Team 1836: Milken Knights Engineering Recourse 2016

8/18/2019 Team 1836: Milken Knights Engineering Recourse 2016

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Team 1836:

Milken Knights

2016 Engineering Resource


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This document was created with the intent of helping other teams

fully understand our team culture, design process, and robot. We have

gotten inspiration and guidance from dozens of other teams and we

wanted to create an open source platform to share what we have

learned. We publish several other resources for teams on our website

including a blog, game test, FLL resources and Chairman’s resources.

This year these documents were used by over 500 teams. That is 1 out

of every 6 teams in FRC. We track this with a pop up on our website

asking people what team they are on. Please ask us questions! We

love helping other teams. And, let us know if there is something we

can do to help your team!

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Team 1836: Milken Knights


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Table of Contents

Systems 4

Drivetrain 4

Intake 7

Electronics 10

Catapult 11

Iteration Cycles 15

Improvements 16

Cost Accounting Worksheet 27

(CAW)

Contact 28

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Systems

Drivetrain

This year’s drive train is an improved version of the West Coast-style drivetrain that we

have been improving on for the past five years. It can traverse all of the driving

obstacles, park on the Batter, and accurately turn. We prototyped three different

drivetrains; a standard West Coast Drive design, an adjustable West Coast Drive

design, and a four wheeled suspension.

Wheels

The drivetrain is an eight wheel West Coast drive with 200mm (7.67 inch) inch

pneumatic wheels. Different amounts of wheels and types were tested, including six

wheel drives, 6 inch pneumatic wheels, and plastic Skyway wheels. This combination of

wheel size, amount, and type was found to most easily traverse the defenses.

Center to center

While past drivetrains have used sliding bearing blocks to tension the drive chains, this

year’s robot has set wheel center-to-center distances of 8.055 inches. By having set

center-to-center distances, we drastically simplified the previously complex drive rails

and bearing blocks, eliminating many hours of manufacturing time.

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Chain

Three of the wheels on each side of the robot are driven using chain by the main

gearboxes. While many teams use #35 chain, like previous years, this year’s drivetrain

uses #25 chain to maximize the weight available for other parts of the robot. Drive

chains are installed by stretching the chain over the drive sprockets to the point that

they appear to be too tight. The next step is to “wear in” the drivetrain for 20 minutes.

While the chains are initially over tensioned, by the end of the run-in period they are

perfectly tensioned.

Bearing Blocks

The bearing blocks are custom designed and machined. We used a technique

commonly referred to as “drop center” to mount our bearing blocks at differents heights.

The hole of the outer bearing blocks are offset upwards by ¼ inch, which allows only

four of the eight wheels to touch the ground at any time. This reduces the drivetrains

effective wheelbase, which allows it to turn smoothly.

Shifting and Gearing

Each side of the drivetrain is driven by a modified 2 CIM Ball Shifter gearbox, geared for

16 fps(feet per second) in high gear, and 7 fps in low gear. The high gear was

specifically chosen as a balance of speed and acceleration to traverse this year’s field

quickly. The low gear is used to push defensive robots and park on the Batter.

Sensors

The drivetrain uses US Digital’s S4T360 encoders in each gearbox for position and

velocity sensing and a NavX IMU for heading. Closed loop, velocity PID, is used on

every control loop as the base layer that maintains consistent autonomous and

teleoperated performance. By “closing the loop”, feedback from the encoders ensures

that wheel velocity is consistent no matter battery or field conditions. On top of that is

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layered position PID and turn PID to drive straight and turn accurately during

autonomous.

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Intake

The intake is a motorized arm that can be raised and lowered in under a second to acquire

balls. It can also be used to cross the Cheval de Frise. Because the intake serves so many

purposes, our team went through an extra iteration and design work to ensure that the intake is

extremely robust. In particular, iteration to a chained gearbox and specific software and

mechanical failure modes has prevented in match failures. However, in the event of a worse

case scenario, the intake arm hard stops against the bumpers, allowing the robot to continue to

pick-up balls. If our intake does not work we can no longer shoot or low goal so we took extra

precautions to ensure it would work.

Chain

Because the intake accelerates quickly, large amounts of force are placed on the arm

gearbox. An initial prototype intake used a gear final stage, however the final stage

pinion sheared. The next iteration used a new gearbox with the final reduction stage

changed to #25 chain, which is far more robust. One issue with chain is that it stretches.

We utilized a sliding tensioning sprocket to keep the chain tight, eliminating backlash.

