Remote Control Vehicle Report

Final Report

ME250F2014-74

By

Valerie Chen

Andrew Lewis

Nan Li

Andrew Lin

Bo Tian

December 15, 2014

Our RMP was one of two defensive robots in our squad for the M-Ball tournament. Our RMP

needed to be able to push other objects, such as opponent RMPs and the Wolverine. The

purpose of pushing other objects was to effectively disable or at least delay the objectives of an

opponent RMP. Our design was also capable of contributing offensively, by scoring points for

pushing the Wolverine over the hole. Therefore, we needed to design an RMP with high driving

torque and a flat surface to push other objects. Our RMP had a relatively simple yet effective

design. A 1/4” thick aluminum sheet metal part supported by beams and angle stock served as

the flat surface for pushing. A double gearbox with a high (344:1) gear ratio powered to

independent axles, and each axle had three high traction wheels to minimize slipping when

pushing. A 1/16” aluminum sheet metal part was cut to the proper dimensions using the water

jet, and holes for the beam supports, angle stock, gearbox, pillow blocks, and wiring were drilled

using the drill press. This design helped our squad ultimately win the M-Ball tournament.

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TABLE OF CONTENTS

INTRODUCTION……………………………………….……………………………………….. 1

SQUAD STRATEGY……………………………………….……………………………………. 2

Description of Problem……………………………………….…………………………... 2

Stakeholders……………………………………….……………………………………… 2

Domain……………………………………….…………………………………………… 2

Environment……………………………………….……………………………………… 2

Description of Squad Strategy……………………………………….…………………… 3

Functional Decomposition…………..…………..…………..…………..…………..……. 4

RMP Actions in Design Structure Matrix…………..…………..…………..…………….. 4

RMP Actions in Gantt Chart…………..…………..…………..…………..……………… 5

RMP CONCEPTUAL DESIGN…………..…………..…………..…………..………………….. 6

Guardian’s Role in Squad Strategy…………..…………..…………..…………………… 6

Attributes and Requirements Decomposition…………..…………..…………………….. 6

Preliminary RMP Concept 1, Powertrain…...……..…………..…………..……………... 7

Preliminary RMP Concept 2, Chassis……….……….……….……….……….…………. 9

Preliminary RMP Concept 3, Blocking System……….……….……….……….……… 10

Final RMP Concept…………..…………..…………..…………..…………..…………. 11

Solid Model of Concept……….……….……….……….……….……….……………... 12

Description of Concept……….……….……….……….……….……….……………… 12

How RMP Meets Assigned Role…………..…………..…………..…………..………... 12

Aesthetics of RMP…………..…………..…………..…………..……..……..…………. 12

RMP DESIGN EMBODIMENT……….……….……….……….……….……….……….…… 14

Solid Model of Embodiment……….……….……….……….……….……….………… 14

Photos of Actual RMP……….……….……….……….……….……….………………. 14

Description of Embodiment…………..…………..…………..…………..……………... 15

Design Iterations…………..…………..…………..…………..…………..………….…. 15

How Key Dimensions Were Determined…………..…………..…………..………….... 15

Analyses and Tests…………..…………..…………..…………..…………..…………... 15

Aesthetics and Craftsmanship of Embodiment…………..…………..………..………… 16

RMP FABRICATION……….……….……….……….……….……….……….……….……... 17

Bill of Materials (includes material selection justification)……….……….……………. 17

Material Selection Justification.…….……….……….…….……… …….……………... 17

Fabrication Issues…….……….……….………….……….……….…………………….18

RMP VALIDATION AND VERIFICATION…….……….……….………….……….………..19

Alterations to Beam-Chassis and Beam-Wall Connectors…….……….……….………. 19

Alterations to Wall-Chassis Connector…….……….……….………….……….………. 19

Overall RMP Validation…….……….……….………….……….……….…………...... 21

Subsystem Verification…….……….……….………….……….……….……………… 21

STRATEGY VALIDATION AND VERIFICATION…….……….……….…………………... 24

CONCLUSION…….……….……….………….……….……….………….……….……….…. 25

REFERENCES…….……….……….………….……….……….………….……….……….…. 26

APPENDIX A…….……….……….………….……….……….………….……….……….…... 27

APPENDIX B…….……….……….………….……….……….………….……….…………… 36

APPENDIX C…….……….……….………….……….……….………….……….…………… 37

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APPENDIX D…….……….……….………….……….……….……………………………….. 44

APPENDIX E…….……….……….………….……….……….………….……….…………… 47

APPENDIX F (GANTT CHARTS)…………………………………………………………….. 48

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LIST OF FIGURES

Figure 1: The North Campus arena; the only things not pictured…………………………………3

Figure 2: Sketch of Squad Strategy…………………………………………………………….. 3,6

Figure 3: Functional Tree of Squad Strategy……………………………………………………... 4

Figure 4: RMP Actions of Squad Strategy in DSM………………………………………………. 4

Figure 5: RMP Actions of Squad Strategy……………………………………………………….. 5

Figure 6: Three concepts for powertrain design………………………………………………….. 7

Figure 7: Three concepts for chassis design……………………………………………………… 9

Figure 8: Three concepts for blocking system design…………………………………………... 10

Figure 9: Hand sketch 1 of final RMP concept…………………………………………………..11

Figure 10: Hand sketch 2 of final RMP concept…………………………………………………11

Figure 11: Solid model of final RMP concept……….……….……….……….……….……….. 12

Figure 12: Solid model of embodiment……….……….……….……….……….……….……... 14

Figure 13: Solid model of embodiment……….……….……….……….……….……….……... 14

Figure 14: Side view of actual RMP……….……….……….……….……….……….………… 14

Figure 15: Orthogonal view of actual RMP……….……….……….……….……….………….. 14

Figure 16: Beam-Wall Connector utilizes square aluminum tube……….……….……….…….. 20

Figure 17: Small aluminum blocks are not used to attach pushing wall to chassis……………... 20

