mini-sumo competition is open for magnetics,

and the robots are under the same size and weight restric-tions as the regular mini-sumo competition (10 cm2 and 500grams, respectively). In past years, this has been a contest tobeat Dave Hylands, as he regularly brings with him severaltop contenders to this match.

Because of Grant McKee’s Ender’s Wraith, theMaster’s was different this year. Ender’s Wraith arrived atECRG fresh from winning at the Western Canadian RobotGames and at Robothon; it also took second place atROBOlympics and PDXbot. Grant’s mini did it again, taking

Fred and Ugly compete in the traditional BEAM Photovorecompetition. Next year, these robots will be returning

for a new exhibition event.

Tom Gray’s Four Eyes faces down Copy Cat by Kyle Simmons.Four Eyes is a modified Sumovore with a rear IR sensor

system. Copy Cat was a scratch-built mini with a transplanted Sumovore sensor board.

Phantom vies with Space Junk for first place in theFull-Sized Sumo class.

This year’s Master’s mini sumo champion was Ender’s Wraithby Grant McKee.

36 SERVO 03.2005


SERVO 03.2005 37

first at this year’s games, while Dave Hylands’ Maraudertook second place.

One of the fun moments came when the judges pittedEnder’s Wraith up against the winners of the full-sized sumocompetition. So, how did the 500 gram Master’s championfare against the winners of the 3 kilogram class? Ender’sWraith took them down.

Open Mini-SumoSince the Solarbotics’ Sumovore arrived on the scene, it

has dominated ECRG’s open mini sumo category. This yearwas much the same, with the majority of the minis beinghacked Sumovores. The hacks ran the gamut from upgradedsensors to souped-up motors to pipe-cleaner antennas. Inthe end, team WoloBot took first place with their modifiedSumovore.

Of course, there were plenty of scratch-built minis, too. One of the more powerful ones was Harm’s Way II, built and piloted by Eliot Barker on the “Wreck the Bed”team. The drive train was comprised of two SolarboticsGM9s, modified with Qjet speed 200 motors from Gold Scallop. This gave it plenty of power. One fine example

of this was when Harm’s Way II lost the match and it promptly turned around and attacked the sumo ring. Harm’sWay II pushed the ring — along with the offending mini sumo— some distance before the judge stepped in.

Line FollowingLine following is a classic robot competition, and there

are always a handful of mini sumos that cross over to com-pete. Perhaps not surprisingly, this is a competition regularlydominated by Dave Hylands and Marauder. This year, GrantMcKee took it up a notch by designing a particularly toughcourse.

Truffle Pig, built by Nicholas Barker of Team “Wreck theBed,” stole the show. Truffle Pig features a microcontroller,sensor, and drive subsystems based on the SolarboticsSumovore.

However, it was much, much lighter than a Sumovoreand was using the faster GM10 motors. Not only did it takefirst place, but it also completed Grant McKee’s course with

Harms Way II by Eliot Barker is the scratch-builtmini that took on not only the competition,

but the ring it was competing on.

Bug ‘n’ Bots and Solarbotics held walker workshops prior to theGames. The result of these workshops was that the new

ScoutWalker III kits swarmed the walker event. Joe Garcia’sScoutWalker IIIs took first, while Leah Mitchel’s took third place.Ant, the scratch-built walker by students at Malvern CI,

took second place in the walker competition.

Truffle Pig by Nicholas Barker features Solarbotics GM10 motors and a microcontroller, sensor, and drive subsystem based on the Solarbotics

Sumovore. It took first place in line following.


38 SERVO 03.2005

only a single pick-up. Of course, it helped that Nicholasprimed the audience by handing out Truffle Pig temporarytattoos. The calls of “Go piggy!” during the last run werevery entertaining.

WalkerThe students at Malvern — the returning champions from

2003 — had a tough competition cut out for their Ant Walker.The Solarbotics ScoutWalker IIIs were out in droves at thisyear’s competition, and lucky for Malvern, ECRG changed thewalker competition and adopted rules based on the PDXbotwalker contest. The speed points are awarded using

Alexander’s Formula.This meant that Ant had a natural advantage because of

its shorter legs. Indeed, the competition for first place wasclose between Ant and Joe Garcia’s ScoutWalker III, with Antonly losing on the last run when it became tangled up in thecarpeting.

Wellhead BlowoutThe ECRG Wellhead Blowout is a competition along the

lines of the Trinity College Fire Fighting contest. Robotssearch a maze for a candle and extinguish it, getting pointsfor starting with a sound, for completing with the bestspeed, and for returning to base. This is always a good showof innovative approaches.

That sums up this year’s Eastern Canadian RobotGames. To find more information on next year’s event andwhat you missed out on at this year’s competition, visitwww.robotgames.ca SV

Grand Valley State University has a history of buildingfire-fighting robots, sych as Gromit. This year they brought

out their new one – Flamebait.

“Bruce Sheridan’s robot, Flameout, was constructed from LEGOpieces. It had less sensors than many of his other competitors,

but used an innovative strategy of having a square base on therobot that backed up to a wall after each turn, which correctlyoriented Flameout to run perfectly parallel to the walls. Even

though his robot was almost blind compared to the other robots,he earned a fourth place finish.” — John Edwards

“Chris Wardell’s robot Xtinguisher ran extremely smooth and precise to gain him a second place finish. While all other fire

fighters were here in Toronto testing and tuning on Saturday,Chris was still programming back in Ohio. He arrived in Toronto

at 3 A.M. Sunday morning. When he got ready to run a few testrounds Sunday morning, he discovered Xtinguisher would

do nothing. As it turns out, a wire shaken loose in transport was discovered and corrected just in time for a few test runs

and competition.” — John Edwards

The Eastern Canadian Robot Games are held in the ScienceCentre’s Imperial Oil Room. The spectators bring a lot

of energy to the events.


SERVO 03.2005 39

Every robot builder knows that the visual aspect of your robot is half of its appeal. With that in mind, I decided to build a robot to recall the one that got many of us

interested in robotics to begin with: Star Wars’ R2-D2.This project details the construction of a mobile robot in an R2-D2-like case, and to it

I applied several lessons learned from previous robot construction projects. The platformhas two independently driven wheels and two casters. The head of the robot — containingmost of the sensor package — rotates. Two PC-class computers are onboard, operating onthe onboard 12-volt batteries, and the robot is linked to a wireless network. The PCs provide a layered architecture, ease-of-use, and reasonable power draw, while the overallproject combined aspects of digital and analog design and programming and involvedabout two years of on-and-off work.

byPat Stakem

Stakem.qxd 1/28/2005 11:33 AM Page 39

Hardware DetailsThe robot platform consists of a

wheel assembly and base which mountson a shell. The shell and structure are anAmerican Toy & Furniture toy box witha Star Wars theme licensed fromLucasfilm. It is an 18-inch-tall cylinderthat is 16 inches in diameter with ahemispherical, molded plastic head.The drive is provided by dual Brevel +36volt, permanent magnet gear motors(model 790-1953075) with seven-inchwheels. A 12 volt Brevel motor (model

105-82/001) is used to rotate the head,and power is supplied by dual 12-volt,7.2-amp-hour, gel-cell batteries byPowerPatrol (model SLA1075).

The entire unit weighs 45 pounds— excluding the batteries — which addanother 10 pounds. The robot is aboutthree feet tall and 21 inches wideacross the wheels. Two casters, mountedfront and back, provide stability to theplatform. The motors are mounted in awooden frame that is attached to an18-inch diameter plywood base.

For embedded control, two PC-class machines are used — one in thehead and one in the body — and theadvantages of using the PC platform arethe standardized interfaces it providesand the availability of a wide range ofoff-the-shelf hardware and software.

The head computer consists of a386sx-40 mini motherboard with four-by-30-pin SIMM memory slots and an ISAbus for a serial/parallel board, VGAboard, and floppy disk controller/hard

disk controller card. It can use a standard3.5 inch, 1.44 megabyte floppy drive andIDE-based hard drives and CD drives. Intypical configuration, the board drawsone amp at five volts, with fourmegabytes of memory. It operates froma single 12-volt input power supply.

The head computer interfaces withthe sensors to minimize the amount ofwiring passing through the rotatinghead to body interface. Monitoring thebattery voltages and, eventually, thecurrent draw of the motors can best bedone closer to those units by the bodycomputer. The head computer to bodycomputer data connection is via a LANusing an onboard hub.

The body computer — a Pentium200MMX — has both a PCI and an ISAbus, and it can use either the 72-pin or168-pin SIMM memory. A dual serialand a parallel interface are provided onthe motherboard, as is USB support.The circa 1997 AWARD BIOS supportsmonitoring of the CPU temperature.The board uses the I430TX chipset. In atypical configuration, a 64-megabytemodule of 168-pin memory is employed

40 SERVO 03.2005

R2-D2: A PC-Powered Mobile Robot

FIGURE 1. The complete unit.

FIGURE 2. The molded plastic headassembly. The Polaroid ultrasonic sensoris visible. The ball at the top of the head

is for the video camera.

FIGURE 3. The head computer. Thepower converter is on the right. The

bracket in foreground is for a hard disk.

FIGURE 4. The head rotation motor isattached to the bottom of the head

mounting plate.

1. The game interface on the sound card isa simple A/D circuit. Normally used with ajoystick, it expects to see a 100K ohmresistance and supplies voltage and acapacitor to form a timing circuit.

2. We hook up a 100K ohm thermistor tothe game connector.

3. The Logo command is:

SHOW INGAMEPORT 1

This displays “counts.”

4. We calibrate the sensor using ice waterfor a low limit and ambient temperature.

5. Using the derived cal curve, we cannow display the temperature in °F. The curve is mostly linear over theexpected range of temperature.

SHOW 32 + .024 * INGAMEPORT 1

Reading Temperature With logo


SERVO 03.2005 41

with a Cirrus 5446 SVGA PCI videocard, a sound/game card, a 3.5-inch,1.44-megabyte floppy, a CD, and afour-gigabyte hard drive.

The board has been tested withboth USB and parallel interface webcams and supports a 16-bit protocard inthe EISA bus. Wired (Realtek 8139) andwireless (802.11b) network connectionsare included. The body computer uses astandard chassis, shortened by 1-3/8inches to fit within the body shell. Thisonly affected the use of long EISA cards— such as the protocard — which had tobe trimmed to length.

Both computers may be attachedto a keyboard, mouse, monitor, and awired network connection when therobot is on the workbench. Also, bothcomputers can boot without having akeyboard attached. When connected toa network, the PC-Anywhere program isused to access the robot computers froma PC. The CPU in the body computer wasover-clocked to 225 MHz, but was notreliable at that frequency and wasreturned to its nominal clock value.

The power amplifier for the motordrive module is a unit that was devel-oped and has been in use for over 10years at Loyola College (where I teach)for an Introductory Physics Lab Programin robotics. The board measures sevenby four inches and is dual channel. Ituses an analog input and was originallydesigned for use with servooperated potentiometers. Themotor drive section uses2N6286 and 2N6283 powertransistors, and to drive themotor amp from the computer,we need a link between thedigital and the analog world.Various D/A options were considered, such as the Maxim505 and MAX7228 chips. AD/A card would require a cus-tom device driver to the controllanguage (Logo) and a simplerapproach was adopted.

The critical tie betweenthe digital world of the computer and the analogworld of the motors is providedby a cheap-and-dirty, dual,four-channel digital-to-analog

board operating off of the parallel(printer) port. The eight-bit output ofthe parallel port is split into two four-bitsections, each providing a signed three-bit (eight level) code. This is more thansufficient for the motor control.

A simple ladder network convertsthis to an analog voltage between zeroand five volts. This is level shifted andamplified by a 741 op-amp to a ±12-voltsignal and is applied to the input of the motor driver. The D/A board isequipped with a disk drive power con-nector and is supplied by +5 and +12volts from the computer. The -12 volt-age is derived via a Maxim 7662 chipfrom the +12 volt line. The Maxim chiprequires only two electrolytic capacitors.

The motor driver board is mountedon a piece of plastic to the left side ofthe body computer chassis, along withconnections for power and motor wiringand the fusing. The A/D board is mountedbeside it and connected to power andthe parallel port of the body computer.

A manual control pendant is providedto move the robot in a tethered mode.This handheld control box has threeswitches and LEDs are used to indicatepower. The left and right motors are controlled independently with center off,momentary switches, while the thirdswitch controls the head rotation. ADPDT switch at the bottom rear of therobot selects either manual or computer

control of the motors. In March 2002, Ireached a milestone and completed aversion of the robot where the headrotated and the drive motors turned.Computer control of the drive systemwasn’t achieved until November of 2004.


FIGURE 5. Side view of the computer.The power supply is modified to work

from 12 volts. The battery is in the foreground.

FIGURE 6. The motor amp is mountedon the red plastic piece, along withfusing and power distribution. The

prototype parallel port A/D card is onthe right, connected to the computer’s

parallel port. The battery has beenremoved for visibility.

FIGURE 7. Drive motors in their frame.

1. Use consistently color-coded wire.2. A main power switch would be nice, along with abig red emergency stop button.3. Include an onboard battery charger.4. Rapid prototyping in both hardware and softwareis the key to success.5. Robotics is certainly getting easier.

Lessons Learned


SensorsMost of the sensors are built into

the rotating head, as there is a bracketfor a Garmin GPS-38 receiver with aserial interface. The head assembly haslight sensors, a Polaroid ultrasonicrange finder, dual audio sensors(dynamic microphones), and the webcam. The two microphone “ears” oneither side of the head can be broughttogether into an analog multiplexerand an A/D. A similar set-up on an

earlier Hero robot compared sensorreadings and implemented binauralhearing by centering the head on thesound source. Another useful feature isa computer “heartbeat” indication: asignal to indicate the computer is stillworking and not hung. This might beas simple as an LED that is flashed onceper second under program control.

Architectural ControlModels

The robot’s body computer acts asthe servo level of control, interfacing withsensors and actuators. It also provides anintermediate level of control. Additionalcomputational resources can providehigher levels of goal seeking control tothe system via the wireless connection.This follows the general principles of the

NASREM model — based on work atNIST and NASA — and the FlightTelerobotic Servicer Project.

This next higher level is the supervi-sory level, which decides what to do.Above that level and implemented exter-nally to the platform is the world model.