This allows us to move our intake with significantly more accuracy and precision. The

chain is easily installed and tensioned through this method and can be replaced in a five

minute match Timeout.

Fastening

Brass pins are used to geometrically locate the sprocket to our intake arm frame, and

then screws hold the entire assembly together. As a result, the intake assembly is

extremely rigid and strong, ensuring that the intake performs consistently and robustly

throughout the season.

Gearing

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The intake rollers are powered by a Bag Motor on a 7:1 Vex Versaplanetary gearbox.

This results in a 10 fps surface speed, quick enough for a ball to be acquired the

moment it touches the front intake roller.

Funnel

On the intake, there are two HDPE (High Density PolyEthylene) strips funneling balls

through the bumper. We tested other materials and found that this slippery surface was

optimal. The full width intake provides a large sweet spot for drivers, easily acquiring

balls regardless of ball position.

Los Angeles Regional Upgrade

We were behind where we had anticipated being on stop build day so we made the

decision to bag the drivetrain and catapult and bring everything else in our 30lb

allowance. Because of this decision we had to basically assemble our robot there. Our

30lb allowance included all of our electronics, wheels, and intake. We came to this

decision because we didn't want to bag anything that wouldn’t be ready or up to par with

the products that we produce. Thursday at the LA regional was a long first day in the

pits. Before competition we had made a detailed plan of what order we were going to

assemble our robot. We prioritized our electronics first before we started to do anything

else. Once we got our electronics on and all of that was adequately tested we got the

wheels on and made sure that all of our modifications worked. Once that was fully

finished, we decided to add the intake.

After the Los Angeles Regional

After the Los Angeles Regional, we made many changes to our practice robot which will

be implemented at the Orange County Regional. After the LA regional we realised that

to be a top tier team, we needed to add or upgrade a few things. We acknowledged that

we needed to use our catapult during matches. In shop, while doing testing, our catapult

broke in half, which meant that we needed to re-machine and design it to be lighter and

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more precise. We made the catapult slightly longer and lighter, by adding 3 holes that

decrease in size while going down the arm. We also realized that we needed to

redesign a new ball clamp for our robot because the existing ball clamp prototype added

too much weight to our catapult and negatively affected our shot. We are redesigning

the clamp and have a few new ideas. One of the existing ideas for a new ball clamp is

to have two actuating cylinders, 1 on each side of our drive train, that will actuate out to

hold the ball in place, and actuate back in right before we take the shot. The team is

also considering a passive solution that will allow the ball to bounce around but not fall

out.

Sensors/Programing

The intake arm position is controlled via a PID loop using feedback from an S4D

encoder on the final gearbox

stage. The intake encoder starts

the match against a hard stop,

which is the stowed, “zero”

position. In case of encoder slip

or robot blackout during the

match, the intake arm can be

slowly driven up and back into

the hardstop, rezeroing the arm

position. In the down position,

the control loop is voltage

limited in order to prevent

premature breakage from impacts with defensive robots and field obstacles. Finally, the

intake and catapult are coordinated to prevent the drivers from accidentally colliding the

mechanisms.

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Electronics

Speed Controllers

The robot uses Talon SRX motor controllers, located on one of the electronics panels of

the robot. Twelve talons are on the right electronics panel in total, four of which power

the drive gearboxes, one of which powers the intake gearbox, and one of which powers

the catapult. Though not all speed controllers are being used at the moment, the team is

prepared for the case of more mechanisms being added to the robot. Having extra

talons pre-wired also allows us to easily switch in case of motor failures.

Battery Mount

To mount our battery this year, we used a group of four 1x1 tubes and a hook and loop

fastener strap. The tubes, riveted to the bellypan, form a tight fit around the battery, and

the strap holds it down. Together, they form a secure battery box that prevents the

battery from becoming dislodged.

Connectors

Every electronic connection on the robot is crimped instead of soldered. Crimped

connections are more reliably and quickly made than soldered connections. High

voltage, power runs, are connected with Anderson Powerpoles. These connectors can

transmit up to 45 amps of current, are colored to show polarity, and can quickly be

disconnected. For signal wires, PWM connectors are used, which have a male and

female side. A female connector on each wire plugs into male side on the RoboRIO.

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instead to let our prototypes make our choices for us. The catapult’s accuracy and

simplicity ultimately made the decision for us.