Figure 18: Angle block connecting pushing wall and chassis provides sufficient support……... 20

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LIST OF TABLES

Table 1: Requirement decomposition and justification…………………………………………... 6

Table 2: Concept #3, with the highest score of 16, was implemented in the robot………………. 8

Table 3: Concept #3, with the highest score of 18, was implemented in the robot………………. 9

Table 4: Concept #3, with the highest score of 12, was implemented in the robot……………... 10

Table 5: RMP speed exceeds system level requirement……….……….……….……….……… 22

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INTRODUCTION

The M-Ball game was created for the ME-250 class and is played by robotic machine players

that have been designed, built and tested by ME-250 students. There are nine squads

participating in the game and each squad consists of four teams. Each team will construct one

robotic machine player (RMP-250). Our squad, with its four RMP-250s, will compete against

other squads in the “M-Ball” competition and try to win each round of the game. To win, we

must score the most points within five minutes in the North Campus arena, which is a table with

fenced edges and a very specific layout. There are three different balls and three different scoring

locations in the arena. There is a central Ball Tower containing normal Ping-Pong balls, red

rubber balls and black rubber balls on tiers of the tower. Black balls are also located on both far

sides of the table. Each squad’s four RMP-250s will start in one corner of the table with the

opposing team starting on the opposite side. The large scoring baskets and scoring holes will be

across from the starting areas, and a smaller scoring basket will be on the corner of each starting

area. Both the types of balls and the scoring locations where the balls are placed will affect the

number of points a team scores. The Wolverine statue, which is initially in the middle of the

table, can also be used to score by moving it on top of an opponent’s scoring hole. In addition,

we receive a 75-point bonus if we manage to maneuver the Wolverine statue so that it

completely covers our opponent’s ball hole.

There are several constraints in the game. One constraint is that the materials provided for

making the RMP-250s are limited, and the squad can only spend at most an extra $200 on parts.

In addition, RMP-250s must fit in a box of dimensions 10” x 12” x 15” high, and can be a

maximum of 15 pounds. Another constraint is that the dimensions of the arena are fixed. The

RMP-250s need to be able to move on the table easily and quickly without falling off the edges

or getting stuck. Finally, none of the RMP-250s are allowed to harm the opposing robots.

Our Squad 7 strategy is composed of four RMP-250s with different roles. The first RMP, known

as R1, or the tower mover, will move the tower toward our scoring hole and drop all the plastic

Ping-Pong balls inside the tower into our scoring hole at one time. The second RMP-250, or R2,

will be the bodyguard of R1 to protect its movement, defend against the opponent, and help

move the tower if necessary. The third RMP-250, R3, will comprise our main offense, and will

get the balls from the top of the tower and then drop them into baskets. The last RMP-250, R4,

will mainly go to block the opponent’s basket as well as act as backup offense (by moving the

black balls beneath our basket into our scoring hole) if necessary.

Team 74 has been tasked with designing and building one of four RMP-250s that will be used to

help Squad 7 win the “M-Ball” competition, specifically to serve as a bodyguard (R2). The

bodyguard’s primary objective is to defend the tower mover and take care of any obstacles that

attempt to prevent the tower mover from getting the Ball Tower over our ball hole. The

bodyguard’s secondary objective is to physically block the opponent’s robots and prevent them

from acquiring balls.

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SQUAD STRATEGY

Description of Problem

Squad 7 is divided into four teams, and each team will construct one robotic machine player

(RMP-250). With its four RMPs, our squad will compete against other squads in the “M-Ball”

competition and try to score the most points within five minutes in the North Campus arena.

There are four ways to score points in the arena:

(1) Deposit balls into the rear basket

(2) Deposit balls into the front basket

(3) Deposit balls into our squad’s scoring hole

(4) Move the Wolverine statue over the opponent’s ball hole.

The squad’s final score is determined by multiplying the weight of the balls in the rear basket by

2, adding this to 1.5 times the weight of the balls in the front basket, and adding the weight of the

balls deposited into our squad’s scoring hole. In addition, we can receive a 75-point bonus if we

manage to maneuver the Wolverine statue so that it completely covers our opponent’s ball hole.

There are several constraints in the game. For instance, the materials provided for making the

RMPs are limited, and the squad can only spend an extra $200 on parts. In addition, RMPs must

fit in a box of dimensions 10” x 12” x 15” high, and can be a maximum of 15 pounds.

Stakeholders

Everyone in the squad is a stakeholder because we are all invested in winning the game.

Domain

The domain of our design is each of the four RMP-250s. They will all have different designs in

order to fulfill their required roles.

Environment

The environment is the North Campus arena, which is a table with fenced edges and a very

specific layout (see Figure 1 on the next page). Besides the starting zones of the two squads,

there are two lower, smaller “front baskets” in each corner of the arena (closest to the starting

zones) and two higher, taller “rear baskets” close to the scoring holes of the two teams. The team

that starts with its four RMP-250s in Starting Zone 1 aims to get balls into Scoring Hole 1 and

Basket 1, and the team that starts in Starting Zone 2 aims to get balls into Scoring Hole 2 and

Basket 2. In addition, there is one hollow Ball Tower filled with lightweight ping-pong balls

centered between the two baskets, with tiers on the tower holding two red balls and two black

balls. There is also a Wolverine statue centered between the two sides of the arena. Finally, there

are eight black balls at the front of the arena, four in front of each team’s Starting Zone, and

eight black balls at the rear of the arena, below each team’s basket.