Via the wireless Internet, the bodyCPU is online to four other machines,including a storage server with a DVD drive. This allows for the off platform allocation of computationaland storage resources to robot tasks.

The Logo system running on the MZ-104 presents an abstraction layerbetween the user and the underlyinghardware at the servo level. The details ofthe servo level are hidden. The user doesnot operate at the “brain stem” level, butrather at the “cortex” level with goalsand schema, not control and status bits.

Design ConstraintsThe computers in the robot need to

operate from battery power, have mini-mum power draw, minimize their heatproduction so that fans are not required,and be tolerant of a vibration environ-ment (as the robot has no suspension).

A laptop computer might seemideal for the application of the bodycomputer, as they are designed tooperate with battery power and are

42 SERVO 03.2005


FIGURE 8. Manual control box. Thisplugs into a connector at the rear of therobot, where there is a switch to select

manual or computer control.

FIGURE 9. Safe robotics.

Stakem, Patrick H. and Hynes, Shane“Sensors for Robots, the Integration ofSensed Data, and Knowledge-BasedNavigation Systems,” International PersonalRobotics Conference-1, Albuquerque, NM,April 1984.

Everett, H. R., Sensors for Mobile RobotsTheory and Applications, Natick, MA: A. K.Peters, Ltd., 1995 ISBN 1-56881-048-2.

Dudek, Gregory and Jenkin, Michael,Computational Principles of MobileRobotics, Cambridge University Press, ISBN0521568765.

Stakem, Patrick H. “Use of Zero-powerRAM for Personal Robots,” RobotExperimenter Magazine, August 1985.

Medeiros, Adelardo A.D., “A Survey of

Control Architectures for AutonomousMobile Robots,” Abstract 1988, J. BrazilianComputer Society, v.4 n. 3

Stakem, Pat, Lumia, Ron, and Smith, Dave,“A Computer and CommunicationsArchitecture for the Flight TeleroboticServicer,” June 24, 1988, ICG-#20,Intelligent Controls Group, RobotSystems Division, National Bureau ofStandards.

Stakem, Patrick H. “The Brilliant Bulldozer:Parallel Processing Techniques forOnboard Computation in UnmannedVehicles”, 15th Autonomous UnmannedVehicle Systems Symposium, San Diego,CA, June 6-8, 1988.

Papert, Seymour MindStorms, Children,Computers, and Powerful Ideas, 1980,

ISBN 0465046746.

MSW Logo — see www.softronix.com/logo.html

Martin, Fred and Silverman, Brian, “TheHandy Logo Reference Manual,” January12, 1996, MIT Media Lab. http://cs.wellesley.edu/rds/handouts/HandyLogoReferenceManual.pdf

Mini Book Robot White Paper, December2002, Evolution Robotics, www.evolution.com

AmigoBot User’s Guide, ActivMediaRobotics, v. 1, November 2002,www.amigobot.com

Open Source Motor Controller Project —see www.robot-power.com/

Further Readings and References


small and light. The main disadvantageis the cost, due to the built-in screen.Secondhand units with broken displayscan sometimes be purchased inexpen-sively and used with an external monitor,when necessary. However, the laptopcannot take expansion cards without aspecial docking station accessory. Later,we will discuss new and emergingboards that are even better suited tothis application than laptops.

SoftwareThe operating environment is

Windows-98SE (a 200-megabyte diskfootprint) with the PC-Anywhere program, Delorme mapping, iSpeak,and various other utilities. There is custom wallpaper on the backgroundwith a picture of the robot itself.

The Logo programming languageis ideal for robot control, as it containsconstructs for moving and turning. Theproblem has been the lack of decentI/O in implementations, but this isaddressed in the MSWLogo distribu-tion. This language was applied in aprevious project to update a Hero, Jr.robot with an added single chip PCprocessor. This used Logo under theLinux operating system in a metapro-gramming mode — the Logo programwrote programs for the embedded con-troller on the fly and downloaded themvia a serial connection for execution.

Future DirectionsFirst, I want to expand the sensor

suite. Bart Everett’s book (see the“Further Reading” sidebar) is the defini-tive guide to a robotic sensor platform.Many of these parts are now sitting in abox, waiting for available bench time.These include tilt sensors, an infraredmotion detector, a smoke detector, bumpswitches along the base, and a digitalcompass chip. I also need to completethe onboard battery charger, which willcharge both batteries from wall power.

In spite of its appearance andbecause there are no manipulators, wemight term this initial unit “R1-D1.”Interestingly, I have three of the cases,so construction of a second unit is

already underway. We might term this“R1-D2.” It will incorporate lessonslearned from the first construction, aswell as advances in technology. The second unit will utilize a radio controlmanual mode. This is already implement-ed on the motor driver card and only asingle computer will be used. This neces-sitates “spinal cord” wire managementthrough the rotating head interface, butthe wiring will be minimized and headrotation will be arbitrarily limited.

The computer will be a mini ITXform factor from VIA. These mother-boards are 6.75 inches square andincorporate built-in video and LAN. Atransition from Windows to Linux isenvisioned, as Linux is the ideal operat-ing environment for the robot computersystem. With Linux, you can control thesoftware components in the system build by including only thosecomponents you need. The real-timebehavior of Linux is better and exten-sions allow true real-time performance.Many of the newer Linux distributionsare getting “fat,” mostly due to theGUI. Slimmed down systems — such asVectorLinux — show promise, and support for devices such as USB connect-ed cameras and wireless networking are

now standard. Berkeley Logo — whichruns under Linux — is the basis for theMSWLogo used in this project.

Several off-the-shelf manipulators(hand and arm assemblies) are nowavailable for a reasonable cost. Theseenable a new series of capabilities. Ienvision a robotic debug assistant thatcan store and display schematics as pdffiles, incorporate a digital voltmeter,digital logic analyzer, and oscilloscopeand integrate these with speech.

I already have a serial-to-CAN-businterface cable and the software toallow a PC to read the onboard computerin the car. Perhaps the robot can be acar mechanic assistant, as well. SV

SERVO 03.2005 43


FIGURE 10. Screen shot.

Patrick H. Stakem is a senior systemsengineer and teaches at Loyola College’sGraduate Computer Science Program. Hewas the Principle Investigator for NASA’sFlightLinux Project and supported theFlight Telerobotic Servicer Program, arobotic element of the Space Station. Hehas a BSEE degree from Carnegie-Mellonand MS in Physics and Computer Sciencefrom Johns Hopkins. He has been active inrobotics for over 20 years.

About the Author


µµM-FPU V2 Floating PointCoprocessor

Micromega Corporation is offering a new versionof the µM-FPU

Floating PointCoprocessor. The newversion — µM-FPU V2 —now supports both I2Cand SPI interfaces. TheI2C interface supportsbus transfers atspeeds up to 400 kHzand the SPI interface sup-ports speeds up to fourMHz. A 32-byte instruc-tion buffer has beenadded for improved throughput and easier inter-facing. Several new instructions have been added,including new data transfer instructions, 32-bit integerlogical operations, conditional execution, table look-ups,and Nth order polynomials.

The µM-FPU interfaces to virtually any microcon-troller using either an I2C or SPI interface, making itideal for applications requiring floating point math, such as converting sensor readings, robotic control,data manipulation, and other embedded control applications.

The µM-FPU provides support for 32-bit IEEE 754 com-patible floating point operations and 32-bit integer opera-tions. A PIC compatible mode is also available to supportPIC format floating point numbers. An extensive list offunctions are built in, including floating point math, longinteger math, exponential functions, trigonometric func-tions, data conversion, and formatting functions. A built-in debug monitor is available to assist in developing anddebugging code.

A unique feature of the µM-FPU is the ability to defineuser functions. User functions are defined as a series ofbuilt-in operations and are stored in Flash memory on theµM-FPU chip. Since they are stored internally, the majorityof communications overhead is eliminated. This results indramatic speed improvements and greatly reduced codespace requirements on the microcontroller. Software isprovided to define user functions using standard math

expressions and to program the µM-FPU over a RS-232connection.

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For further information, please contact:

Orangutan Robot Controller

Pololu has intro-duced the

Orangutan robot con-troller, a complete con-trol solution for smallrobots. Orangutanincludes an eight-char-acter x two-line liquidcrystal display, two bi-directional motor

ports, a buzzer, threepush-buttons, and up to 12 user I/O lines, yet the com-pact module measures only 2.00 x 1.85 inches andweighs less than one ounce. Because of the complete fea-ture set, very few additional components (such as sensorsor motors) need to be added to complete the electronicportion of a small robot. The small package allows forgreater flexibility in incorporating the electronics into themechanical design of a robot.

Orangutan is based on the Atmel MEGA8 microcon-troller, which features eight Kbytes of Flash programmemory, 1,024 bytes of SRAM, and 512 bytes of EEP-ROM. Up to eight channels of 10-bit analog-to-digital con-version is also available. Because the user has directaccess to the microcontroller, any development softwarefor Atmel’s AVR microcontrollers — including Atmel’s freeAVR Studio and the GCC C compiler — is compatible withOrangutan. An in-circuit programmer — such as Atmel’saffordable AVR ISP — is required for programmingOrangutan. For applications requiring more programmemory, the MEGA168 microcontroller with double the program space can be substituted for the MEGA8

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44 SERVO 03.2005

MarNewProducts.qxd 2/3/2005 3:25 PM Page 44

microcontroller.The Orangutan input voltage is

5-10 volts, making it well-suited foruse with small DC motors and five- toeight-cell NiCd or NiMH batterypacks. The motor driver can supplyup to a maximum of one A per motorchannel, subject to power dissipationrequirements. Total power consump-tion (with motors and buzzer off) isunder 15 mA.

The unit price for the fully assem-bled and tested Orangutan robot con-troller is $79.00, with free shipping inthe US.

For further information, pleasecontact:

Robot Kit forEducation and Hobby

Swope Designs, Inc., announcedBalBot™ — the first ever low

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The thrust behind BalBot is tonot only provide a robotic platformfor inventors, researchers, and stu-dents, but to do so in a way thatevokes a new level of creativity, moti-vation, and excitement from the user.With its innovative technology andform factor, BalBot is designed toinspire and free users to build uponthis platform to produce their owningenious creations. Why build a “standard” robot when you canbuild one that’s more fun andmaneuverable?

BalBot is available in two differentkits. The BalBot Basic™ and BalBotAdvanced™. The BalBot Basic providesan active balancing platform — com-plete with real-time balancing controlcircuitry — and is ready for the user toadd a microcontroller (if navigation isdesired).

The BalBot Advanced adds for-ward-looking sensors and a full-fea-tured microcontroller board completewith LCD display, serial communica-tions, expansion ports, programmer,open source C compiler, and samplecode. Both kits come complete; only ascrew driver and batteries arerequired.

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Show Us What You’ve Got!

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For the finest in robots, parts, and services, go towww.servomagazine.com and click on Robo-Links

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46 SERVO 03.2005

RobolinksMar.qxd 2/3/2005 1:33 PM Page 46

SERVO 03.2005 47

WowWee, Ltd., rocked the house at the Consumer Electronics Show

(CES) 2005 in Las Vegas, NV. The toy shop behind the Robosapien family

of entertainment robots unveiled five spectacles of modern technical

innovation, three of which we will take a closer look at.

Sapiens and Doggies and Raptors, Oh My!

by DDavid GGeer

GeerFeature.qxd 1/28/2005 4:51 PM Page 47

Robosapien2 and Friends —Playful? Practical?

The next iteration of Robosapien — Robosapien2 — is alsoa toy, yet it’s bigger and more capable than its predecessor.More an example of total evolution than slight improvement,Robosapien2 stands 24 inches tall — a full 10-inch gain overhis older brother. He can lift, throw, and drop with his muchlarger, four — not three — fingered hands. Yes, Robosapien2has three fingers and an opposable thumb!

More ‘Sapien-like all the time,Robosapien2 can sit, stand, liedown, and get back up. Extramotions that help to facilitate thesebehaviors include bending over andtwisting at the waist.

Robosapien2 can detect andavoid obstacles, track movement,and grasp objects that are given tohim. He does this with the aid ofhis infrared, radar vision eyes. Hecan also tell objects from humanflesh via his built-in vision color system. These talents enableRobosapien2 to wave when he recognizes someone or to respondwith a handshake.

Robosapien2 can hear and talkup a storm. His stereo sound detec-tion system enables him to respondto the surrounding auditory envi-ronment. Laser tracking capabilitiesenable him to follow a path, whichyou can trace on the floor with a

laser that comes in the remote control unit.Robosapien2 can guide his new WowWee robot

companions — Robopet and Roboraptor — and interact withthem. Robosapien2 is due out in September ... along with hisfriends.

RobopetWith a build and ears comparable to those of a Basenji,

Robopet is your high energy dog-tronic playtime friend. He has several lively, interactive sounds and animations in

Robosapien2 CComes tto LLife WWith DDomestic aand PPrehistoric CCompanions

“My, wwhat bbig hhands yyou hhave?!” “The bbetter tto ffetch yyour bbeverage wwith,

my ffine rroboticist ffriend.”

How mmuch iis tthat ffinely ttuned,alien-eeared ddoggy iin mmy ccamera llens?

(Hint: LLess tthan aa ddog ffrom tthepound wwith aall iits sshots.)

48 SERVO 03.2005

All the intel we could squeeze out of the WowWee grapevine is that there areadditional generations of the products in development now. Judging by current year-to-year progress, might we see a four-foot Robosapien3 in 2006? Might it havehundreds of programs and capabilities? Might it become fully autonomous? Willadvanced versions of Robosapien cross over from toys to tools, doing chores andworking side-by-side with human masters? Stay tuned as these and other questionsare answered in future versions of WowWee robots.

WowWee AliveThink WowWee only has Robosapiens? Not by a long shot — what else is WowWee

up to? They have a new line called WowWee Alive. Think wall-mounted singing fishdeveloped many times over or animal heads more lifelike than Disney animatronicsand you’ve got the idea. These mentally engaging, emotionally stimulating, realisticcreatures are intelligent, well-crafted interactors you can add to your environment.Full of complex capabilities and other surprises to make you wonder whether they’realive, these critters are sure to challenge your love of Furby. These robot busts — whichinclude a chimpanzee head, for example — can be programmed and controlled viaR/C or function fully autonomously in their free roam mode. Like Disney animatronics,these robotic conversation pieces can interact with you and each other.