Cam

A cam is a rotating piece that is used in a mechanical linkage to transform rotational

energy into linear energy. The snail dropcam was originally used in timekeeping devices

to shift between days at exactly midnight. The void created by the snail shell or comma

like geometry creates the firing effect. We decided to use this technique to actuate our

catapult for several reasons. Consistency and repeatability has been a huge design

consideration and our current iteration is only capable of one shot in order to prioritize

these outcomes. Tuning of this mechanism happens outside of the actuation with the

adjustment of spring tensioning and launch angle. By keeping the firing mechanism

constant, it allows us to keep

consistency on our shot throughout

the tuning process, isolating the firing

from other variables. This mechanism

has proven to be tremendously

reliable and repeatable. Our

prototype was hastily made out of

wood and used tape as spacers and

yet was still capable of a 95% shot

accuracy from 17 feet.

Sensors/Programing

The catapult utilizes both an encoder for position and velocity sensing and a hall effect

for zeroing the encoder. The zeroing process starts with a velocity PID loop to spin the

cam at a constant rotational velocity, regardless of the current position of the catapult.

Once the hall effect triggers the robot to zero the cam, a position PID loop takes over. It

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feeds into the velocity PID loop, moving the cam to the reloaded position. When the

driver triggers a shot, the position loop moves the cam 360 degrees, and the process

starts over. The layered PID loops and zeroing processes ensures that the catapult

performs consistently in all conditions.

Hardstop

The hardstop for the catapult was created using sailing line. We tested various lengths

to optimize the ball’s release point.

Gearing

The gear box on the catapult was custom designed. We used a gear ratio of 273.32:1due to its high torque and fast reload time. Our reload time is approximately half a

second which allows us to quickly retract into a position to fit under the low bar defense.

Forces/Springs

In order to launch the catapult, we decided to use springs. The process of choosing the

correct springs was lengthy.

We started with surgicaltubing on our prototype robot.

We calculated how much

force the surgical tubing

applied. From there, we tried

out various combinations of

springs with the surgical

tubing as a guide. Wecalculated the work done by the springs, and used this to pick which exact spring we

wanted. We ended up using two springs with 38 pounds of force each.

Trajectory

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Adjusting the hard stop in conjunction with the spring force allows any trajectory to be

achieved. The catapult’s trajectory was tuned to create the biggest sweet spot possible

from the 14 ft range, which is the distance from the middle of the outer works. In fact,

the chosen trajectory will score anywhere from 7 to 17 feet away. Additionally, the high

release point makes it difficult for a full height defender to block the shot without getting

a penalty.

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Iteration Cycles

This year we have implemented a high iteration, fast prototyping process. We have a

saying on our team “fail fast and fail often.” Learning what doesn’t work helps us getcloser to finding out what does. We have made over 30 iterations and prototypes

throughout this season. This allows us to improve on our designs through testing, not

theory. We had a really difficult time last year making design decisions as a team. Our

solution to that is prototyping everything and allowing the mechanisms to make the

decision for us. This is a huge step for our team because it allows us to focus less on

making the perfect decision, and more on improving based on actual data. We have a

term we have coined “MVP” (Minimum Viable Product). This prevents us from getting

carried away and helps us keep our designs simple and elegant.

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Improvements

Scrum

As a part of improving our team, we have adopted the Scrum method. Scrum is a way

of creating a team approach to problem solving and innovation. Scrum keeps our

leadership on track to make sure that we are accomplishing all of the goals we set.

Using this method, our leadership created a spreadsheet where the team could keep

track of all ongoing progress. The spreadsheet includes a brief description of the

project, what has been completed, what needs to be completed, and the percent

completed.

Performance > Appearance

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After much discussion the leadership team unanimously decided to prioritize

performance over appearance. We have powder coated our robots before competition

every year which took approximately 4 days. Our bare metal and unpainted wood may

be less aesthetically appealing but it allows us to put our resources on other areas. After

the competition season we will powdercoat our robot, leaving us with the same end

product and more time during build season.

Decreased Tapping

This off season a great deal of reflection took place as we thoroughly evaluated every

aspect of our manufacturing process. During last year’s build season we used a tap

wrench to thread over 100 holes. This process was extremely time consuming. The

alternative our team decided on for this year is using a bolt and lock nut but requires

extra space and access holes. Putting a little more time into our designs ultimately

saved us manufacturing time.

Battery Cart

In the offseason, the team decided to build a

better battery management solution. In order tohave a fresh battery for every match, with spares

for alliance partners, the team brings 12 batteries

to competition. Along with these batteries, the

team must also bring 4 chargers. As a result,

packing batteries and their chargers, alone

weighing over 200 lbs, was a time consuming

process. The team decided to combine all this equipment into a single battery cart toease the packing process. This was also a good pre season project to prepare students

for build season and gain experience working with baltic birch.