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Figure 1: The North Campus arena; the only things not pictured are the two shorter baskets in the

two corners closest to the starting zones.

Description of Squad Strategy

Figure 2: Sketch of Squad Strategy

Our selected strategy is composed of four RMP-250s with different roles. The first RMP, known

as R1, will be a tower mover. By moving the tower toward our scoring hole, it will drop all the

plastic Ping-Pong balls inside the tower into our scoring hole. The second RMP, or R2, will be

the bodyguard of R1 to protect its movement, to defend against the opponent, and to help move

the tower if necessary. The third RMP, R3, will comprise our main offense, and will get the balls

from the top of the tower and then drop them into baskets. The last RMP, R4, will mainly go to

block the opponent’s basket as well as act as backup offense (by moving the black balls beneath

our basket into our scoring hole) if necessary.

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Functional Decomposition

Figure 3: Functional Tree of Squad Strategy

RMP Actions in Design Structure Matrix

1 2 3 4 5 6 7 8

R4 moves to Ball Tower and collects high balls 1

R3 blocks opponent baskets/ball hole 2

R1 moves Ball Tower over our scoring hole 3 1

R2 clears obstructions in the path of the Ball Tower 4 1

R4 deposits high balls into basket 5 1

R1 moves Wolverine over opponent’s scoring hole 6 1

R2 clears obstructions in path of Wolverine 7 1

R4 obstructs opponent robots 8 1

Figure 4: RMP Actions of Squad Strategy in DSM

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RMP Actions in Gantt Chart

Figure 5: RMP Actions of Squad Strategy

0:00 1:00 2:00 3:00 4:00 5:00

RMP #1 Move the tower

RMP #1 Adjust tower position

RMP #1 Guard tower

RMP #2 Clear the way

RMP #2 Clear the hole

RMP #2 Guard the tower

RMP #3 Proceed to the target area

RMP #3 Block the basket

RMP #4 Proceed to the target area

RMP #4 Gather first ball and score

RMP #4 Repeat the score process

Time (min:sec)

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RMP CONCEPTUAL DESIGN

Guardian’s Role in Squad Strategy As illustrated in the arena (Figure 2) and the strategy description, our RMP’s role in the squad

strategy will be to be a bodyguard (R2). The bodyguard’s primary objective is to defend the

tower mover, and to take care of any obstacles that attempt to prevent the tower mover from

getting the Ball Tower over our ball hole. The bodyguard’s secondary objective is to physically

block the opponent’s robots and prevent them from acquiring balls.

Figure 2: Sketch of Squad Strategy

Attributes and Requirements Decomposition To fulfill our RMP’s role, we identified and mapped the objectives, attributes, constraints, and

requirements into this chart and analyzed it.

Mission

Requirement

Create an RMP-250 capable of acting as a “bodyguard” that

1. Can push opponent robots out of the way without damaging them

2. Can defend the tower moving robot as it moves the Ball Tower over our

scoring hole.

Originating

Requirements Powertrain

Blocking

system Chassis Electronics

System

Requirements

1. Powerful

2. Easy to

manufacture

3. Simple to

assemble

4.

Lightweight

1. Padded and

nonlethal to

opponent robots

2. Lightweight

but sturdy

3. Large surface

area

4. Mobile

1. Smaller than 10” x

12” x 15” high

2. Large enough to

contain all

components

3. No dangerous

sharp protrusions

4. Wheels have high

traction

1. Simple controls

to drive robot

2. Easy to rapidly

manipulate

blocking system

3. Simple wiring

4. Uses available

power efficiently

Table 1: Requirement decomposition and justification

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Powertrain: First, the powertrain of the RMP must be powerful so that the robot will be able to

effectively push opponent robots out of the way. Second, the powertrain must be easy to

manufacture and simple to assemble so that we can easily fabricate it, test it, and make

alterations as needed. In addition, the powertrain needs to be lightweight so that our RMP can

move and rotate quickly.

Blocking system: First, the blocking system must also have a large surface area so that opponent

robots cannot simply drive around the blocking robot, and it must be mobile to account for a

wide range of potential opponent robots we may encounter. In addition, the blocking system

must be lightweight to move quickly, but sturdy to push opponent robots out of the way without

breaking.

Chassis: First, the chassis of the robot must be smaller than 10” x 12” x 15” high as mandated by

competition rules, but it must be large enough to contain all the needed components. In addition,

this robot cannot feature any dangerous sharp protrusions because they would interfere with its

mobility and also would create a risk of accidentally harming an opponent robot. Finally, the last

requirement of the chassis is that it must have high-traction wheels in order to effectively move

opponent robots out of the way.

Electronics: First, the electronics portion of the robot must have simple controls so that our

robot driver does not need extensive practice with it prior to competition. In addition, the

electronics system must utilize simple wiring to facilitate alterations, and it must utilize the

available power efficiently to minimize space taken up on the robot and the overall weight of the

robot.

Preliminary RMP Concept 1, Powertrain Our RMP must be powerful enough to push obstacles out of the way, and therefore we need a

robust powertrain. We considered implementing several different powertrains and created a

design selection matrix to help us select the best option.

Figure 6: Three concepts for powertrain design; Concept #3 is the one used in the robot.

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Description: We at first designed two wheels sharing one motor (Concept #1) since it was easy

to operate and simple to build. However, we would have greater power if we added a second

motor. So our second concept (Concept #2) had one front wheel and one back wheel assembled

with two independent motors. Then we found that this concept was not able to rotate and needed

to be improved. Finally, we designed our third concept (Concept #3) to have two wheels aligned

horizontally with two independent motors. In this design, when we need to turn our robot, we

can apply a voltage across one motor while the other stays at rest.