The FFuture oof RRobosapien aand FFriends

WowWee, Ltd., is a Hong Kong consumer electronics and leisure productmanufacturer launched by robotics physicist Mark Tilden.

Formerly with JPL, DARPA, and NASA,Mark has introduced the bigger, morepowerful, and adaptive Robosapien2, aswell as new Roboraptor and Robopetrobots as of the 2005 CES, held in January.

Mark shared his original Robosapiencreation with the world about two yearsago. The product has since been dubbedthe most advanced human-like robot available — and he has many more robotsin the works today.

A full 14 inches tall, the firstRobosapien had 67 pre-programmed func-tions; Robosapien2 will have a surprisinglyhigher number of functions, though noteverything about this toy release — slatedfor September — is yet known.

Mark TTilden aand WWowWee


SERVO 03.2005 49

his repertoire.Fundamentals include the ability to crawl, walk, sit, stay,

and even run and jump. Robopet can lie down, beg, bark,howl, and roll over. Additional tricks and training can be programmed in.

Like a real dog, he responds to positive (and negative)feedback and reinforcement. Multiple sensors give Robopetobject recognition and avoidance techniques. He can react tosound, making him ever on the alert and fit for guard duty.This bot also follows laser drawn paths.

RoboraptorWhat’s bigger than a breadbox, smaller than

Robosaurus, and happier than Julia Roberts after giving birthto twins? It’s Roboraptor! Just look at that beautiful smile!Remember, when you can’t brush, eat something that carriesaway plaque — like a car or your sibling’s femur bone. That’swhat Roboraptor does to maintain his pearly whites.

Yes, Roboraptor may look wired on caffeine, but he’sactually wired on ... wires, from head to tail. Look at thosebig, buggy eyes — what else could keep a dinobot that jazzedother than consistent jolts from electric volts?

This R/C robotic dinosaur stretches 32 inches in length.All his talents appear to come in sets of three. For example,Roboraptor has three markedly different gaits for movement,

including walking, running, and stealthy, predatory stalking.Another member of the multi-sensing crowd, Roboraptor

can see, hear, and feel environments and people. Touch sensors on both head and tail and sonic sensors help him toaccomplish these feats.

As you might expect of any dinosaur, Roboraptorexhibits three very different moods. (Can we say Bi-polar-saur?) He can take on the personality of a hungry hunter orbe cautious or even playful.

If you caress his face when he’s in playful mode, he’llnuzzle up to you, but if you get near his jaws when he’s inhunter mode, he’ll become an aggressor. With his powerfuljaws, Roboraptor can lift objects or bite down — snap, snap, snap!

Thank You. Thank You VeryMuch.

Prior to the holiday season, the premiere Robosapienreceived 30-some honors from top industry observers andpublications. Many awards were proffered as a result of childtesting panels. The response has been the same worldwide.See “Resources” for information about these honors andawards. Imagine the response Robosapien2 and friends willgenerate during the holidays this year. SV

Robosapien2 CComes tto LLife WWith DDomestic aand PPrehistoric CCompanions

A wwink, aa ssmile, aa fflash oof tthe ccamera, aand II’m hhavingthis pphotographer ffor llunch!

If II ddidn’t kknow iit wwas RRoboraptor’s RRC, II’d sswear iit wwas aamodel ffor ssome ffunky, nnew ccatamaran. SSee tthe ttiger sstripes?

1. Check out the Robosapien2 online at ... gee, what’s that link?Oh, yeah! www.robosapienonline.com where you’ll also findreference to the numerous awards and recognitionsRoboSapien has garnered.

2. Get a gander at the new WowWee arrivals at www.wowwee.com

3. Have you Googled for “how to hack Robosapien” lately?Expect some serious Robosapien2, Robopet, and Roboraptorhacking this year!

Resources

CES 2005 was the spot where WowWee’s robotic arm lifted the veil to uncover Robosapien2, two other advanced

robots, and other spell-binding technologies.Roboraptor and Robopet join the taller, more capable

Robosapien2.WowWee is, in fact, so wowed by the response to its

offerings to date that it is expanding its robotic platform andlines to include Robonetics entertainment robots — a wholeother story in themselves.

Robosapien HHits VVegas


HouseAd.qxd 2/3/2005 1:46 PM Page 50

SERVO 03.2005 51

AAArobot’s ability to determine where it is spacially andwhere it needs to go remains one of the most important

aspects of sensing and programming. In Part I of this series,we built several user interface components, and this month,we will put those components to use as we add intelligenceto the RidgeWarrior II robot we’ve been programming. Sincewe are focusing on robotics software, we have chosen touse an off-the-shelf robot kit — the IntelliBrain™-Bot fromRidgeSoft, shown in Figure 1. We are programming in Java™

using the RoboJDE™ software development environment,which is included with the IntelliBrain-Bot kit. Java sourcecode for this series of articles is available at www.ridgesoft.com\articles\ridgewarriorii\ridgewarriorii.htm

Our next major goal is to develop components that giveour robot the ability to track its position, a process called local-ization. One common method of localization is dead reckoning,where the robot uses measurements of speed, heading, and time to deduce its position.Landmark-based localization is another common method, and although many methods of localization exist, none is perfect.

Dead reckoning is dependenton accurate speed, heading, andtime measurements, and meas-urement errors will result in anerror in the robot’s deducedposition. The error will tend toincrease over time, causing therobot’s deduced position to driftfurther and further from its realposition as it travels about. With

landmark-based localization, accumulated error is less of a concern, as the robot measures its position off of fixedlandmarks that don’t drift over time. However, the robot has to deal with difficulties in identifying landmarks and navigating through areas where it is unaware of landmarks.

Localization is a difficult problem. Choosing an effective

bbyy SStteevvee GGrraauu

Figure 22. Navigation and Localization class diagram.

FFiigguurree 1

Figure 3. Hybrid Localizer class diagram.

Grau2.qxd 1/28/2005 3:52 PM Page 51

method will depend on the requirements for a particularrobot, while combining several methods may be effective.For example, a robot might use dead reckoning to navigateto the vicinity of a landmark then switch to landmark-basednavigation, just as a ship’s captain might use dead reckoningwhile out of sight of land and then switch to landmark-basednavigation when land is in sight.

What tto DDo?So, what method of localization should we use for our

robot? Rather than attempting to pick an ideal localizationmethod, we can instead choose to design our software to

support a variety of localization methods. By designing ageneric interface to any “localizer” component (Java class), we can allow various localization methods to be used interchangeably and also allow multiple methods to be combined into hybrid methods. The localization function canbe implemented as a cohesive component that is loosely coupled to other software components that make up ourrobot’s control program.

The LLocalizer IInterfaceWe will define a generic Java interface named

“Localizer,” which allows different localization methods to beused interchangeably. Figure 2 shows a class diagram depictingnavigation and localization classes. In order to navigate therobot from place to place, the Navigator relies on theLocalizer to provide the robot’s current position and heading:its “Pose.” Figure 3 illustrates how multiple localizers could beused to form a hybrid localizer that tracks the robot’s positionusing a combination of localization methods.

Our generic Localizer interface will need to declare amethod to retrieve the current Pose (position and heading).We will also declare methods to set these values so therobot’s initial position can be set and so the position can becorrected from time to time. We will define this interface inJava as follows:

public interface Localizer {public Pose getPose();public void setPose(Pose pose);public void setPosition(float x, float y);public void setHeading(float theta);

}

Our Pose object will need member variables to keep trackof the position in x and y coordinates — we won’t worry aboutelevation changes — and the direction the robot is heading,which we will call theta. Since the Pose class is very simple,we will make the member variables directly accessible to otherclasses by declaring them “public.” This will allow fasteraccess to these variables than if they had to be read throughget methods such as pose.getX() and pose.getY(), savingcomputing power for other tasks. We also want to prevent aPose object from changing while it is being used for naviga-tion calculations. Therefore, we will make it immutable bydeclaring its member variables “final.” Final member variablescan’t be changed after an object has been constructed.

public class Pose {public final float x;public final float y;public final float theta;

public Pose(float x, float y, float theta) {this.x = x;this.y = y;this.theta = theta;

}}

The Localizer interface is not specific to one localizationtechnology or another. This allows other software components

52 SERVO 03.2005

Creating RReusable RRobotic SSoftware CComponents

Figure 44. Nubotics WheelWatcher WW-01 sensor.

Figure 55. Analog wheel encoder.

Grau2.qxd 1/28/2005 3:54 PM Page 52

to work interchangeably with a variety of localizationmethods. We’ve defined theLocalizer interface such that itprovides a cohesive function— tracking the robot’s posi-tion and loose coupling toother software components— promoting reusability andinterchangeability of classeswe develop to the Localizerinterface.

Implementinga LLocalizer

We are now ready to putthe Localizer interface towork. The IntelliBrain-Bot kitwe are using includes twoinfrared photoreflector sen-sors that can be used to create encoders that senserotation of the robot’swheels. Our robot can usethese sensors to measure its motion, allowing it to keep trackof its position using dead reckoning. For greater accuracy, wecan use WheelWatcher™ WW-01 sensors from Nubotics,shown in Figure 4. Working with two different encoder sensors will allow us to further experiment with buildingreusable and interchangeable software components.Therefore, we will go ahead and program our robot to workwith either type of wheel encoding sensor.

Analog EEncodersThe IntelliBrain-Bot comes with wheels that have eight

spokes, as shown in Figure 1. The spokes are separated byeight oblong holes in the wheels. We can detect wheel rotation by mounting the Fairchild QRB1134 sensors thatcome with the IntelliBrain-Bot such that the spokes and holesin the wheels pass in front of the sensors as the wheels turn.

Each QRB1134 sensor consists of an infrared emitter anddetector pair. When the sensor is close to a solid surface, thedetector will sense infrared light from the emitter reflectingoff of the surface. When there is no surface to provide areflection, the detector will not sense the light output fromthe emitter. By mounting a sensor near each wheel in such away that the holes and spokes in the wheel pass in front ofthe sensor (as described in the IntelliBrain-Bot AssemblyGuide), our software will be able to use the signal from thedetector to sense wheel rotation.

Let’s first implement a small test function to sample onesensor’s detector signal. This will enable us to create a graphshowing the behavior of the sensor’s output as the associatedwheel rotates. We will create a class named TestEncoder andadd it to the list of selectable functions we created in the

previous article. All this function will do is power the servo,wait briefly to allow the wheel to reach full speed, then samplethe detector output every five milliseconds for half a second,storing the sampled data in an array. Once the data has beencollected, the function will wait until the START button ispressed, then print the data to the debug output streamSystem.out. We can then copy the data from the RoboJDE“Run” window and paste it into a spread sheet program tograph the data. The following Java code implements this:

public void run() {mServo.setPosition(100);try {

Thread.sleep(500);} catch (InterruptedException e) {}int[] samples = new int[100];long nextTime = System.currentTimeMillis();for(int i = 0; i < samples.length; ++i) {

samples[i] = mEncoderInput.sample();nextTime += 5;try {

Thread.sleep(nextTime -System.currentTimeMillis());

} catch (InterruptedException e) {}}mServo.setPosition(50);while (!mButton.isPressed());for (int i = 0; i < samples.length; ++i) {

System.out.println(Integer.toString(i * 5) + ‘\t’ + samples[i]);}

}

The chart in Figure 6 shows the results from this test. Thesampled value is low when a spoke is in front of the sensorand high when a hole is in front of the sensor. The rising and

PART 2

Figure 66. Analog encoder data.

SERVO 03.2005 53

Grau2.qxd 1/28/2005 3:55 PM Page 53

falling edges correspond to the edges of the spokes. The rising-edge-to-rising-edge time is roughly 150 millisecondswhen the wheel is spinning at full speed. Since the wheel haseight spokes, we can calculate that it takes about 1.2 seconds(8 x 150) for the wheel to turn one revolution. The top speedof the wheel is approximately 50 revolutions per minute. Oursoftware will need to sample more frequently than at leastevery 75 milliseconds to ensure it sees each spoke go by. Ifwe sample at a high enough frequency to count the passingof both edges of each spoke, we can measure the wheelposition to an accuracy of 1/16 of a revolution.

Creating aan AAnalogShaftEncoder With Java’s multi-threading capability, it will be easy to set

up a thread to sample each wheel encoder sensor periodically.All we need to do is create a new class — AnalogShaftEncoder— which is a subclass of Java’s thread class. Each instance ofthe class will be a separate thread that monitors the rotation ofa single wheel. Our RidgeWarriorII class will create twoinstances of this class: one for each wheel.

The run method of the AnalogShaftEncoder will loop forever, checking if the edge of a spoke has passed by thesensor since the previous check. After each check, the threadwill need to sleep to allow other threads to execute. Thelonger the thread sleeps, the less CPU time it will consume;

if it sleeps too long, however, it will miss spoke edges. It willalso be a good idea to enclose all of the code in the runmethod in a try-catch block to catch and report any errors thatoccur. We don’t expect there to be any errors, but if there isa problem with our code, it will be much easier to debug if itprints out a stack trace rather than just allowing the thread toterminate silently. The following code lays out this structure:

public void run() {try {

// take initial sensor sample:

while (true) {// sample the sensor and count// spoke edges

:Thread.sleep(mPeriod);

}}catch (Throwable t) {

t.printStackTrace();}

}

In order to count spoke edges, the run method will needto keep track of whether the sensor signal was high or lowon the previous check, then adjust the spoke edge counter ifthe sensor switched to the opposite state. We can implementthis easily by using a Boolean variable to keep track ofwhether the previous reading was high or low. The followingcode uses the “wasHigh” variable to do this:

int value = mInput.sample();if (wasHigh) {

if (value < mLowThreshold) {// update count

:wasHigh = false;

}}else {

if (value > mHighThreshold) {// update count

:wasHigh = true;

}}

The low and high thresholds are the software equivalentof a Schmitt trigger in an electronic circuit. This thresholdchecking makes the state of the wasHigh variable sticky —that is, it adds hysteresis. Thus, the state will only changewith large swings in the sampled value and our encoder willbe less susceptible to noise causing false counting.

