MENG 185 Final Report

8/14/2019 MENG 185 Final Report

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Final Report

MENG 185

Nathaniel Kan

Robot Name: G-UNIT

A. Basic Description of Functionality

G-UNIT was originally designed with the intent of building the most robust design

possible. Ultimately, this did not turn out to be the optimal competition strategy. However, the

goals laid out in the initial development and planning stages were ability to navigate effectively

and precisely through all three terrains, deactivate mines by disarming for maximum points, and

remove mines for the point multiplier. The means with which these goals were accomplished are

as follows.

1. Mobility

The most important design aspect of G-UNIT's mobility is its wheels. A separate motor

controls each wheel independently. The wheels are notched, to allow movement on thegravel and climbing of the steps. A later addition was the insertion of metal protrusions

into the wheels, which allows better mobility on the gravel and step terrains.

The back end of G-UNIT's chassis is supported by a curved piece of sheet metal, toprovide little friction allow the back end of the robot to be dragged up the step terrain

without catching on the steps. Experimentation showed that in order for G-UNIT to climb

the final fourth step of the mountain, it was necessary to place an actuator to raise the

back end of the robot by pushing down the curved sled piece.

2. Disarming

G-UNIT's disarming mechanism consists of two parallel long thin beams, connected intogether in the middle by a hinge. The end of the beams protrude past the front wheels.

The two beams have a V shaped notch at the ends, and are made out of foam and metal

bonded with epoxy for strength. G-UNIT would be steered into a position so that the top

knob of the mine is in the notches, and then the top beam acts as a lever arman actuator

pulls the back end down, forcing the front notched end up and in this way popping up the

switch on the mine to disarm it. The actuator runs along the bottom shaft, and is

connected to the back end of the top shaft by a zip tie. The third motor is used to control

the height of the disarming arm, by rotating a sprocket with a protruding shaft parallel to

the motor's drive shaft. This shaft controls the maximum height by rotating the bottom

beam about a second hinge connected to the main robot chassis.

3. Removing

A half circle of PVC is connected to the front of G-UNIT, to allow the robot to push

deactivated mines off the board, after the arm is used and raised out of the way.

B. Performance

Mobility was excellent on the gravel, especially in terms of speedno robot was faster

than G-UNIT. The metal protrusions on the wheels made turning and movement on the ice


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slightly slower, however, precision movements were still an option, and overall the wheels did

quite well on the ice and gravel terrains. The step climbing function was somewhat less reliable.

G-UNIT was able to ascend the first three steps easily, but had trouble climbing the final step,

hence the need for the back-end raising actuator. With the actuator it was able to climb the final

step from straight on, however, raising the back end caused instability (G-UNIT is a tripod), andincreased the chance of tipping over (which happened in the competition).

The disarming function worked better before the competition than in the competition.Before the competition the disarming feature was working as it was supposed to, however, later

on more of the actuator's power was being lost when being transferred to the motion of pulling

down the back end of the top beam. I believe this was because of increased friction in the zip tie

due to wear. This loss of power caused some of the mines to require several attempts before

deactivation was successful. Also, there were problems adjusting the height of the arm, as fine

adjustments were not possible with the third motor control. When the device was being built, I

didn't realize that the third motor could not be controlled variably. All of the mines G-UNIT

accidentally detonated in the competition were due to the arm lowering too quickly and tilting

them. A better system for those controls would probably have been using the third motor to

control the winding and unwinding of a string which controlled the height.

Removing the mines from the game board worked as planned. The power in the wheels

was sufficient to push the additional load of the mines.

C.

Given a second chance, I think I would have done things much differently. One robot inthe competition used a wheel made out of an X shape of sheet metal, and this wheel was able to

climb the mountain very well, while still being able to move on the other terrains. I would have

incorporated this into my robot. I would also have made my deactivating system using the

magnet, as the magnet sensor was a lot more sensitive than I had previously believed and this

seems to now be the quickest way to deactivate mines for the large point score. I would also have

made a gripping device for carrying the mines off the boardI had originally intended to do this,

but could not find a way to do so on my robot given the space available. The most effective way

of gripping the mine that I observed was a motor/actuator combination that rotated a hook intoposition and then pulled the knob of the mine tight against the robot with the actuator. I believe

this could have been implemented effectively in G-UNIT.