Design Selection Matrix: In our design selection matrix (Table 2), we thought that quick

acceleration was the most important so we gave it the maximum weight of three points. The next

most important was flexible rotation (two points) and ease of operation (one point).

Attributes Weight Concept #1 Concept #2 Concept #3

Quick acceleration 3 1 3 3

Flexible rotation 2 2 1 3

Ease of operation 1 3 1 1

Sum 10 12 16

Table 2: Concept #3, with the highest score of 16, was implemented in the robot.

Quick acceleration: Both Concepts #2 and #3 have two motors and maximum acceleration, so we

gave them each three points. We gave #1 only one point because it only has one motor.

Flexible rotation: We gave three points to Concept #3 since its independently controlled wheels

allow it to easily turn and rotate. Concept #1 can turn while moving forward, but cannot rotate on

the spot, so we gave it two points. Finally, Concept #2 received one point because it does not

easily rotate.

Ease of operation: Concept #1 received three points because one motor makes it easy to operate.

We gave one point to Concepts #2 and #3 because both have two independently controlled

motors.

Overall, after analyzing the matrix, we picked Concept #3 as our final powertrain concept.

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Preliminary RMP Concept 2, Chassis The chassis also plays an important function in our ability to perform our assigned role. The

chassis and wheel/castor placement greatly influences the stability of our RMP, and therefore we

considered several different design concepts before selecting the best one using a design

selection matrix.

Figure 7: Three concepts for chassis design; Concept #3 is the one used in the robot.

Description: We at first considered having one front roller and two rear wheels (Concept #1).

We then figured out that if we had two rollers, the front part of our RMP would be more stable.

So we created the second concept (Concept #2), which has two front rollers and two rear wheels.

Finally, we found that if we could move the two rear wheels to the middle and move one roller

from the front to the back (Concept #3), then if an opponent tries to push our RMP from the side,

we will be able to better resist the torque.

Design Selection Matrix: In our design selection matrix (Table 3), we thought that stability

should be most important, so we gave it a maximum weight of three points. The next most

important was ease of rotation (two points) and resistance to getting turned by other robots (one

point).


Stability 3 2 3 3

Ease of rotation 2 2 2 3

Resistance to getting

turned

1 1 2 3

Sum 11 15 18


Stability: Concepts #2 and #3 are more stable since they have four components supporting the

robot body. Hence, Concepts #2 and #3 received three points, while Concept #1 only received

two points.

Ease of rotation: Concept #3 is easier to rotate than Concept #2 and #1 since its two wheels are

positioned in the middle of the robot, closer to its center of mass. Thus, we gave Concept #3

three points, whereas Concepts #1 and #2 only received two points.

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Resistance to getting turned: When an opponent tries to push our RMP from the side, Concept #3

would have the greatest ability to resist rotation because the wheel positioning creates a small

moment arm for the force, and so it received three points. Concept #1 has the smallest ability to

resist rotation because it only has one roller in the front, so it received only one point. Concept

#2 received two points because its ability to resist getting turned is greater than that of Concept

#1 but less than that of Concept #3.

In summary, after analyzing the matrix, we picked Concept #3 as our final chassis concept.

Preliminary RMP Concept 3, Blocking System Because our main role was to block opponent RMPs, we considered various blocking

mechanisms to implement our role. We created a design selection matrix to choose the best

blocking system.

Figure 8: Three concepts for blocking system design; Concept #3 is the one used in the robot.

Description: At first we designed two angled arms on the front to create a large blocking area

(Concept #1). But we then found that this concept may not be able to navigate tight spaces on the

table. Then we designed a trapezoidal body shape that had a narrow front area, which would

enable our RMP to navigate tight spaces (Concept #2). However, the narrow front part of the

trapezoidal body limited the blocking area of our RMP. Since our RMP’s role as a bodyguard

requires sufficient blocking area, we designed the third concept in the shape of a square in order

to strike a balance between a large blocking area and being able to navigate tight spaces

(Concept #3).

Design Selection Matrix: In our design selection matrix (Table 4), we thought that the wide

pushing area was the most important, so we gave it the maximum weight of three points. The

next most important attribute was resistance to rotation (two points) and ability to navigate tight

spaces (one point).


Wide pushing area 3 3 1 2

Resistance to

rotation 2 1 2 2

Ability to navigate

tight spaces 1 0 2.5 2

Sum 11 9.5 12


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Wide pushing area: It’s clear that Concept #1, with the wide blocking arms, has the largest

pushing area, so we gave it three points. Concept #3 received two points for a moderate pushing

area, and Concept #2 got one point for the smallest pushing area.

Resistance to rotation: Since Concept #1 has the longest blocking arms, it also has the longest

moment arms and is therefore the design that would most readily rotate if an opponent pushed it,

so it only received one point in the design selection matrix. Concepts #2 and #3 each received

two points because they have a similar ability to resist rotation.

Ability to navigate tight spaces: Concept #1’s large blocking arms make it almost impossible for

it to navigate tight spaces, so it received 0 points for this category. Concept #2’s trapezoidal

shape has a narrow front, so it’s relatively easier to navigate tight spaces when driving forward.

However, since the tail ends of Concepts #2 and #3 have the same design, Concept #2 does not

have that much more of an advantage over Concept #3. Therefore, Concept #2 only received a

half point more than Concept #3.

Overall, after analyzing the matrix, we selected Concept #3 as our final blocking system design.