Finally, our AnalogShaftEncoder will need to be told thedirection power is being applied to the wheel and to knowwhether to increment or decrement the encoder count eachtime an edge is detected. To do this, we will create aDirectionListener interface:

public interface DirectionListener {public void updateDirection(boolean isForward);

}


54 Circle #94 on the Reader Service Card.

Grau2.qxd 1/28/2005 3:56 PM Page 54

The code controlling the motor will then be able to tell theencoder which direction the motor is applying power. Theencoder will set the state of a member variable — mIsForward— each time it receives an updateDirection call. The encoder willuse the direction information when updating the edge count todetermine if the count should be incremented (wheel is rotatingforward) or decremented (wheel is rotating backward):

if (mIsForward)mCounts++;

elsemCounts--;

We will also need to implement the getCounts methodto give other classes access to the encoder’s counter:

public int getCounts() {return mCounts;

}

WheelWatcher EEncodersThe analog shaft encoders we have just created acknowl-

edge 16 counts for each revolution of the wheel. Assumingthere are no other errors, the robot can measure its positionto 1/16 of the wheel circumference, which is approximately1/2 inch. This accuracy is fine for forward motion, but it only allows the robot to measure its heading to a precision of13 degrees. With this level of precision, our dead reckoninglocalizer will not be highly accurate.

The WheelWatcher WW-01 from Nubotics is a quadratureshaft encoder designed for hobby servos. These sensorsmount nicely on the IntelliBrain-Bot and accrue 128 countsper wheel revolution. The quadrature technique they usealso allows the sensor to sense the direction of the wheel.We will need to replace the wheels, however, because theadhesive code wheel can’t be attached to the stockIntelliBrain-Bot wheels. Using this sensor will improve theprecision of heading measurements to within two degrees.Of course, this is assuming there are no other sources oferror. Wheel slippage and other sources of error will reducethe accuracy.

The IntelliBrain robotics controller has built-in supportfor quadrature shaft encoders, so we will not have to createany additional classes to use these sensors. Instead, we can simply use the IntelliBrain.getShaftEncoder method to get aquadrature encoder object and then initialize it with the twoIntelliBrain digital input ports the WheelWatcher sensor uses,as follows:

leftEncoder = IntelliBrain.getShaftEncoder(1);

((IntelliBrainShaftEncoder)leftEncoder).initialize(IntelliBrain.getDigitalIO(1),IntelliBrain.getDigitalIO(2));

Tracking UUsing DDead RReckoningWith the ability to measure the rotation of each wheel,

we can create a class that will keep an estimate of the robot’sPose. If the robot moves straight ahead, the distance it travelsis simply the average number of encoder counts the twowheels turn times the distance the robot travels per encodercount. This can be calculated by the following equations:

distancePerCount = Pi * diameterWheel /countsPerRevolution;

deltaDistance = (leftCounts + rightCounts) / 2 *distancePerCount;

If the robot rotates in place by turning its wheels inopposite directions, the wheels will trace a circle whose diam-eter is equal to the track width of the robot. The robot’sheading changes as the wheels make their way around thiscircle. The robot will rotate 2π radians (360 degrees) whenthe wheels have traversed the circumference of this circle.The number of encoder counts to rotate a full circle dependson the geometry of the robot and can be calculated by:

countsPerRotation = (trackWidth / wheelDiameter) *countsPerRevolution;

This is the number of counts for a single wheel. If wetake the difference in counts between the two wheels andnote that each rotation is 2π radians, we can rearrange thisequation into the following two equations:

radiansPerCount = Pi * (wheelDiameter/trackWidth) /countsPerRevolution;

SERVO 03.2005 55

PART 2

Figure 7. Circle traced by robot turning in place.

Grau2.qxd 1/28/2005 3:57 PM Page 55

deltaTheta = (rightCounts – leftCounts) *radiansPerCount;

where deltaTheta is the angle in radians the robot rotates.Given the left and right encoder counts, these equations

enable our program to estimate the robot’s position — provided it moves straight ahead or rotates in place — butwhat if the robot moves along an arbitrary path?

Our localizer class can estimate the robot’s positionalong an arbitrary path by treating the robot’s motion asmany small, discrete movements. By summing all of the discrete movements the robot makes, the localizer can estimate the robot’s current position.

As shown in Figure 8, the robot moves a small distance,∆d (deltaDistance), while it travels forward in the directionΘ (theta). Assuming the direction the robot is heading doesn’t change significantly during each step, the change inthe position along the x axis, ∆x (deltaX), and change in position along the y axis, ∆y (deltaY), can be calculated usingthe following trigonometric calculations:

float deltaX = deltaDistance * (float)Math.cos(mTheta);

float deltaY = deltaDistance * (float)Math.sin(mTheta);

The ∆x and ∆y values can then be added to the previous position estimate to obtain a new position estimate. As withseveral other classes we have created, the Odometric-Localizer class will extend the Thread class and do its main

work in a timed loop in its run method, as follows:

long nextTime = System.currentTimeMillis();while(true) {

// read encoders:

// calculate change in pose:

// update position and heading estimates:

nextTime += mPeriod;Thread.sleep(nextTime -

System.currentTimeMillis());}

Reading the encoders is simply a matter ofcalling each encoder’s getCounts method:

int leftCounts = mLeftEncoder.getCounts();int rightCounts = mRightEncoder.getCounts();

Conveniently, this code does not depend on the specifictype of shaft encoder sensor the robot uses. TheShaftEncoder interface has enabled loose coupling betweenthe encoder classes and our localizer class, facilitating interchangeability. Hence, the localizer can workwith any encoder that supports the ShaftEncoder interface.

Updating the position and heading estimates is just amatter of adding the ∆x, ∆y, and ∆Θ values into the previousposition estimate. However, because there are multiplethreads accessing the Pose data, we have to be careful toensure that another thread doesn’t read the Pose data whilethe localizer thread is updating it. We can use Java’s built-insynchronization mechanism to coordinate access to theshared data by putting the update code in a synchronizedcode block and adding the “synchronized” modifier to allmethods that allow other threads to access the Pose data.The following code will update the position:

synchronized(this) {mX += deltaX;mY += deltaY;mTheta += deltaTheta;

// limit theta to -Pi <= theta < Piif (mTheta > PI)

mTheta -= TWO_PI;else if (mTheta <= -PI)

mTheta += TWO_PI;}

Finally, we will need a getPose method to allow otherthreads to read the Pose data.

public synchronized Pose getPose() {return new Pose(mX, mY, mTheta);

}

TestingIn order to test the AnalogShaftEncoder and Odometric-


56 SERVO 03.2005

Figure 88. Calculating discrete position changes.

RidgeWarrior II Source codewww.ridgesoft.com\articles\ridgewarriorii\ridgewarriorii.htm

IntelliBrain-Bot Kitwww.ridgesoft.com\intellibrainbot\intellibrainbot.htm

WheelWatcher WW-01 Quadrature Encoderswww.nubotics.com

RREESSOOUURRCCEESS

Grau2.qxd 1/28/2005 3:57 PM Page 56

Localizer classes we’ve now constructed, we will need toconstruct left and right encoder object instances and con-struct a localizer object instance in the RidgeWarriorII mainmethod, as well as implement a few test classes. TheOdometricLocalizer class requires the wheel diameter andtrack width measurements of the robot to be provided in itsconstruction. For the IntelliBrain-Bot, these are approximate-ly 2.65 inches and 4.55 inches, respectively.

We will need two new screens: one to view theencoder counter values and the other to view the Pose datafrom the localizer. We will also need a few test functions tomove the robot in different ways so we can verify theencoders and localizer function correctly. Source code forfive test classes — EncoderCountsScreen, PoseScreen,TimedForward, TimedRotate, and TimedSquare — is available online. The latter three classes power the servosfor fixed periods of time to cause the robot to move in aspecific pattern, as indicated by the name of each class. Byrunning these tests and observing the data displayed onthe LCD screen, we can validate the functionality of ourencoder and localizer classes.

ConclusionIn this article, we’ve added two more reusable classes

that support shaft encoding and localization. We have used

Java’s multi-threading and interface features to designthese classes such that they are loosely coupled to othercomponents that make up our robot’s control program.This facilitates reuse of these classes in other robot software projects. It also allows us to replace the classeswith other classes that provide the same function but in adifferent way. We demonstrated this by allowing our analog shaft encoders to be used interchangeably with theWheelWatcher quadrature shaft encoders. In the future,we could make use of other localization techniques — forexample, landmark recognition — by replacing theOdometricLocalizer with another class that uses a differentlocalization method. The Localizer interface allows thelocalizer function to be a cohesive component with plug-and-play interchangeability.

In our next article in this series, we will implement classesthat use the output of our localizer to navigate the robotfrom place to place. SV

PART 2

SERVO 03.2005 57

Steve Grau has been developing software for over 20 years. He is the founder of RidgeSoft, LLC, and the author of the RoboJDE, a Java-enabled robotics software developmentenvironment.

AABBOOUUTT TTHHEE AAUUTTHHOORR


Grau2.qxd 1/28/2005 3:58 PM Page 57

We accept VISA, MC, AMEX, and DISCOVERPrices do not include shipping and

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The SERVO BookstoreMind Candy

For Today’s

Roboticist

Mobile Robotic Car Designby Pushkin Kachroo / Patricia

Mellodge This thoughtful guidegives you complete,illustrated plans andinstructions for buildinga 1:10 scale car robotthat would cost thousands of dollars ifbought off-the-shelf. But, beyond hours ofentertainment and satisfaction spent creating and operating animpressive and fun project, Mobile RoboticCar Design provides serious insight into thescience and art of robotics. Written byrobotics experts, this book gives you a solidbackground in electrical and mechanical theory, and the design savvy to conceptualize, enlarge, and build roboticsprojects of your own. $29.95

Electronics Demystifiedby Stan Gibilisco

Now anyone with aninterest in electronicscan master it by readingthis book. In ElectronicsDemystified, best-sellingscience and math writerStan Gibilisco providesan effective and pain-less way to understandthe electronics thatpower so much of modern life. WithElectronics Demystified, you master the sub-ject one simple step at a time — at your ownspeed. This unique self-teaching guide offersproblems at the end of each chapter, a section to pinpoint weaknesses, and a 70-question final exam to reinforce the entirebook. If you want to build or refresh yourunderstanding of electronics, here’s a fastand entertaining self-teaching course that’scompletely current. $19.95

Electronic Gadgets for theEvil Genius

by Robert Iannini The do-it-yourself hobbyist market — particularly in the areaof electronics — is hotter than ever. Thisbook gives the “evilgenius” loads of projects to delve into,from an ultrasonicmicrophone to a bodyheat detector, all the way to a Star WarsLight Saber. This book makes creating thesedevices fun, inexpensive, and easy. $24.95

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58 SERVO 03.2005

ROBOT DNA SERIESThree Volume Pack

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All the data you need to build your ownrobot base:• Mechanical Construction• Electrical Construction• Operating Power• Robot Designs• Constructing a Two-Wheeled Rover Robot• Selecting the Right Materials• Glossary of Terms• Tables, Formulas, and Constants

Subscribers: $21.95 each bookNon-subscribers: $24.95 each book

Robot Programmingby Joe Jones / Daniel Roth

Using an intuitive method,Robot Programmingdeconstructs robot control into simple anddistinct behaviors that areeasy to program anddebug for inexpensivemicrocontrollers with littlememory. Once you’vemastered programming your online bot, youcan easily adapt your programs for use inphysical robots. $29.95

Build Your Own All-TerrainRobot

by Brad Graham / Kathy McGowan Remotely operatedrobots are becomingincreasingly popularbecause they allow theoperators to exploreareas that may not normally be easilyaccessible. The use ofvideo-controlled technology has sparkeda growing public interest not only in hobbyists, but also in the areas of research,space, archeology, deep sea exploration,and even the military. Inside Build Your OwnAll-Terrain Robot, the writers enable eventotal newcomers to robots to construct arugged, video-controlled, talking, seeing,interacting explorer bot with a range of overa mile for under $200.00! $29.95

Robot Builder's Bonanzaby Gordon McComb

Robot Builder’s Bonanzais a major revision of thebestselling bible of amateur robot building —packed with the latest inservo motor technology,microcontrolled robots,remote control, LEGOMindstorms Kits, andother commercial kits. It gives electronicshobbyists fully illustrated plans for 11 complete robots, as well as all-new coverageof Robotix-based robots, LEGO Technic-based robots, Functionoids with LEGOMindstorms, and location and motorizedsystems with servo motors. $24.95

Robot Building for Dummiesby Roger Arrick / Nancy Stevenson

Ready to enter the robotworld? This book is yourpassport! It walks youthrough building yourvery own little metalassistant from a kit, dress-ing it up, giving it a brain,programming it to dothings, even making ittalk. Along the way, you’llgather some tidbits about robot history,enthusiasts’ groups, and more. $21.99

BookstoreMar05.qxd 2/3/2005 10:04 AM Page 58

Check out our online bookstore at www.servomagazine.com for a complete listing of all the books that are available.