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The resulting battery cart design had a couple of goals. Firstly, it needed to be easy to

manufacture with the team’s in-shop resources, yet still robust. This was done by using

a largely wood, puzzle-like structure, with a few metal parts used as frame members.

The battery cart also needed to effectively store all the equipment, while being easy to

roll around and fit in the pit. The design is short enough to fit under our pit tables, yet

extremely compact.

Battery Cart Reflection

It was a bit tight to assemble, in part due to some manufacturing issues. In the future

the dimensions of the pockets/holes should be increased to make assembly easier.

The nuts like to twist in their spots, so making the nut slots thinner and more rectangular

could prevent this.

Moving the nuts closer or using longer screws and extending the screw clearance would

allow for the screws' interface with the nuts to occur earlier

Right now, the SB50 battery connectors are locked in place, so it is impossible to add

charger banks and adjust the SB50 connectors without disassembling the cart. This

could be fixed by tapping or using rivet nuts in place of the nut and bolt that holds the

SB50 in place. Drilling a hole in the shelf would allow the SB50 bolt to be accessible.

The hole drilled for the power strip should be added into the CAD. Putting a plastic

piece in the hole would prevent the power strip cord from wearing.

Adding an inset handle into the design could be helpful for optimum transportation, just

in case it needs to be placed flush.

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The material left in the pocket is extremely thin. In the future, making it .1" thick , if not

.15", would be better.

The design should be modified to avoid having to disconnect SB50 connectors from the

chargers (via the fuse holders). 3 fuses broke in this process.

There isn't a lot of space for wires, especially ones with large plugs, and so the cart

must be assembled in a very careful process. Leaving more space for wires without

significantly increasing the cart height could be improved.

Leaving a cutout in the top piece would make it is easier to see the charger lights.

The cart is extremely rigid... maybe too rigid even. The biggest time sink was the bottom

2x1 added for rigidity, so there could be alternative options here.

There may have been issues with radii being exactly .125". The next step is looking into

this problem to see if making the radii .13" would help.

Locking casters would probably be a better choice, as it takes a good bit of force to

insert the battery connector

We could probably use less fasteners on the L battery backstop

There should be a better plan for painting/staining going into the assembly process

All in all, the team is extremely happy with how this project turned out and we enjoyed

testing it full time this year.

Pit Checklist

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To improve our consistency preparing for matches we created a checklist that pit crew

would implement before and after every match. We also use this list to select and train

pit crew and run a series of time trials. We have set up our pit in our shop and practice

to prepare for competition.

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Wood

Wood has a negative stigma in FIRST and is improperly associated with poor design.

Before this season we had almost never used wood. Wood has the major benefit of

machining approximately four times faster aluminum and in some cases, even faster.

Last year our intricate lattice structure belly pan design took 8 hours to machine out of

⅛” aluminum. In comparison, this year’s wood belly pan took only 15 minutes.

One common complaint about wood is the reduced strength. We are using grade B/BB

Baltic birch, significantly stronger than average, Home Depot plywood. 6061 aluminum

has an ultimate tensile strength of 45 ksi ( kilopound per square inch) while baltic birch

has an ultimate tensile strength of 10 ksi. 6061 aluminum has a modulus of elasticity of

10,000 ksi while comparatively baltic birch has a modulus of elasticity of 2,000 ksi. This

data appears to show that Aluminum is much stronger than baltic birch but when you

adjust for density they have the same ultimate tensile strength of 16.7 ksi. They also

have a similar modulus of elasticity when adjusted for density with aluminum being 3703

ksi and baltic birch being 3333 ksi. Instead of making plates out of 1/8 in 6061 aluminum

we now use a 6 mm (0.236 in) sheet of baltic birch. Plates that would have been made

out of ¼ in aluminum are now made from sheets of 12 mm (.472 in) baltic birch. These

baltic birch plates are approximately twice as thick as the aluminum equivalent which

was not always feasible on the robot due to the tight packaging constraints. The void free

core is more uniform than other plywoods and allows for a stable crossband lamination.

Our prototypes were completely made of baltic birch plates. As the design evolved

through the iterative design process we have switched some plates to metal. The belly

pan, upper structure support plates, electronics panels, intake plate, and catapult bucket

arm are all remaining as baltic birch for the final robot.