Final RMP Concept

Figure 9: Hand sketch 1 of final RMP concept

Figure 10: Hand sketch 2 of final RMP concept

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Solid Model of Concept

Figure 11: Solid model of final RMP concept

Description of Concept The wall at the front of the RMP is used to push obstacles in the arena. It is made out of wood to

provide rigidity and a large surface area. A piece of 1/16” thick aluminum sheet metal is placed

in front of the wood to prevent the wood from flexing during competition. The wall and sheet

metal are bolted to the chassis. Two beams made out of aluminum stock are then connected from

the top of the wall to the end of the chassis to add support to the wall. The Tamiya gearbox with

independent motors powers the two wheels independently, allowing for easy maneuvering and

controlled rotation of the RMP. The wheels have rubber treads for added traction. The drivetrain

assembly (gearbox, drive shafts, and wheels) is placed beneath the center of the chassis.

How RMP Meets Assigned Role Our final design hinges around the RMP’s ability to push other RMPs, the Ball Tower, and the

Wolverine. The large surface area of our front pushing wall and the rigidity of the supporting

beams enables us to effectively perform this role. In addition, high-traction, rubber wheels

provide the necessary grip to withstand the forces exerted by obstacles as we push them. There

are holes in the chassis plate so that the top of the wheels can stick out of the chassis, allowing

the chassis to be lower and therefore lowering the center of gravity, which reduces the possibility

of our RMP tipping over. Finally, the two castors centered at the front and back of the RMP help

stabilize the chassis.

Aesthetics of RMP Our RMP’s overall design, judging from the aesthetics criterion, revolves around the idea of

simplicity. In our design, we make use of the ample space the chassis plate supplies. On the top,

between the beams and wheels, we will attach the control box; much wiring in the middle of the

RMP, which we will leave the rest of the space above the chassis plate to accommodate. The

beams and connectors are also located on the far edges to provide maximum space. We

therefore have the motors, gearbox, and wheel axles below the chassis. Not only does this help

to lower the center of gravity, but it also hides many of the RMP’s components from plain sight

13

to help maintain its simple look. These components are also surrounded by the wheels and

castors to shield them from possible obstacles and obstructions on the arena.

We have thus designed the RMP’s components to be well-spaced to ensure all components

function properly without any interferences. This will fortify the RMP’s reliability and help us

achieve the simplistic design. Our squad’s overall strategy may also benefit from this because

with a simple design, opponents may potentially overlook it analytically and be caught off-guard

if our RMP excels at carrying out its role.

14

RMP DESIGN EMBODIMENT

Solid Model of Embodiment

Figure 12: Solid model of embodiment

Figure 13: Solid model of embodiment

Photos of Actual RMP

Figure 14: Side view of actual RMP Figure 15: Orthogonal view of actual RMP

15

Description of Embodiment

A 1/4” thick aluminum sheet metal part supported by beams and an angle block serve as the flat

surface for pushing. A double gearbox with a high (344:1) gear ratio powers independent axles,

and each axle has three high traction wheels to minimize slipping when pushing. Our chassis is

made out of a 1/16” piece of aluminum sheet metal that was cut to the proper dimensions using

the water jet, and holes for the beam supports, angle stock, gearbox, pillow blocks, and wiring

were drilled using the drill press.

Design Iterations No significant design iterations were needed as a result of our analysis, testing, or scrimmage.

Our RMP performed as expected.

How Key Dimensions Were Determined

The key dimensions of the robot were mainly determined by the size constraint in the rules,

which dictated that our robot had to be smaller than 10” x 12” x 15” high. We therefore designed

our chassis to be approximately 9” x 11” so that it would fit within these constraints. The wheels

on our RMP were custom ordered; we deliberately chose smaller diameter wheels (2-3/8”) to

increase the amount of torque. Other key dimensions were determined by the stock that was

available to us and by our overall goal of designing an RMP that was durable and stable.

Analyses and Tests

Below we have determined the necessary values of key dimensions to use for analysis of our

RMP’s final design to show that the requirements are met. Lengths are directly measured, and

forces along with the coefficient of static friction are estimated with justification for each.

r = 1.5 in = .125 ft

d1 = 3 in = .25 ft

d2 = .5 in = .0417 ft

l1 = l2 = 2.75 in = .229 ft

W = mg = 14 lb — This is a rough estimate. The control box is approximately 1 lb; the chassis

plus wheels, motor, gears, and axles are estimated to weigh approximately 3.5 lb; the front

wall is estimated to weigh 4.5 lb; the two beams are about 2 lb in total; and for added

stability and also to balance the downward moment caused by the front wall, the extra

weights on the back are about 3 lbs. The total weight makes sense as we are aiming to

create a relatively heavy RMP to act as a sturdy wall against other RMPs.

F = 2 lb — This is an approximate average force we expect other RMPs will be able to exert on

our own RMP. We predict that the majority of our opponents will be taking more offensive

types of roles, such as obtaining and scoring the balls, so they will not be mainly designed to

push others. Therefore, we assumed a relatively low value for this force.

FD = 6 lb — This is an approximate force we expect our RMP’s wheels will exert against the

objects it pushes. We took into account our gear ratio, as well as our RMP’s role compared

to other RMPs. Since we determined F to be about 2 lb (as justified before), we are

confident that our RMP will be able to push a maximum of three times that force.

µ = .5 — Looking up the static coefficients of friction for material similar to that of the Ping-

Pong table, we determined that this was the most logical value.

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See Appendix C for calculations on slipping force, tipping force, and the motor and gearbox.

From our analyses, we determined that our vehicle would slip before it tipped and that a gear

ratio of 344:1 should be used if we use the double gearbox to drive our wheels.

Aesthetics and Craftsmanship of Embodiment

The RMP’s aesthetics are almost identical to what we envisioned in our design concept. The

RMP’s design is simplistic with ample space provided by the chassis plate. The middle-back of

the plate is allotted to the control box, and the rest of the middle will be room for the wiring.