SERVO 03.2005 59

To order call 1-800-783-4624 or go to our website at www.servomagazine.com

PIC Microcontroller Project Bookby John Iovine

The PIC microcontrolleris enormously popularboth in the US andabroad. The first editionof this book was atremendous successbecause of that.However, in the fouryears that have passedsince the book was firstpublished, the electronics hobbyist markethas become more sophisticated. Many users of the PIC are now comfortable payingthe $250.00 price for the Professional version of the PIC Basic (the regular versionsells for $100.00). This new edition is fullyupdated and revised to include detaileddirections on using both versions of themicrocontroller, with no-nonsense recommendations on which one serves better in different situations.$29.95

Build Your Own HumanoidRobots

by Karl Williams Build Your OwnHumanoid Robotsprovides step-by-stepdirections for six excitingprojects — each costingless than $300.00.Together, they form theessential ingredients formaking your ownhumanoid robot. $24.95

Robotics Demystifiedby Edwin Wise

There's no easier, faster,or more practical way tolearn the really toughsubjects. McGraw-Hill'sDemystified titles are the most efficient, intriguingly written brush-ups you can find.Organized as self-teaching guides, theycome complete with key points, backgroundinformation, questions for each chapter, andeven final exams. You'll be able to learn morein less time, evaluate your strengths andweaknesses, and reinforce your knowledgeand confidence. $19.95

CNC Roboticsby Geoff Williams

Now, for the first time,you can get completedirections for building aCNC workshop bot for atotal cost of around$1,500.00. CNC Roboticsgives you step-by-step,illustrated directions fordesigning, constructing, and testing a fullyfunctional CNC robot that saves you 80 percentof the price of an off-the-shelf bot and canbe customized to suit your purposes exactly,because you designed it. $34.95

JunkBots, Bugbots, and Bots onWheels: Building Simple Robots

With BEAM Technologyby Dave Hrynkiw / Mark W. Tilden

From the publishers ofBattleBots: The OfficialGuide comes this do-it-yourself guide to BEAM(Biology, Electronics,Aesthetics, Mechanics)robots. They're cheap,simple, and can be builtby beginners in just a fewhours, with help from this expert guide complete with full-color photos. Get readyfor some dumpster-diving! $24.99

LINUX Robotics: ProgrammingSmarter Robotsby D. Jay Newman

Robotics is becoming anincreasingly popular fieldfor hobbyists and profes-sionals alike. The cost ofthe mechanics and electronics required tobuild a robot are lowenough that almost anyone can afford it. Thehardware that used to require governmentfunding or a large university grant is now available to the average person. At thesame time, programming is becoming a common skill. This book combines the most sophisticated parts of robotics andprogramming to fill a real gap in availableinformation. Most robotics books today usemicrocontrollers as the “brains” of therobots. This approach is fine for smaller, less expensive projects, but has serious limitations. When attempting to build a robot with sophisticated movements, navigation, vision, and picture-capturing abilities, it is better to use Linux as the controller. This book is available for sale February 15, 2005. $34.95

Robot Builder's Sourcebookby Gordon McComb

Fascinated by the world of robotics, but don’tknow how to tap into theincredible amount of information available onthe subject? Clueless as tolocating specific information on robotics?Want the names, addresses,phone numbers, and websites of companiesthat can supply the exact part, plan, kit,building material, programming language,operating system, computer system, or publication you’ve been searching for? Turnto the Robot Builder’s Sourcebook — aunique clearinghouse of information that willopen 2,500+ new doors and spark almost asmany new ideas. $24.95

Robot Mechanisms andMechanical Devices Illustrated

by Paul SandinBoth hobbyists and professionals will treasurethis unique and distinctivesourcebook — the mostthorough — and thoroughlyexplained — compendiumof robot mechanisms anddevices ever assembled.Written and illustratedspecifically for people fascinated with mobile robots, Robot Mechanisms andMechanical Devices Illustrated offers a one-stop source of everything needed for themechanical design of state-of-the-art mobile‘bots. $39.95

Build Your Own ElectronicsWorkshop

by Thomas Petruzzellis The ElectronicsWorkshop was writtento assist the newcomerto the field of practicalelectronics through thecreation of a personalelectronics workbench.This is a place speciallydesigned so that read-ers can go there towork on an electronic project, such as test-ing components, troubleshooting a device,or building a new project. This bookincludes invaluable information, such aswhether to buy or build test equipment,how to solder, how to make circuit boards,how to begin to troubleshoot, how to testcomponents and systems, and how to buildyour own test equipment, complete withappendix and resources, etc. This is THEbook for anyone entering the field or hobbyof electronics. $29.95

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BookstoreMar05.qxd 2/3/2005 10:06 AM Page 59

60 SERVO 03.2005

[email protected] David Geer

Finland’s Plustech Oy Timberjack Walking Forester

These Walking ForestMachines can cut

and fell trees about20 inches thick.

What has six legs, weighs more than 10 tons, and walks through the forestwith a grace near that of a gazelle? It’s not a dancing machine, but it is aWalking Forest Machine. Its computer intellect controls walker direction,

speed, step height, walking gait, and ground clearance.

Geerhead.qxd 2/2/2005 12:48 PM Page 60

Finnish Forest ForagerFinland is noted for its contribution

to cell phone media with the house-hold name of Nokia, but Finland isn’tonly just “a phone call away.” It’s also“a walk in the park!”

A division of John Deere (and asubsidiary of Timberjack, the world'sleading designer, manufacturer, anddistributor of forestry equipment),Plustech Oy makes the TimberjackWalking Forest Machine, an industrialstrength, working robot that walks upmountains and through forests to cut,fell, and carry off monstrous trees inminutes. The same giants of the wood-lands that once took two men withstrong arms, heavy axe heads, and a lotof perspiration to tackle are now razedas easy as a florist clips a long-stemmedrose.

These Walking Forest Machinescan cut and fell trees about 20 inchesthick. These are all signs that say manya future lumberjack will be a heavyequipment operator sitting in thesweet seat of a machine just like this one.

Actually, non-walkers fromTimberjack — the track and wheel

variety — have been doing the lumber-jack’s work for years, so why have theydecided to develop a walker all of asudden instead of these other meansof mobility? It seems that the wheeledand tank-like tracked vehicles tend todamage sensitive forest soils. Walkersare much less of a problem for the environment.

Six-Legged TreeSpiders

The Walking Forest Machines

come in weights of 11 and 15 metrictons, and they can lift trees of about1.5 metric tons each, depending on thereach of the particular prototype’sboom. These Foresters are also agile,walking up 30-degree slopes withoutlosing their balance, and since they run on diesel fuel, they can work a double shift — a full 16 hours —without refueling.

Though the Walking Foresters doless harm to the soil than tracks orwheels, they do face some of the samedevelopmental challenges as other

SERVO 03.2005 61

GEERHEAD

They can lift trees of about 1.5 metric tons each, dependingon the reach of the particular prototype’s boom.

Mobility is placed in the hands, or hand, of the operatorvia a single, intuitive, user-friendly joystick.

Plustech (a division of JohnDeere) makes the Timberjack WalkingForest Machine, which traversesforests with ease via six legs and feetto harvest trees while protecting theground from the damage wheeledand tracked vehicles would other-wise do.

The machine acclimates itself to the terrain automatically byresponding to input from sensors.The machine can redistribute its

weight to balance itself over varyinglandscapes. It finds solid footing for each of its legs. Ground pressurecan be adjusted because of itschangeable shoes.

Because of the walker’s advancedcontrol system, the operator onlyneeds to move a single joystick toselect direction and speed. Theautomated computer system does allother thinking and respondingwhere movement is concerned.

DOING THE TIMBERJACK STRUT!


types. Speed, cost, and reliability are allconcerns of Plustech’s R&D.

“It’s Got Legs!”The Walking Forester’s legs are

more than just three pairs of oversizedstocking stuffers. Each of its six agile,ambulatory appendages is about ninefeet wide and 30 feet long. These are

all directed by one joystick, which alsocontrols the Walking Forester’sground clearance, frame tilt, and rollangles.

The Forest Walker can step ahead,back, side-to-side, and diagonally. It can step over obstacles, turn in place, and adjust to the terrain by altering ground clearance and theheight of each step with the assistance

of its operator.

Backbone and BrainsFrom the legs to the nerves, from

the nerves to the brain ... the Forester’snervous center is a computer systemwith a high IQ. Its computer intellectcontrols the Forester’s direction, speed,step height, walking gait, and ground

62 SERVO 03.2005

GEERHEAD

The Walking Foresters can step over obstacles instead ofattempting to drive through them.

The Walking Forester’s ability to turn in place makes it highlydesirable for confined spaces.

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clearance.The Walking Forester’s tree

harvesting head is controlled by theTimberjack measuring and control system, while the loader and engineare controlled by yet another systemcalled the Total Machine Control system.

Mobility is placed in the hands, orhand, of the operator via a single, intuitive, user-friendly joystick.

Forests of the FutureAdvocates of forest soil preserva-

tion have demanded a solution to theravaging of modern forestry for sometime. In 1995, Plustech Oy responded

with the Walking Forest Machine.Though still not in production, theWalking Forester has been developed and tested in several ofthe world’s forests to adapt it to avariety of working conditions andenvironments.

The testing will continue until Plustech is certain themachine will hold up long-term in the demanding working environments of the world’sforests. Plustech wants to develop Walking Foresters forevery type of foresting conditionand requirement.

The current WalkingForesters prototypes have already

required a great deal of research and testing in new automation

Like non-perambulating Timberjackharvesters, the Walking Forest Machineprototype is outfitted with a Timberjack3000 measuring and control system andharvester head.

Via this system, an operator can setparameters for timber harvesting basedon the priorities of the forest owner. Anoperator can also monitor productionbased on tree species and volume oftrees taken.

USING TREES FOR CHEW TOYS!

SERVO 03.2005 63

GEERHEAD

One of the most popular questions is how you sustain a project that requires so muchspending on the development of an unconventional, experimental technology over such a long period?

The wheeled versions of theTimberjack forest machines havebeen available since 1947. Productsinclude a wide range of machinesfor harvesting, terrain transport,and log loading.

Because Timberjack machinesare on the job in over 80 countries,the brand has a solid foundationfrom which to grow into the future.They have determined that this isthe direction in which to move, andif they intend to stay in this business,they must make this kind of aninvestment.

Timberjack has, in fact, invested in product developmentthrough two primary research and

development centers in Canada andFinland. The Walking Forest Machineproject is the fruit of Plustech, aTimberjack affiliate that specializesin long-term R&D.

Plustech is only a portion ofTimberjack’s massive European R&DCenter in Tampere, Finland. The current overarching goal of themachine is to examine just howappropriate walking technology isfor harvesting forests.

HOW CAN THEY AFFORD TO INVEST SO MUCH IN DEVELOPMENT?


technologies and mobile hydraulics.They also need to meet these requirements while keeping down theultimate price tag.

In time, we shouldexpect to see them or theirvariants hard at work clear-ing forests and preservingforest floors through theirwalking technology.

Adapt to theEnvirons

R&D has so far demon-strated that walking tech-nology is highly suitable tosteep slopes and softground types where otherharvesting machines andmethods prove to causeirreparable damage to theforest, specifically in theform of ground erosion.

The Walking Foresterscan step over obstacles

instead of attempting to drive throughthem. It can optimize the distributionof ground pressure in order to steplightly — so-to-speak — as well as

minimize disturbance of soil and tree roots.

The Walking Forester’s ability toturn in place makes it highly desirablefor confined spaces, and whateverthe legs are doing, the carrier canmaintain an even keel so theForester’s operator can maintain anacceptable level of comfort.

The Walking Foresters areextremely stable and precise for accurate crane movement and usage.

Author, Author!Encore, Encore!

The Timberjack Walking ForestMachine has been honored with several awards, including the 1997European IT Prize. In selecting therecipient of this award for design andinnovation, 25 finalists were pulledfrom a pool of 319 entrants from 27 countries.

In 1996, the Walker was highlycommended in the eco-design category of the Better EnvironmentAwards for Industry. This event recognizes those innovations thatfavorably impact the environment ascompared to other technologies.

Has It Sprung a Leak?During a press event and live

demonstration in Finland, a radio commentator was caught off guard byone of the Walking Forester’s lessreported behaviors. As is prone to happen when the Walker has just beencleaned, when it swung and tilted itsbody some remaining water spilled outof the frame.

It looked as if the Walker had justtaken, err, uh, sprung a leak! The commentator responded, ”A-a-a-andnow some kind of liquid is coming outof the machine’s body!”

Let’s See One Up ClosePlustech provides live

demonstrations of theWalking Forest Machinesat local fairs in Finland.Though they’ve tossedaround the idea of holdingdemonstrations in the US,no decision has beenmade as yet to followthrough.

Someday, I’m sure —especially once they comeinto commercial use — youcan expect Plustech and/orJohn Deere to bring overthese Walking Foresters toshow them off. SV

GEERHEAD

64 SERVO 03.2005

The walking forest machine comesin three prototypes (one basic platform and two forest harvesters).These are introduced on the Internetat www.plustech.fi/Walking1.html

Check out other Timberjackforesters and equipment at www.timberjack.com

RESOURCES

The machine can redistribute its weight to balanceitself over varying landscapes.

Though highly mobile, the Walker’s speed, cost,and reliability are concerns for Plustech’s R&D.

From inside the cockpit, the operator can con-trol ground clearance, frame tilt, and roll angles.


Robots to Fix Hubble for$154 Million

Since 1993, the Hubble SpaceTelescope (HST) has been periodicallyserviced by astronauts aboard a SpaceShuttle, replacing aging hardware andinstalling more advanced scientificinstruments. As fallout from theColumbia tragedy in 2003, the nextservice mission was cancelled last year,in part over concerns about astronautsafety. The obvious solution is a fullyrobotic service mission, and it wasrecently announced that BritishColumbia-based MacDonald, Dettwilerand Associates, Ltd. (MDA,www.mdrobotics.ca), has secured a$154 million contract from theNational Aeronautics and SpaceAdministration (NASA, www.nasa.gov) to provide exactly that. The

Hubble mission will follow two US military satellite missions that will utilizeMDA-devised solutions to perform similar tasks involving a classifiedobservation program and a satelliteservice mission. The $154 million maysound a bit pricey for a repair job, butmaybe we can try to pay them inCanadian dollars.

Nominate a Robot

In case you missed it, the RobotHall of Fame, created by Carnegie-Mellon University in 2003 to honorboth real and fictional robots thathave affected our lives, inducted five new members last year. These are Honda's humanoid ASIMO,Shakey — the autonomous robot fromSRI International, the animated character Astro Boy, Robby the Robot— a movie prop turned merchandisinggold mine, and Star Wars' C-3PO. If you want to nominate your favoriteautomaton for 2005 or vote for

an existing nominee, stop by www.robothalloffame.org

ScanEagle Goes Wireless

In case you aren't familiar with it,ScanEagle is a long endurance,autonomous unmanned aerial vehicle(UAV) developed by Boeing (www.boeing.com) and The Insitu Group(www.insitugroup.net) for militaryand homeland security applications.As of late 2004, it had logged morethan 1,400 hours of service in Iraq.ScanEagle is four feet in length andhas a 10-foot wingspan, and the current model can remain on dutyfor a shift of more than 15 hours(with a version that offers 30 hours of endurance in the works). Asa standard payload, it carries an electro-optical or infrared cameraand it can track both stationary andmoving targets from greater than16,000 feet.