D. Competition

G-UNIT did not perform well in the competition. The main problems were the failure of

the disarming arm to adjust to the correct height slowly, and a lack of practice on the game board.

Too many mines were set off accidentally. Furthermore, my initial strategy (in the first round

especially), did not suit G-UNIT 's robust design. I had originally intended for G-UNIT to in

direct competition with the opposing robot, where its superior mobility would allow it to blockthe other robot from mines that it would easily get. In most rounds, the two robots would get as

many mines on their own sides as possible before coming into contact with each other. Thestrategy I adopted at the end, which I think was an optimal strategy for play with G-UNIT, was to

go directly for the opponents ice mines, as those were the mines that most opponents could easily

get. I think my campaign would have been much more successful had I adopted this strategy early

on in the competition.

E. Deciding Factors


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I think two factors were critical in effective robots in the competition: robot mobility, and

the efficiency of the disarming mechanism. I noticed many of the robots that scored very well had

very quick methods of disarming the mines. The magnets seemed very effective at this, as did

safing mechanisms, as there is much less risk of setting the mine off with these types of

disarming devices. I also noticed that robot mobility was very importantin order to outscore anopponent often times a robot had to be able to disarm mines in at least two terrains. G-UNIT was

effective in its mobility, however, its disarming mechanism gave up too many accidental"explosions."

F. Lessons

I went through about sixty hours, all my materials (and a lot of scrap), and about thirty

iterations of my ideas in building my robot. The two biggest lessons I learned were 1) keep it as

simple as possible, and 2) do not build the chassis out of the cardboard stuff. The first lesson

came up when building my first design, which I eventually scrapped. I tried to incorporate an

elaborate chain mechanism to control the wheels, however, due to the inevitable errors in hand

machining parts for a novice, and the complexity of the design, when the final product was ready

for testing the small errors in each link in the chain of motion combined to make it almost

impossible to move straight. I later adopted a much simpler design of having each wheel directlyconnected to the drive shaft of the motor, which cut out many of the links in the chain and made it

a lot easier to build.

The second lesson also came up in my first design. My original chassis was cut from the

cardboard, which began to deteriorate as soon as I started to cut it. The structural strength of thematerial was also lacking, and in the end I switched to making an aluminum chassis.

G. Performance

I believe I attempted to build a "risky" design. In designing my robot, I wanted to build a

robot that would be able to traverse as many kinds of terrains as possible: the mountain, the

valley, the gravel and the ice. In the end, I think I may have attempted too much, my robot was

somewhat effective at some terrains, and very effective at others, but a master of no terrain. Inbuilding a robot that would attempt to be able to enter the valley, I sacrificed the option of

making my robot more than eight inches wide, which I could have used to make larger wheels

which would have been more effective on the other terrains. Likewise, there were height and

center of mass limitations I had to obey to make a robot that could climb the mountain. In the

end, I think only one other student built a mountain climbing robot.

My design worked the way I hoped in some aspects, and did not meet my expectations in

others. It was effective at moving on the gravel and ice, but climbing the mountain was too

difficult to be an effective strategy, and likewise with entering the valley. Also, controlling the

height of the arm was too difficult for a competition robot.

H. Scheduling and Planning

My robot was built right on schedule, and not a minute early. The only thing I should

have accounted for that I failed to was that other people would be practicing, and so I wasn't able

to practice as much as I had wanted to. I started working on my robot the week after spring break,

and went through many, many iterations of it. I built a lot of parts I ended up not using after

practicing with them and finding them not efficient for the design I had in mind, including a

caster wheel, a platform to use the motor to move the arm forward and backwards, and an arm to

safe the mines are a few. Additions were also made after testing, including the metal protrusions

on my wheels, the sled that the back end rests on, the actuator to allow the final step of the


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mountain to be climbed, the height adjustment of for the arm, and the blue padding on the front

top and bottom of the arm to allow a better grip on the mines.

I. Conclusion

In the end, I think I did a fairly good job with my robot. I attempted to build a robust

design, probably sacrificing efficiency in a particular area. With more practice, and a fewmodifications, I think I could have been much more effective. Most importantly, I had a really

good time learning to use the shop and building my robot, and I think I learned a lot about the

design process. Special thanks are in order to Nick, Jamie (TA) and Quentin for helping me a lot

with ideas.

Documents

MENG 185 Final Report