The gearbox, motors, and axles are on the underside as planned and have enough room to

function reliably.

We are satisfied with the overall craftsmanship of the RMP. All edges have the correct finishes,

burrs are all removed, and sharp edges are all filed down. The only slight issue we had was with

the tolerances of the holes while installing the beams with their connectors. These were easily

resolved as we changed the holes for the chassis plate connectors to slotted holes, and in the end,

every component installed perfectly in its correct location.

17

RMP FABRICATION

Bill of Materials

Part # Description Material Dimensions Supplier Quantity Price

1 Chassis

baseplate

1/16”

aluminum plate 9”x11”x1/16” Kit 1 -

2

Chassis-

Wall

Connector

1” aluminum

angle block 1”x1”x7” Kit 2 -

3 Metal

pushing wall

1/4” aluminum

plate 1/4”x11”x6” Kit 1 -

4 Wheels Plastic &

Green Rubber

2-3/8” outer

diameter x 0.4”

thick, 1/2” hex

mount

BaneBots 6 $16.50

5

Tamiya

70168

Double

Gearbox Kit

- - Kit 1 -

6 Wheel shafts

3/8” aluminum

rod

0.11” diameter,

2” length Kit 2 -

1/2" aluminum

hex

1/2" diameter,

1.5” length McMaster 2 $1.00

7 1” ball caster - - Crib 2 -

8 Support

Beams

1/2" aluminum

square stock

1/2" x 1/2" x

12” Kit 2 -

9 Pillow

blocks

1” aluminum

angle block 1”x1”x1.5” Kit 2 -

10

Beam-

Chassis

Connectors

3/4" aluminum

tube

3/4" x 3/4" x

3” Kit 2 -

11 Beam-Wall

Connectors

3/4" aluminum

tube

3/4" x 3/4" x

4” Kit 2 -

12 Fasteners

and Washers

1/4”-20 Screws

4-40 Screws - Kit - -

Please see Appendix D for more detailed engineering drawings and manufacturing plans.

Material Selection Justification The majority of our materials were selected directly from the provided kit because it was

cheapest and most convenient. We believed that the components in the kit would be strong

enough to withstand the forces we anticipated our RMP would experience. The wheels were the

only materials that we decided to purchase from an outside manufacturer because we wanted

more traction to be able to effectively push obstacles in the arena. We chose the wheels with the

highest coefficient of friction to be able to meet our objectives.

18

Fabrication Issues One fabrication issue arose when we manufactured the beam connectors. While machining away

the surface of the tube that the beam was going to go through, we took too large a depth of cut.

The chips overheated, and instead of cleanly separating from the part, they became stuck in the

flutes of the end mill. Eventually, this chip build-up blocked the cutting surfaces of the end mill,

which prevented us from cutting away more material. To solve this manufacturing problem, we

cleaned out the flutes of the end mill and reduced our depth of cut.

Another manufacturing issue arose when machining the pillow blocks. We had the blocks in the

mill so we could drill and ream the hole for the bearings to go into. We wanted to clamp the part

tightly in the vice because a big drill bit was going to be drilling into a small part. However, we

did not account for how soft aluminum was and how much force the vice could put on it, and the

part deformed slightly. The free fit bolt holes that had already been drilled were deformed into an

elliptical shape, and we had to re-drill the holes so that they were circular again and the bolts

could fit through.

While we were fabricating the support system for the drivetrain, we used two bearings that were

pressed into two pillow blocks to support the shaft. However, the shafts were too big for the

bearings and we had to sand it down to a proper size so that the shafts could be pressed into the

bearings to support the whole RMP.

19

RMP VALIDATION AND VERIFICATION

The manufacturing and assembly processes generally went accordingly to plan; however, there

were a few important changes that were made.

Alterations to Beam-Chassis and Beam-Wall Connectors Initially, to connect the beam and the chassis, we planned to drill a hole straight through the

beam and chassis and simply fasten them together with a bolt and nut. However, because the

beam sits at an angle relative to the chassis, we realized that this method would be difficult to

execute—we would either have to drill the beam while it was sitting at an angle (which could

cause the drill bit to deflect) or we could drill a hole perpendicular to the beam, in which case the

fastening nut would not sit flush with the chassis.

To eliminate these problems, we devised a fastening method that instead used the 3/4” square

aluminum tube. With this method, the beam sits inside the aluminum tube (the top part of which

has been milled away to make room for the beam) and a hole is drilled through the beam and two

walls of the tube. A fastener is placed through this hole and secured in place with a nut on the

end, thus holding the beam to the connector. A hole is then drilled through two walls of the

square-tube connector and the chassis and a fastener is placed through this hole. This secures the

connector to the chassis. A similar system was used to fasten the beam to the wall (see Figure 16

on next page).

This deviation from the manufacturing plan should improve the amount of force the pushing wall

will be able to withstand because the load is now being carried by two fasteners instead of just

one. It also made our manufacturing easier.

Alterations to Wall-Chassis Connector Originally, we were going to attach the pushing wall to the chassis using two small aluminum

blocks (see Figure 17, on next page). However, after building the pushing wall and considering

the large reaction forces it would experience when pushing other RMPs, the tower, and the

Wolverine, the small aluminum blocks did not seem like enough support. Furthermore, the way

that they only connected to the chassis at one point created a less rigid connection between the

pushing wall and the chassis.

We thus decided to use the angle block and create one long bracket, fastened at two points to the

chassis and two points to the pushing wall, to support the base of the pushing wall (see Figure

18, on next page). The angle block’s two points of fastening to the chassis don’t allow the wall

to move as much as the aluminum blocks. The angle block provides more support than the

blocks by being taller and providing support along most of the length of the pushing wall, instead

of just two points.