The latest news is that ScanEaglehas been upgraded to perform highspeed wireless communications relayfunctions. Enabled by HarrisCorporation's National SecurityAgency approved Type 1 classifiedSecNet-11® Plus technology in theUAV's avionics bay, streaming videoand voice-over IP communications

Artist’s depiction of Hubble Telescopeand repair vehicle.

Photo courtesy of MDA.

The ScanEagle UAV now facilitatessecure wireless communications.Photo courtesy of Insitu Corp.

Honda’s ASIMO robot is a recentinductee into the Robot Hall of

Fame. Photo courtesy of Honda Motor Co., Ltd.

bbyy JJeeffff EEcckkeerrttRRoobbyytteess

Are you just an avid Internetsurfer who came across some-

thing cool that we all need to see?Are you on an interesting R&Dgroup and want to share whatyou’re developing? Then send mean email! To submit related pressreleases and news items, pleasevisit www.jkeckert.com

— Jeff Eckert

SERVO 03.2005 65

Robytes.qxd 2/2/2005 1:15 PM Page 65

were sent from a ground control station over a secure high bandwidthnetwork to ScanEagle 18 miles away.The data was then instantaneouslyrelayed to ground personnel six milesfrom the UAV.

In practical terms, this means thatit can be used by troops on the groundto receive situational data on the battlefield, securely and without delay.The company also produces theSeascan UAV, which is designed foraerial reconnaissance at sea for fishfinding, search and rescue operations,coastal patrol, and other purposes.Photos, videos, and detailed specs areavailable at the Insitu website.

Big Bot Prevents Landslides

Gravity is a pretty useful thingoverall, but, as California readers can attest, it has an ugly habit ofpulling heaps of earth from highplaces to lower places, much to thedetriment of real estate values inboth locations.

However, landslides are becom-ing more and more preventable,thanks to Roboclimber — a large scalerobot that was developed by ICOP,

which is an Italian civil engineeringcompany.

Weighing in at about 3,800 kg(10,000 lbs) and with a base of 2 x 2.5 meters (6.6 x 8.2 feet), it qualifies as one of the world's largest.Using remote technology originallydeveloped by the European SpaceAgency (ESA, www.esa.int),Roboclimber recently was put to thetest in a successful effort to reinforce anearly vertical rock wall rising from thevalley of Alta Val Torre in the Friuli-Venezia Giulia region of Italy. Thenation is plagued by more than 400landslides every year.

Basically, the robot employs anonboard Web camera to allow it to bemaneuvered into the proper positionfrom a safe distance. It then engagesa 28 kW drilling machine to drill a holein the wall, up to 20 meters in depthand 76 mm in diameter, into whichstabilizing rods are inserted. The drillcan penetrate any rock-hard material,on any gradient.

According to a project coordinator,“Assuming a typical landslide front of5,000 square meters and requiring5,000 meters of deep drilling, we estimate that the Roboclimber systemcan save 75,000 euros (about$100,000.00 as of this writing),” as opposed to performing the reinforcement process manually. “Themost important factor is that, withRoboclimber, we can secure steep,rocky walls without risking humanhealth and lives. We can do it faster,more efficiently, and yet much moresafely.”

RHex Learns to SwimBacked by $60 million in funding

from the Defense Advanced ResearchProjects Agency (DARPA, www.darpa.gov), the insect-like RHexrobots have been around for severalyears, crawling around and multiplyingwithin a number of universities.

The autonomous hexapod critter —patterned after the esteemed cock-roach — was created as part of a studyin computational neuromechanics that“applies mathematical techniquesfrom dynamical systems theory toproblems of animal locomotion and, in turn, seeks inspiration from biologyin advancing the state of the art ofrobotic systems.” Translation: Theywant to figure out how roaches canwalk without falling over.

RHex is a pretty successful concept, and current versions canmove at better than five body lengthsper second (2.25 m/s), climb slopesexceeding 45 degrees, and climbstairs.

Possibly the most fascinatingincarnation so far was created atMcGill University's AmbulatoryRobotics Lab. A waterproof versionwas dropped into a reef environmentand remotely controlled with the helpof two on-board cameras. The “Aqua” RHex showed impressivemaneuverability in the underwaterenvironment. To view underwatervideos and access some relevant links,seewww.cim.mcgill.ca/~arlweb/robots.html General info is availableat www.rhex.net SV

RRoobbyytteess

Roboclimber prevents landslideswithout endangering human life.

Photo courtesy of D'Appolonia S.p.A.

Aqua — an adaptation of the RHexrobot — dons flippers and takes

to the ocean. Photo courtesy of McGill University.

66 SERVO 03.2005

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SERVO 03.2005 67

TThe smallest of robots can be builtby only using a thin sheet of

aluminum or plastic. Just stick motorsand other parts to it and you have arobot. You can even build simple robotbodies using only an electronic circuitboard or solderless breadboard. Aslong as the batteries and motors aren’t too heavy, these constructiontechniques will provide many hours

of robot playtime with little cost andconstruction time.

Larger robots, however, need astronger framework, as larger motors,batteries, wheels, and other parts addweight. To support this weight, yourrobot needs a reliable structure — thebones of the bot.

Fortunately, building strong robotbodies isn’t difficult or expensive, and

you can find much of what you need atthe local hardware store. Mail orderprovides an even greater assortment of unique parts, such as extruded aluminum framing.

In this column, I’ll discuss buildingrobot structures using traditional fram-ing techniques with simple steel and plastic brackets, metal stock, andaluminum extrusions.

by GGordon MMcComb

RoboResources.qxd 2/2/2005 10:06 AM Page 67

Steel Brackets to BoltThings Together

Brackets are used to hold two ormore pieces together usually (but notalways) at right angles. Hardware brack-ets are ideal for general robotics con-struction, as these brackets are availablein a variety of sizes and styles. You canuse the brackets to build the frame of arobot constructed with various stock.

The most common brackets aremade of 14- to 18-gauge steel (thelower the number, the thicker themetal). In order to resist corrosion andrust, the steel is zinc plated, giving thebrackets their common “metallic” look.(Some brackets are plated with brass,and are intended for decorative uses.They’re more expensive and they havelimited use in robotics). Common sizesand types of steel brackets are:

• 1-1/2 x 3/8 inch flat-corner brackets— used when joining pieces cut at 45°miters to make a frame.

• 1 x 3/8 or 1/2 inch corner-angle brack-ets — used when attaching the stock tobase plates and when securing variouscomponents (like motors) to the robot.

• The above also come in sizes up toabout 2 x 2-3/4 inches.

Keep in mind that angle bracketsare made of fairly heavy steel and are,therefore, heavy. If you use a lot ofthem, they can add considerable weightto your robot. If you must keep weightdown, consider substituting angle brack-ets with other mounting techniques,including gluing, brazing (for metal), orfastening screws directly into the frameor base material of your robot.

Most brackets are pre-drilled toaccept #6 to #10 size machine screws(you can use wood screws if you’reattaching the brackets to wood). Forsmall robots, choose a smaller fastenersize — it’ll save weight. A good all-purpose machine screw for most hobbyrobots is 6-32. The “6” means it’s a size#6 fastener, and “32” means there are32 threads per inch. Choose the screwlength to accommodate the material you

are fastening together. Common lengths(in inches) are 1/2, 3/4, 1, and 1-1/2.

Using SpecialtyFurniture Brackets

The better hardware stores stock asmall assortment of replacement partsfor shelves, cabinets, and furniture.Among these parts are several sizes andstyles of brackets made of either metalor plastic. In my local hardware store,these parts are socked away in little yellow drawers. You buy them in singlequantities and prices are a little high.

Another source of handy bracketsfor robotics is the local cabinet-makingshop. Though reselling parts isn’t theirmain business, you never know what you can get unless you ask. Lookfor heavy duty “KD” (knock-down)brackets, which are used to lashtogether two pieces of heavy wood.With the right fastener, they’ll evenhold together heavy robots.

Along the same lines are catalogretailers of KD furniture such as IKEA.Check for availability of spare parts.Depending on the retailer, spare partsare only available as replacements forspecific products, so you must knowwhat to order before you can order it.One way around this dilemma is to finda piece of furniture in the store thathas the part you need. You can thenask if spare parts are available for it.

Remember, metal brackets canadd substantial weight to a robot.Plastic brackets add little weight, but —unless you’re careful — they don’t provide much holding power. Such isnot the case with “gusseted” brackets.

A gusseted bracket is made of plastic, such as high-density polyethylene(HDPE), which makes it very light. To addstrength, the bracket uses molded-in gus-sets that reinforce the plastic at its criticalstress points. The result is a bracket thatis about as strong as a steel bracket, butat only a fraction of its weight.

Alas, plastic gusset brackets arenot easy to find. They are availablefrom some furniture building outletsand select online resources, such as Budget Robotics. Sizes are fairly limited, but those sizes tend to be quiteadequate for most jobs.

Even more sources for brackets:

• Mirror clips (hardware store) can beused as small brackets. Most mirrorclips have only one hole and may notbe in the familiar L-shape. You canalways drill more holes and bend theclip to the shape you want.

• Small metal L-brackets (computersupply) are used to construct electronicsand computer systems. You’ll have better luck finding these online.

• Extra metal and plastic parts fromErector Sets and similar constructiontoys make for inexpensive brackets.

• Self-made brackets can be constructedfrom aluminum or brass metal, which isavailable at hobby stores and somehardware stores. Drill the holes, cut tolength, and bend as needed.

Metal Stock at theCorner HardwareStore

You can build a sturdy (nearly indestructible!) robot using the metalstock commonly available at most anyhardware store. A very handy materialis the “extrusion,” so called becausethe metal is produced by extruding theheated, molten material out of ashaped orifice. The metal cools in theshape of the orifice, which can be around tube, a square tube, and variousL, T, I, and U shapes. Metal extrusionscan be used to construct the frame ofa robot, for example, or to custom-make brackets and other parts.

Just about all metals are availablein extruded shapes, but — for the purpose of robotics — the three mostuseful extruded metals are:

• Aluminum, usually 6061 alloy,anodized with a brushed silver appear-ance. It won’t rust, but corrosion is possible if left outdoors. This material isreasonably easy to cut and drill and isaffordable. It’s available at most hardware stores in various sizes andlengths. A typical aluminum extrusionis a one inch equal L-angle; this means

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68 SERVO 03.2005


an L-angle shape is one inch on eachside. The typical thickness of aluminumextrusions is 1/32 to 1/8 inch. Lengthsare from short, one foot pieces to eightfoot ones.

• Mild steel, for general house andyard work. The steel is sold uncoated,can be welded, and will rust if notpainted. This material is suitable forlarger, heavy duty robots, such as thosemeant for combat. Typical thicknessranges from 1/8 to 1/4 inch.

• Brass and copper extrusions are available at some hardware and hobbystores in limited sizes and varieties.Most extrusions are round and squarelengths of tubing with thickness from1/64 to no more than 1/16 inch. You’duse these when you need lightweightmetal that can be soldered or brazed,such as constructing the legs of a smallhexapod robot. Brass and copperwon’t rust if left unpainted, but bothcan tarnish.

Extruded aluminum and steelcomes in even numbered lengths fromtwo to eight feet per section; somestores will let you buy cut pieces.Aluminum is lighter and easier to workwith, but steel is stronger. Use steel when you need the strength; otherwise, opt for aluminum.

Extruded aluminum and steel areavailable in more than two dozen common styles, from thin bars to pipesto square posts. Although you can useany of it as you see fit, a couple of standard sizes may prove to be particularly beneficial in your robot-building endeavors.

• 1 x 1 x 1/16 inch angle

• 57/64 x 9/16 x 1/16 inch channel

• 41/64 x 1/2 x 1/16 inch channel

• Bar stock widths from one to threeinches and thickness from 1/16 to 1/4 inch.

Perhaps the most common application for metal extrusions isbuilding sturdy robot frames. As notedabove, common shapes are the U- andL-channel; the U-channel is my personalfavorite. A handy size is approximately1/2 x 1/2 x 5/8 inch — large enough toaccommodate fasteners, L-brackets,and other hardware, but not so largethat the metal unnecessarily adds tothe weight of the robot.

To construct a frame, the extrusionis cut to length, then joined either toitself or by way of brackets. Metal orplastic fasteners can be used, as needed.For a lightweight robot, use eithernylon fasteners (if the frame is fairlysmall, say under eight inches) or 4-40steel machine screws. You can also substitute aluminum pop rivets ratherthan screws, but this naturally makesthe frame construction permanent.

Weight can add up quickly whenusing brackets, so choose the smallestavailable that is consistent with theoverall load bearing on the frame. Extra

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large steel L brackets are not necessaryfor a robot under about 12 to 15 inches. Opt instead for the smaller 1 x1 x 1/2 inch steel brackets or plasticbrackets.

Mending Plates andIron Angle Brackets

The typical wood-frame home uses

galvanized mending plates, joist hangers, and other metal pieces to join lumber together. Most of thesecome in weird shapes, but flat platesare available in a number of widths and lengths.

You can use the plates as theycome or cut them to size. The materialis galvanized steel and is hard to cut, sobe sure to use a hacksaw with a freshblade. The plates have numerous pre-drilled holes in them to facilitatehammering with nails, but you can drillnew holes where you need them.

Mending plates (sometimesreferred to as Simpson ties — after thename of a major manufacturer) areavailable in four, six, and 12 inchlengths that are four or six incheswide; they are also available in twoinch wide T shapes. You can usuallyfind mending plates, angles, and othersteel framing hardware in the nail andfastener section of home improvementstores.

Ready-made steel angle bracketsare convenient and cheap for the bulkof any robotics project.

Sometimes, you need a size orshape that’s just not available at thecorner hardware store. Other times,the typical steel bracket is too heavyand an aluminum version would beperfect — only they don’t have manybrackets in aluminum. The solution:Cut your own brackets out of metalextrusions.

Most brackets have one or moreholes per “leg,” so start by drilling theholes you’ll need to mount the bracket.Remove any burrs or flash around thedrill holes. Once drilling is complete,mark off the metal for cutting. An electric chop saw makes this job easy,but a hack saw and miter block canalso be used.

Be careful! By their nature, bracketsare small and dangerous to cut on anelectric saw without using some form ofclamp to hold them down. Clamp theextrusion on both sides of the blade. Asmall C clamp or spring-loaded clampshould be sufficient. The idea is to usethe clamp and not your bare fingers tohold the small bracket while it’s beingcut from the main piece. Cut off themetal, not your fingers!