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Preseason

Training Document

A challenge in the past has been deciding how to effectively prepare new

members. This offseason, our team captains compiled a list of every skill

necessary to participate fully on our FRC team. We compiled these tasks into 3

different categories: green, yellow, and red. Green corresponds to a “beginner

task”, yellow for “intermediate”, and red for “expert”. This system allowed us to

track all team members’ progress, not only ensuring that each team member was

proficient in every possible skill, but also that each and every team member can

point at a part of the robot and confidently say: “I made that.” This training

method is being used by other FRC teams and is even being used as part of a

curriculum that is being developed for students in China.

The first and most important section of our Training Document is Safety and

Cleaning. Students must have this entire section complete before participating in

any activities in the room. This section includes general safety for using all of the

machines in shop (lathe, mill, and router), battery safety and spill clean up, and

other general shop cleanliness items such as sweeping and knowing the place

for each tool.

The next section of the Training Document is the Machining and Mechanical

section. This section lets our students be prepared to use any tool in our shop.

The training starts with simple tools like hand drills and deburring tools all the

way up to being able to operate our big machines.

Other sections in our Document include the Electrical, Pneumatics, and

Programming sections. In these parts of the document, students learn how

decode status lights, connect pneumatic fittings, and even how the FRC field

works. In this section a student could also learn the basics of programming

starting with understanding PID and getting all the way up to motion profiles.

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The last section of our document is the CAD and Design section. In this part of

the document students start off by learning the basics of CAD. They learn how to

navigate Solidworks and use all of the functions like sketch and extrude. After

learning to CAD, students move on to design. This year we had the pleasure of

viewing a design process presentation from Adam Heard where he took us

through all the different steps to designing a robot. This combined with the

different concepts in our Training Document helped our students be ready to

design a robot.

Practice Build Days

This year we have decided to take a much more aggressive approach to build season

by prototyping all possible mechanisms for the 2016 game during the first week of build

season. After we have built prototypes, we can discuss game strategy and make more

informed decisions on what our robot should do.

To practice this prototype heavy approach the legendary Adam Heard of team 973

joined us for three Sundays this fall to help us develop our prototyping abilities. We

thought of these days a practice build season work days. Working with Adam on these

projects was an incredible opportunity for our students and really helped us get ready

for an action packed build season full of prototyping and iteration.

On the first of three build season practice prototyping workshops, we had over 25

students in attendance and the day was an incredible success. We finished an arm and

an elevator prototype and both had running motors. This was probably one of our most

productive build days ever and was a great sign of things to come.

On the second build day we recreating Team 254’s 2014 robot. We used our router to

quickly create all of the necessary parts out of wood and worked and improving our

assembly speed. This day also helped us improve our understanding of how fly wheel

shooters work and created a good base for us when we tested them during build

season.

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On the final of our three practice build days we created our own game similar to the

2006 FRC game to give our team a challenge that had not been completed yet. This

day was the ultimate preparation for build season. We had to CAD, machine, assemble,

and test a robot in one day. This was a great learning experience for build season and

how to work efficiently under time pressure.

Scouting

Improvements

Match scouting was designed this year to be simple and easy for scouters to record

data. In doing this we decided to ignore boulder data as it often can be difficult to see

who scored and if the balls went in. We also wanted to combine quantitative and

qualitative data. Last year we created an app and used tablets but because of the

issues that came up due to the inherent complexity of this simple we decided to test a

paper scouting system. Every team has one sheet that is reused for all of their matches.

A runner brings these sheets to the coach before each match to allow the drive team to

prepare. The most important part of pit match scouting is taking a picture of other

teams. This helps us remember what they look like and look closer at them during our

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down several times during build season this year partially because they were not

maintained and set up as well as they could have been.

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Cost Accounting Worksheet

(CAW)

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Contact

Web

MilkenKnights.com

“Team 1836: The MilkenKnights”

@milkenknights

Milken Community Schools

15800 Zeldins’ Way

Los Angeles, California

90049

(310) 440-3500 x3436

Mentors

Al Noel Sansolis (Robotics Manager) [email protected]

Mark Mascadri (Robotics Coordinator) [email protected]

Roger Kassebaum (Director, MAST) [email protected]

Tanner Ragland (Director of Robotics) [email protected]

Team CaptainsMichael Bick [email protected]

Miranda Milner [email protected]

Austin Shalit [email protected]

Daniel Spar [email protected]

Team Members

Please contact all other team members through our contact form at

milkenknights.com/contact.

Documents

Team 1836: Milken Knights Engineering Recourse 2016