Using this fastening method should increase the amount of force the pushing wall will be able to

withstand and overall make our robot more durable.

20

Figure 16: Beam-Wall Connector utilizes square aluminum tube

Figure 17: Small aluminum blocks are not used to attach pushing wall to chassis

Figure 18: Angle block connecting pushing wall and chassis provides sufficient support

21

Overall RMP Validation The scrimmage was the validation process for our whole RMP. It is easy to lose sight of the

intent of the robot during the very detail-oriented manufacturing stage. However, the scrimmage

confirmed that we did, in fact, build the right thing. Our RMP was able to push other RMPs,

effectively getting in their way and delaying or derailing their plans. We pushed opponent RMPs

away while our teammates were busy collecting balls and moving the tower. Our RMP was also

able to push the Wolverine and push other robots into the scoring holes. Our RMP successfully

performed its role as the “Guardian.”

Subsystem Verification

Our verification methods focused on the three main subsystems of our design: the powertrain,

chassis, and blocking/pushing wall.

Powertrain Operational Level Verification

Operational Requirement: Be able to drive forward and rotate.

Quantifiable Requirements: Rotate 360 degrees.

Drive in a straight line.

Drive forward and backward.

Operational Test: Rotate the RMP using the remote control 360 degrees ten times.

Follow a straight line on the floor ten times.

Drive backward and forward ten times.

Test Results: The RMP successfully completed all tests.

System Level Verification

System Level Requirement: Drive an average speed of at least 0.5 feet/second in order to

cross the entire arena in 20 seconds.

Operational Test: Drive the RMP 10 feet five times.

Use a stopwatch to time how long it takes the RMP to drive the

10 ft distance.

Calculate the speed of the run.

Calculate the total average speed by finding the sum of the

average speeds and dividing by 5.

22

Test Results:

Trial Time (seconds) Distance (feet) Speed (feet/second)

1 12.01 10.0 0.8326

2 12.02 10.0 0.8319

3 11.50 10.0 0.8696

4 11.56 10.0 0.8651

5 10.72 10.0 0.9328

Table 5: RMP speed exceeds system level requirement

Based on our tests, the RMP has an average speed of 0.8684

feet/second, which exceeds the system level requirement.

Component Level Verification

Component Level Requirement: The powertrain must be able to withstand approximately half

the weight of the RMP (3 lbs). The casters support the other half

of the load.

Component Level Test: Drive the RMP with all components attached.

Test Results: The powertrain can support the load created by the weight of the

RMP.

Chassis

Operational Level Verification

Operational Requirement: The chassis must be able to hold all components of the RMP.

Operational Test: Measure the chassis dimensions with calipers to ensure that they

match the engineering drawing.

Test Results: The dimensions of the chassis are consistent with the

engineering drawing and the RMP.


System Level Requirement: Assemble all of the components and ensure that they fasten

easily.

Operational Test: Attach the pillow blocks, gearbox, angle block, and beams and

make sure they all easily fit through the holes without

excessively twisting/stretching/stressing any of the components.

Test Results: The RMP assembles easily.

23


Component Level Requirement: The bolts must be able to freely fit through the holes.

Component Level Test: Check that the chassis holes are not threaded.

Measure the diameters of the chassis holes to ensure that they

are free fit holes for the bolt going through them.

Make sure bolts are not too long (the part of the bolt

sticking out should not be more than 1.5 times its diameter).

Test Results: All bolts are properly installed and fit through the chassis.

Pushing/Blocking Wall

Operational Level Verification

Operational Requirement: The pushing/blocking wall must able to push other RMPs.

Operational Test: Attempt to push another RMP.

Test Results: Our RMP was able to push multiple other RMPs.


System Level Requirement: Have a wall that is rigidly attached to the chassis by beams and

an angle block support.

Operational Test: Place ballast on top of the wall and make sure that there is no

play at any of the fastening points or throughout the beams and

angle block. Be sure that there is no bending in the wall.

Test Results: The wall is rigidly attached to the rest of the RMP.


Component Level Requirement: The RMP must be able to generate a driving torque of at least

𝑇𝐷 = 𝜇𝑁𝑟 = 1 ∗ 8 lb ∗2.375 in

2

12in

ft

= 0.79 ft ∙ lbf. The value for 𝜇,

the coefficient of friction between the wheels and the table, was

set equal to 1 because engineeringtoolbox.com listed the

coefficient of friction between rubber and plastic as 1. The value

for 𝑁, the normal force, was set equal to 8 lb because 8 lb is the

mean weight of the RMPs whose estimated weights we had

access to (RMPs from our squad and others). The value for 𝑟,

the radius of the wheels, was set equal to the diameter of the

wheels (2.375 in), divided by 2 to obtain the radius, and then

divided by 12 to convert inches into feet.

Component Level Test: Push an 8 lb RMP.

Test Results: The RMP successfully pushed an 8 lb RMP.

24

STRATEGY VALIDATION AND VERIFICATION

Our squad performed very well in both the scrimmages and the tournament. We only lost one

match in the scrimmage, and we won the tournament. All of our RMPs were functional and

capable of performing the roles originally assigned to them. In the scrimmage match that we

lost, we lost because an opponent RMP scored several black balls in the 1.5-multiplier basket at

the beginning of the game while we were focusing on implementing our tower-moving strategy.

After this loss, we made a point to not only focus on executing our own squad strategy, but also

to be mindful of the actions of our opponents.