70 SERVO 03.2005

Robotics RResources

FIGURE 1. Ace Hardware stores dot the country and provide a horde of useful bits and pieces for robot construction.

FIGURE 2. Home Depot’s Maintenance Warehouse is the mail order arm of the gigantic Home Depot.


Even More HardwareStore Finds

Let’s take a virtual stroll down theaisles of a well-stocked hardware store.Here, you’ll find plenty of parts you can usefor your robot creations. It’s impossible tolist all of the goodies you’ll likely spotand even less practical to discuss everyconceivable use, but here’s a sample listto get your creative juices flowing:

• Rubber grommets protect wiring,but also act as springy material forwhiskers, sensors, and linkages.

• Cable clips for wire and small pipingand tubing (e.g., aquarium tubing) areuseful for wiring containment, as wellas attaching parts (small motors, sensors, etc.).

• In addition to electrical applications,use large wire terminals for crimpingcables for grippers and leg mechanisms.

• Springs have 1,001 uses, such as intouch sensors, bumpers, and evenrobot decoration.

• Rubber and metal feet for small furniture and appliances make idealwalking pads for legged robots.

• Use metal conduit and EMT fittings

found in the electrical section to make avery heavy duty frame for a larger bot.

• Shower and patio door parts includerollers (nylon, ball bearing) for use assmall casters and wheels.

• Weather stripping and rubber doorinsulation are perfect for robotbumpers.

SourcesAce Hardwarewww.acehardware.com

This is an independently-ownedchain of hardware stores. In my experi-ence, a number of the Ace Hardwarestores I frequent have a number ofproducts not carried by the “Big Guys”(Lowe’s and Home Depot), such as

Robotics RResources

FIGURE 3. Lowe’s home improvement stores offer a number of specialty parts in their hardware department.

SERVO 03.2005 71


unusual fasteners and hardware. Don’toverlook the small stores in your areafor unique components for yourrobots. Ace has store locations acrossAmerica and in 70 other countries.Check the website for a store locator.

American Science & Surpluswww.sciplus.com

Realizing that robot building is animportant aspect of their business,AS&S dedicates a special section torobot parts. Find the Robot Parts link inthe table of contents area of their website and you’ll find the latest offerings. When I last looked, they hadball transfers (great for robot supportcaster wheels), large heavy dutywheels, pneumatic cylinders, rollerchain, and more.

Aubuchon Hardwarewww.aubuchon.com

Online and local Aubuchon storesdot the Northeast. The online catalogboasts over 70,000 items. Productsinclude hand and power tools, fasteners,hardware, plumbing, and electrical.

C & H Saleswww.candhsales.com

C & H sells motors, gears, pneumat-ics, pumps, solenoids, relays, and lots ofodds and ends. Their catalog regularlycontain dozens of quality surplus DC(geared and non) and stepper motors.

CornerHardware.comwww.cornerhardware.com

Now, you can go to the hardwarestore using only your computer.CornerHardware.com is like the neigh-borhood hardware store, except it’sopen on Sunday. Their inventory includesplenty of brackets and other parts.

Home Depotwww.homedepot.com and Home Depot MaintenanceWarehousewww.mwh.com

Home Depot has a printed catalogfor maintenance and repair supplies —a big one — with lots of pictures, illustrations, and specifications. It’sideal for figuring out exactly what youneed for your bot. Depending onwhere you live, same day or next dayshipping may be available to you; otherwise, you’ll wait two or three daysto get your stuff. Use the locator at thesite to find a warehouse near you.

Lowe’s Companies, Inc.www.lowes.com

Lowe’s is an alternative to HomeDepot with a selection of fasteners andother hardware through retail stores andonline sales. Check the web page for astore locator. Lowe’s has 600+ super-stores in some 40 states. The site includesa “how-to library” on home repair andremodeling. I looked ... nothing aboutbuilding robots. Still, some of the articlesmight be useful to learn about materialsand tools and the best way to use them.

Rockler Woodworking andHardwarewww.rockler.com

Rockler carries hand and powerwoodworking tools, hardware, andwood stock (including precut hardwoodplywoods). Among important hardwareitems are medium-sized casters, drop-front supports (possible use in bumpersor joints in robots), and drawer slides.

Small Parts, Inc.www.smallparts.com

Small Parts stocks a variety of components, including a large inventoryof fasteners.

True Value Company Corporationwww.truevaluecompany.com

True Value Company is the corporate parent of a number of hardware stores, home improvementcenters, and industrial supply outlets.

• True Value — Major hardware storechain in the US: www.truevalue.com

• Induserve Supply and CommercialSupplies — 210,000 items for small tolarge businesses: www.induserve.com and www.commercialsupplies.com SV

72 SERVO 12.2004

Robotics RResources

Gordon McComb is the authorof several best sellers. In addition,he operates a small manufacturingcompany dedicated to low costamateur robotics, www.budgetrobotics.com He can be reached [email protected]

AUTHOR BIO

FIGURE 4. Use the store locator feature at the True Value website to find a store near you.


In 2004, robot builders came from around the worldto San Francisco, CA to meet the Americans in the first-ever Robot Olympics — ROBOlympics. From March24-27, 2005, they’ll be returning to San Francisco StateUniversity to compete again, with more robots frommore countries and more competitions. Will you be joining them?

While robot competitions are held throughout theworld, competitions tend to be singular in nature, suchas Robot Soccer in Pittsburgh, PA or Fire Fighting in LosAngeles, CA. ROBOlympics is a unique event, offeringrobot builders a chance to meet their peers from acrossthe world and with many different styles of robotics.Many builders outside of Japan have never seen Robo-One before, but will be quickly inspired by the Asianandroids, much as they were when 11 contestants flewin from Tokyo last year.

The goal is not to hold the biggest robot eventever. The goal is to get builders from all countries andall fields of robotics to meet each other. In last year’scompetition, the Americans swept the combat robotcategories, while the Japanese took home all themedals in the Robo-One events and the three-kilogramsumo classes.

Robot Soccer — probably the most difficult of allrobot competitions — is a major part of ROBOlympics.Last year, the top contenters — Korea and Japan — wereupset by Slovenia (the Cinderella surprise team). Thisyear, we’ve added Aibo soccer. If you can get four Aibostogether, you can play, too!

Of course, there is Robot Combat. Robots weighingas much as 240 pounds cut, burn, turn over, and destroythe other robots behind bullet-proof glass, while theaudience screams in both delight and fear.

Last year, the Americans swept the class; this year, with several experienced teams from Europe, SouthAmerica, Australia, and Asia, we can’t take a sweep for granted.

Fire is always a big crowd pleaser.

A clean sweep by the Robo-Ones!

by Dave Calkins

BBoott BBuuiillddeerrss GGeeaarr UUpp ffoorr tthhee SSeeccoonndd RROOBBOOllyymmppiiccss

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SERVO 03.2005 73

Menagerie.qxd 2/2/2005 1:02 PM Page 73

Ribbon Climbing — a new sport — involves solar-powered robots climbing a thin ribbon as fast as possi-ble. This competition is to help build interest in “TheSpace Elevator” — a new concept that involves sendingthings into space by a floating ribbon with an elevatorrather than via rockets.

Don’t laugh! It’s a viable concept. Jack Buffingtongot a gold medal and a trip to Washington, DC to pres-ent his robot to politicians, who are now consideringfunding a space elevator platform, a concept only firstproven to be feasible at ROBOlympics 2004!

The Fire Fighting competition may sound exciting,but it also has an admirable goal: build a robot that willturn itself on and put out a fire quickly. There are alsoline following robots, maze solving robots, and a host ofother categories.

Even the most famous robot in the world came in2004: R2-D2. He’ll be back in 2005 to entertain both theaudience and the competitors, along with Stormtrooperguards.

So, why let athletes have all the fun and get all theglory — join us at ROBOlympics! The 2005 InternationalUnified ROBOlympics Competition includes all of these exciting events, in addition to the established competitions:

Biped Race — This new event challenges competitors tobuild robots that can walk.

Robot Triathlon — Robots compete in a three-stage race:legs, wheels, and water.

The Line Slalom — Negotiate a 10-foot track without losing your way.

Ribbon Climber — Climb a ribbon with autonomouspower supplies.

RoboMagellan — Remember the Grand Challenge?Smaller scaled bots navigate across campus.Camp Peavy and his robot, Springy Thingee.

Combat robots too noisy for you? How about Robo-One

boxing for a change?

Silver medal winner A-Do willmake all the other Japanese

androids jealous.

74 SERVO 03.2005


Balancer Race — Two-wheeled balancing robots matchprogramming and balancing power.

Best of Show — Those bots that don’t fit into other class-es get their chance to shine here!

BEAM — Hack a Robosapien or build a junkbot.

Exo-skeleton — Both lifting and carrying. Sound familiar?

Robo-One — The coolest androids ever. They box, standon their heads, and open doors!

Art Bots — A fusion of hard science and artistic beauty.Four classes will amaze you.

Even if you can’t bring a robot, come to witness thelatest tech! See the website for full details: www.robolympics.net

Okay, all together now:“These aren’t the droids …”

Perform proportional speed, direction, and steering withonly two Radio/Control channels for vehicles using two

separate brush-type electric motors mounted right and leftwith our mixing RDFR dual speed control. Used in manysuccessful competitive robots. Single joystick operation: upgoes straight ahead, down is reverse. Pure right or left twirlsvehicle as motors turn opposite directions. In between stickpositions completely proportional. Plugs in like a servo toyour Futaba, JR, Hitec, or similar radio. Compatible with gyrosteering stabilization. Various volt and amp sizes available.The RDFR47E 55V 75A per motor unit pictured above.www.vantec.com

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He shakes, picks up cups,and can turn on a dime.

Johnny5 is alive!

The Hurosot soccerrobots play autonomous

soccer!


76 SERVO 03.2005

Occupying much of northern Chile, the arid Atacama Desert is such a harsh environment,rainfall is measured not in inches per year but in millimeters per decade. Here in the oxidant-rich soils, microscopic organisms struggle for existence, gleaning what moisture

they can from an occasional fog and adapting to convert high levels of UV radiation into usablesustenance. What sets this desert apart from any other in the world is that its characteristics arevery similar to that of Mars, and that makes it the perfect location for the astrobiologists fromCarnegie-Mellon University. Together with the support of several other universities in the US, theteam of scientists, along with an autonomous robot named Zoë (in Greek, it means “life”), maybetter understand how life might survive on other planets by first exploring the limits of life hereon Earth. More importantly, they'll learn how best to detect and analyze life.

Zoë on the Atacamaby Ryan Lee Price

How a Sliding Autonomous Rover Is Learning to ExploreNew Worlds by First Exploring Our Own

© 2

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Scientists also plan tomap the habitats of thearea, including its morphol-ogy, geology, mineralogy,texture, and physical andelemental properties of therocks and soil. With thisinformation, they hope todocument how life modi-fies to its environment,characterize the geo- andbio-signatures of microbialorganisms, and create scientific procedures onhow best to discover life.“Our goal is to make genuine discoveries about life and habitats in the Atacama and to createtechnologies and methods that can beapplied to future NASA missions,” saidDavid Wettergreen, an associateresearch professor at Carnegie-Mellon’sRobotics Institute. He is leading therobotics research team on the “Life inthe Atacama” project.

Robotic astrobiology is an importantmethod used to study how life canexist in such extreme environments.Because it is inconvenient, inefficient,or most times impossible for people todirectly study these various environ-ments found in the Solar System andhere on Earth, robots have been developed to collect the necessarymeasurements instead. Such a robot isZoë, an aluminum-frame rover nearlynine feet long and weighing in at over400 lbs., capable of operating completely autonomous or via remote.

Called sliding autonomy, Zoë cansmoothly adust from one method ofcontrol to another. For example, it candecide for itself how, when, and whereto perform a mission or function, but ifit detects strange behaviors from itssensors or it decides the mission isimpossible, it can send a help messageand stop to await further instructions.

Running on a bank of solar cellsthat generate nearly 600 watts and batteries that can store approximately3,000 watt-hours, Zoë follows the sunon its daily 1.5-mile missions around thebase camp in search of microorganisms.In order to identify even the slightesttraces of life, Zoë is equipped with toolsborrowed from other technologies ordeveloped specifically for its mission.

Fluorescent ImagerInstead of taking microscopic-scale

images of rocks and makinghours-long spectroscopicobservations (as the MarsExploration Rovers did) Zoë will test a novel life-detection strategy: Samplesof rock and soil will besprayed with a series of fluorescent dyes that lightup in the presence of life’schemical building blocks. Acamera equipped with special filters then wouldlook for the glow associatedwith DNA, proteins, carbo-hydrates, or lipids.

Some organisms fluoresce naturallywhile others can be made to do so with special chemical dyes. These dyesare carefully engineered to fluoresceonce attached to specific organic mole-cules. The excitation and emissionwavelengths of these dyes can bemade to vary and thus be distinguish-able from one another. Zoë will beusing four different dyes to identifyproteins, lipids, carbohydrates, andDNA. It will be programmed to do spotchecks of target sites, as well as inch-by-inch surveys of a stretch of desert.For this year, scientists will be standingbehind Zoë, spritzing the fluorescentdyes onto rocks and soil for Zoë tocheck with its camera. Eventually, thespritzers will be built into the rover.

Fluorescence occurs when a substance absorbs light of one wave-length and emits light of a longerwavelength. At an atomic level, this

Opposite Page: Life on the AtacamaDesert is harsh and desolate forman and machine.

Top: Because of the distance factor,Zoë had to be built at the camp.

Right: At the top of its mast is the majority of the sensors andlandscape cameras.

Zoe.qxd 2/2/2005 1:43 PM Page 77

78 SERVO 03.2005

phenomenon occurs when an electron absorbs the energy froman incoming light photon andjumps to a higher energy state.Since this excited state is unstable,the electron will eventually returnto its natural state, and in doing so,release energy as heat and light.The emitted light has a longerwavelength, lower frequency, andless energy because some of theenergy is released as heat.

The fluorescent imager providesvisible and fluorescent images oftargets underneath the rover, in anapproximately 8 x 6 cm area. Theimages are used to identify life bydetecting naturally fluorescent organ-isms, primarily chlorophyll, but possiblyothers, such as carotenoids.

The bottom of the electronics box is a Fresnel lens, on which aremounted red, green, and blue LEDs,which are all focused on a central areaunderneath the imager. A hole is cutin the center of the lens, and threeinexpensive off-the-shelf RGB web-cams sensitive to light from 400,950nm are pointed down through thehole. One camera is unfiltered; theother two have a 665 longpass and a700/75 bandpass filter, respectively.The main rover processor can switchthe LEDs and control image capturefrom the three cameras.

When all three LED colors are

activated, a normal reference image iscaptured with the unfiltered camera.However, using only a single color ofLED and capturing from one of the filtered cameras provides a fluorescentimage. Changing the LED color and filter allows detection of different fluo-rescent signals, but the signal of greatestinterest is chlorophyll (the molecule inplants and bacteria that performs photosynthesis), which returns a strongred fluorescent signal under blue illumination and the 700/75 filter.

PlowSince some organisms may not be

living on the surface, Zoë will beequipped with a simple plow-like device toflip over rocks and expose subsurface

soil. Stored in the underbelly, theplow will be lowered to the groundand held in place while the robotdrives forward, thus digging asmall trench. The fluorescenceimager and spectrometer wouldthen be used to examine the newlyexposed surfaces.

Visible/NearInfraredSpectrometer

Zoë will be equipped with avisual/near-infrared spectrometer

tuned to detect chlorophyll or the con-version of light energy into chemicalenergy that can be used by biologicalsystems.

A spectrometer works by analyzingthe light reflected from a sample, andit was discovered that the reflectedlight contains a great deal of informa-tion about the atoms contained withina sample. Just like everyone has aunique fingerprint, each atom has particular wavelengths of light that itreflects, called its emission spectrum,and a complimentary set of wave-lengths that it absorbs, called itsabsorption spectrum. By spreading thereflected light out into a spectrum —much like a prism creates a rainbow —the spectrometer can measure theintensities of light at different parts of

Above: The plow scrapes away thetop soil before closer examination ofpossible subterranean life.

Left: Back at Carnegie-Mellon, Zoëhas its solar panels removed for maintenance.

Though obvious to us, detecting organismssuch as this is still difficult for Zoë

in real-life conditions.

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the spectrum and thus detect whatatoms are present. Zoë's spectrom-eter will only look at visible and near-infrared light, which constitutes only a small portion ofthe entire light spectrum. Inincreasing frequency and energy,the forms of light include radiowaves, microwave, infrared, visible,ultraviolet, x-rays, and gamma rays.

Location SensorsOn the low-tech side of Zoë,

it is able to observe commonweather occurrences and detectvarious levels of sunlight to supportresearch on the habitat of any organisms found. It is able to measuretemperature, pressure, humidity, wind,insolation and UVA/UVB light.

Panoramic ImagerThe stereo panoramic imager

cameras provide high-resolutionimages and allow three-dimensionalreconstruction of the landscape to beused to plan local traverses and scientificoperations by the rover. The camerasare mounted on a pan-tilt unit atop a2.5-meter mast near the front of the robot, allowing them to viewapproximately 180 degrees in front ofZoë. Each camera returns a 1,280 x960 color image, with a horizontal field

of view of 21.1 degrees, correspondingto a footprint of about one squaremeter when pointed at the groundnearby. In selecting the camera designbefore the first Atacama expedition,the main driver was the project’s tighttight schedule, which forced the teamto borrow as much as possible from anexisting design, in this case the Pancamdeveloped for the Mars ExplorationRovers (MER).

The most visible and accessiblesigns of life was in the coastal rangearea of the Atacama where lichenswere present on the surface of rocks.Their presence or absence varied. Insome areas, they were found on nearlyevery rock, but in others, they werecompletely absent. Individual lichensare small, rarely covering an area

larger than 50 cm. Their colorationvaries widely, from rare bright yellow and orange specimens tomore common greens and grays.

The Future of Zoë Carnegie-Mellon's operations

for Zoë will be based at SalarGrande, a salt flat near the city ofAntofagasta, near the west coast.“It's quite barren,” Wettergreensaid. “It's not like the SaharaDesert, where you have shiftingsands. There's really just soil androck. It is sort of reddish in color,

so I guess in some regards it may beMars-like. Actually, when the light isgood, early in the morning and in theevening, it’s quite beautiful there — butit is profoundly empty.”

Zoë is by no means the first CMUrobot to travel in the desert. Two otherrobots — Hyperion and Nomad — havehelped make a robot like Zoë possible.Besides validating the concept of a sun-tracking robot, Hyperion served as atestbed for technologies that are usedon Zoë, while Nomad was originallydesigned to search for meteorites inAntarctica. The technologies used onthese projects raised the bar forautonomous, long-distance traverses.Will Zoë ever see the horizons of a dis-tant planet? Probably not, but a distantcousin of Zoë most certainly will. SV

Above: The conditions aren’t ideal, but team membersDaniel Villa and Stuart Heys make the best of it.

Right: Zoë can traverse most any obstacle in theAtacama Desert autonomously, and if not, it’s programmed to find a way around what is blocking its path.

Cameras not only capture real images, butthey provide a host of environmental data.

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So You Want to Build Robots?

It’s always funny to see how people react to the

unexpected. The other day, Iwas talking to a few of mycoworkers about a robot proj-ect that was just entering thedesign stage. A principal scientist from a differentdepartment walked over andgestured to us, remarking,“So, these are the roboti-cists!” Everyone looked ateach other in bewilderment,and with nervous laughs, wereplied: “I’m just a physicist.”“I’m a special effects engi-neer.” “Me too!” But theunavoidable truth, as justrevealed, was that 10 years ofrobot building — machining,welding, wiring, programming — hadtransformed all three of us into some-thing different: roboticists — one of thehot job titles of the next two decades.

I receive four or five emails everymonth from students who are wondering how they can becomeroboticists. But before I can answerthat question, a more fundamental discussion of exactly what constitutes arobot must ensue. Everyone has a different idea, and scores of USENETflame wars have been devoted to this(apparently) perplexing question.

In 1979, the Robot Institute ofAmerica wrote a definition that included a core requirement for a robotthat most people miss, that of reprogrammability. If a machine is programmable, that program shouldbe alterable in order to qualify it forrobotic status. (Note, that this alsoopens up the possibility of self-repro-gramming robots, a favorite topic of

SciFi authors and Ph.D. candidates.)It’s probably safe to also say that

robots have three main functionalparts: a sensor, a processing unit, andan effector. The sensor reads someparameter of the world — sound, light,the presence of an obstacle, depth, orspeed. The central processing unit uses those measured parameters in aformula (or algorithm) to create anoutput that then affects change in theworld by moving, diving, making asound, or blinking a light. Each of thethree parts requires certain disciplinesof study in order to develop a goodworking knowledge to, well, let youwork with them. I’ll cover a few thatare less obvious, yet important to thejourney.

SoftwareAlthough there are mechanically

(hard) programmed robots in the

world, by far the most com-mon is the soft programmedvariety. For this, you’ll need tolearn some sort of computerlanguage that corresponds tothe CPU in the bot, your development tools, and yourbudget. Many people incorrectly think that fastercomputing makes for betterrobots. The truth is that cleverlythought-out abstractions andalgorithms make for goodrobots. Don’t be fooled into a fealty for a particular language or CPU. Your goalshould be to develop the skillsto solve problems with thecomputing lump at hand.

Material ScienceI can’t stress the importance of

learning about materials nearlyenough. What makes a piece of steelhard? What makes it tough? Whenshould you ditch steel and use aluminum or even wood? The best wayto learn about materials is to work with them and develop an intuitiveknowledge for selecting and designingwith them. This weekend, go to your local home improvement store,get some raw materials, and buildsomething. Then break it. You’ll learn alot from the process.

ElectronicsYou can’t know too much about

analog and digital circuit design andoperation. It’s true that, today, thereare more off-the-shelf parts available towire up robots than ever before. Just

by Dan Danknick

Appetizer.qxd 2/3/2005 3:27 PM Page 80

because you can un-box and plug it in,however, is no reason against at leastunderstanding the principles by whichit works. If you go back through olderissues of SERVO and read the questionsthat Mr. Roboto fields, you’ll see thatmany of his answers start by teachingthe theory behind various electronicdevices.

FasteningI know this looks a bit out of place,

but it isn’t. Learning how to bolt, weld,or cast things into existence is a realcore of robotics, especially if youexpect those creations to have any sortof lifetime in the real world. It’s staggering to discover all of the wayswe’ve come up with to attach materialX to material Y. The pages of SERVOare rich with information on this, so

don’t gloss over those features!

Failure AnalysisThis is a powerful topic that many

people don’t see the need for. Heck,who expects their robot to fail? Howyou analyze a failure and craft a solu-tion is, in many ways, the summationof many of these disciplines. If a sensorsystem isn’t working, should you fix themechanical mount, tune the electronics,or write a software filter for the data?It’s not unusual for the answer toencompass a bit of each, but youwon’t know that unless you reallyunderstand the nature of the problem.

If you’re a student about toembark on a future of robotics, theworld is wide open to you. Take everyclass you can, find mentors who knowmore than you, and strive for diversity

in your knowledge. One of the projects I am working

on right now relies on human/robotinteraction. By the time it is done, all ofmy machining and welding skill may beovershadowed by what I learned in ahuman factors class: This robot maywork best if the operator is simplyallowed to learn to work with it.

In the early days of computers,there were no software engineers.There were chemists, physicists, andmathematicians who used this newcomputing invention as a tool to gettheir work done. The more programsthey wrote, the more they discovered,and the more they helped the technol-ogy develop. One field of studyspawned a new one. So don’t be surprised the day someone pointstoward you and says, “Hey, let’s ask theroboticist!” SV

Because the art of building a robot is so diversified,skills and knowledge of a wide range of fields is

necessary, such as working with metal and plastics.

On the other side of the spectrum, knowledge of hardware, software, and electronics are all

a hefty requirement.

Advertiser IndexAll Electronics Corp. ............................19

Cleveland Institute of Electronics .......11

CrustCrawler .........................................13

Custom Computer Services, Inc. ..........9

Hitec ......................................................29

Hobby Engineering ..............................16

Jameco ..................................................83

Lemon Studios .....................................33

Lynxmotion, Inc. ...................................45

Net Media ...............................................2

NUBOTICS .............................................19

Parallax, Inc. ...........................Back Cover

PCB123/PCBexpress ...............................3

PCB Fab Express ...................................54

Pololu Robotics & Electronics .............27

ROBOlympics .......................................63

Robotics Group, Inc..............................57

Robotic Trends .....................................17

Smithy .....................................................19

Solutions Cubed....................................69

Sozbots..................................................62

Technological Arts ...............................71

Vantec ...................................................75

Zagros Robotics ...................................19

SERVO 03.2005 81

Appetizer.qxd 2/3/2005 3:28 PM Page 81

82 SERVO 03.2005

Many of us who are old enough to remember the EICOand Heathkit electronics kits may remember the day that

Heathkit brought out the first robot kit — the Hero 1. I waspart of the newly-formed Southern California RoboticsSociety back in 1978 (later re-named the Robotics Society ofSouthern California) and were meeting in the Norwalk, CAcity library when a member mentioned that he had heardabout Heath mulling over a kit-built robot. A few yearspassed until 1981, when we had a representative from Heathgive a presentation of the Hero 1 at our meeting. It was aninstant hit with the members. The Hero (Heath EducationalRObot) was in full production the next year.

Based on the Motorola 6808 microprocessor, it was anideal teaching tool for many aspects of electronics. It had a“massive” four K of RAM and eight K of ROM that containedthe “robot monitor” — a good preparation for the PIC andsimilar microcontrollers with tiny memories that were tocome years later. The robot also had a flimsy and strangelyconfigured arm with a gripper that was surprisingly adept atmany object-manipulating tasks.

Hero also had an ultrasonic motion and range detector,sound and light sensors, a 17-key Hex keypad to enter pro-grams, and an experimenter’s board all on its head, whichcould rotate almost 360°. A nice feature was its ability tospeak to people who were programming or interacting withit. It could even download and store programs on its cassettetape drive. Unlike the more popular differential “tank drives”on most experimental robots today, Hero used two fixedwheels and a maneuverable front drive wheel. Weighing inat 39 pounds with its four six-volt gel cell batteries and stand-ing 20 inches high, it also came with a charger and teachpendant. It could drive you nuts when it frequently broke

down, but could alsoentertain and teach youfor hours and hours.

With the success ofthe original Hero 1,Heath came out with astripped-down versioncalled Hero, Jr. It had noarm and no movingupper torso and wasmore of a security deviceand alarm clock thatroamed about thehouse. It had 32 K ofROM that stored a fewsongs, such as “Daisy”

(remember HAL in 2001?) and could play a few games, avoidobstacles, and seek out people with its sensors.

The most sophisticated Hero was the Hero 2000, a 78-pound, 33-inch-high, well-designed machine with a 16-bit8088 master microprocessor and 11 eight-bit peripheralprocessors, 64 K of Basic ROM, 24 K of RAM (expandable to576 K) and an optional six-axis arm that had real capabilities.The Hero 2000 also had a remote RF-linked console thatserved as a program input device or a basic controller and anautomatic docking/charging capability. The arm could bepurchased separately as a training device, as could a very nice“Robotics and Industrial Electronics” course that came in twothree-inch-thick notebooks. I still have this course materialand refer to it.

Considering that these robots were designed over aquarter of a century ago, their capabilities are still amazingto this day. Sadly, Heathkit Educational Systems and all of Heath was dissolved in the mid 90s and another Michigan company — Mobile Ed Productions — took over therights and the few robots and parts left for their teaching.The fantastic educational challenge aside, people just did notwant to build complex electronic equipment from kits whenthey could buy them assembled for much less. If any of you readers still have any of these robots, I suggest that you hang onto them. They were the first “crown jewels” ofexperimental robotics. SV

THE HEATH HERO ROBOTSby Tom Carroll

Yesterday’s Technology Points Us Toward Tomorrow

Carroll.qxd 2/3/2005 4:18 PM Page 82

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CoverInside.qxd 2/7/2005 4:19 PM Page 2


Vol. 3 N

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Servo Magazine 03 2005