After the scrimmage, all four teams decided to practice their driving, which paid off during

competition. The combination of the spring-loaded and non-spring-loaded joysticks on the

controller made driving the RMP tricky, so a good amount of practice was required. Our robots

were all functional after the scrimmage; the only major tweaks teams made involved eliminating

wheel slip by ensuring setscrews were tight and creating more grip by adding wheels. We knew

that all of our RMPs were capable of doing what was required of them, and if we could make

changes that would allow us to perform our tasks quicker and with more control, we would be in

good shape.

Our small changes paid off. The scrimmage allowed us to see how an M-Ball game develops,

and therefore we were able to perform better in the tournament. Our RMP prevented several

opponent RMPs from performing their goals, while the other RMPs in our squad helped push the

tower and score balls in baskets. Ironically, we won the final game the way we lost our

scrimmage game, as one of our teams scored several black balls in the 1.5-multiplier basket at

the very beginning, proving that we did study our scrimmage results and make changes.

25

CONCLUSION

The setup of the M-Ball game allows students to go in many different directions with the design

of their robot. The M-Ball game is complex, as there are multiple types of balls with different

point values, three different places to deposit balls, two large objects (the Wolverine and Ball

Tower) and eight RMPs in the arena at the same time. Therefore, each team had different ideas

on how to score the highest number of points, which led to very different designs across the

squads.

The complexity of the game required us to think like engineers and spend a large amount of time

discussing and strategizing before actually beginning to model and manufacture the RMP. It was

oftentimes hard to agree on a design concept because there were a lot of variables and unknowns

associated with the game. This required us to think critically and analyze various outcomes

without actually being able to test or experiment.

The manufacturing of the RMP made us appreciate how much work goes into manufacturing

parts and mechanisms. Making sure holes align, that shafts slide through bearings without

bending, and that the appropriate tolerances are chosen are all important steps that cannot be

neglected. It made us realize just how crucial it is to prepare properly by making good drawings

and having a good concept before actually building.

Our robot was fairly simplistic. However, because of this, we were able to build a very effective

robot that had all of its subsystems working properly. At the same time, building a more

complex robot would have perhaps allowed us to learn about more mechanical systems,

materials, and manufacturing processes. For example, we did not use a rack and pinion or

acrylic, and we never used a laser cutter, so we did not learn as much about these common

design elements. If we were to do it again, we would add another motorized function, so that we

could learn more about a different type of gearbox and transmission and gain more machining

and manufacturing experience.

We are proud and satisfied that we were able to take a concept and then use CAD and stock

materials to make a unique robot. Being able to see the entire process, from squad strategy

generation to the actual tournament, was an incredibly valuable experience, and one that we will

certainly be able to apply later as engineers.

26

REFERENCES

Lecture Slides of ME 250 Instructors Panos Papalambros and Mike Umbriac

27

APPENDIX A

The Ideation Process

We used the Classic SE Pyramid Model to aid us in generating our preliminary strategies. We

first identified our mission requirement, which was to win the game by obtaining the greatest

number of points. We then broke up this mission requirement into a series of originating

requirements, or things we could do in order to win the game. There were five of these

originating requirements:

(1) Obstruct opponent robots

(2) Cover opponent’s ball hole with Wolverine

(3) Move Ball Tower over our team’s scoring hole

(4) Deposit balls into our basket(s)

(5) Deposit balls into our scoring hole.

After we identified our originating requirements, we brainstormed the system requirements, or

the steps we would need to take to achieve each of the originating requirements, which are

organized in Figure 2 below.

Requirement decomposition of squad strategy

We utilized the system requirements to generate roles for the four RMP-250s and aimed to

complete as many of the originating requirements as possible. Two preliminary strategies that

Team 74 generated using this requirement decomposition are detailed in the following section.

28

Preliminary Strategies

Team Strategy 1

Sketch:

Sketch of Team Strategy 1

Description:

R1 in the diagram above pushes the Wolverine on top of the opponent’s scoring hole and then

proceeds to block/prevent the opposing team from obtaining balls. R2 collects the red and black

balls on the tiers of the tower and deposits them into our scoring basket. R3 retrieves the light

ping-pong balls from the bottom of the tower and pushes them into our scoring hole. R4 starts

near the metal bracket at the back of our starting zone and is in charge of depositing the black

balls under the basket and near our starting zone into our scoring hole.

Strengths:

1. We have versatile scoring. This strategy involves all RMP-250s scoring through different

methods (in the ball hole, in the basket, and with the Wolverine) and using all ball types.

2. All RMP-250s are independent. Each RMP-250 goes about its own tasks and is not

reliant on the performance (or lack thereof) of the other RMP-250s.

3. All RMP-250s are specialized. Each RMP-250 has a very specific set of tasks, and

therefore can be designed accordingly to maximize each RMP’s potential.

Weaknesses:

1. It will possibly be difficult to design or manufacture some of the mechanisms required to

achieve these tasks.

2. A lot of the scoring in this strategy relies on access to the scoring hole. If the other team

blocks or covers up the scoring hole, our team could end up missing out on a lot of

points.

29

Put Wolverine over opponent's

scoring hole

Beat opponent to Wolverine

Start match as close to Wolverine

as possible

Give RMP a lot of low end torque

Steer/control Wolverine

Push Wolverine from behind with

enough torque

Have an arm with "claws" on either side of Wolverine

to guide it

3. All RMP-250s are specialized. While this is a strength, it could also be a weakness

should a system failure occur, because the RMP-250 would be rendered nearly useless if

it cannot perform its only task.

Risks and Methods of Addressing Risks:

1. One risk is that we could design an RMP-250 that is hard or impossible to manufacture

during the building stage. This risk can be avoided by ensuring we have a thorough

knowledge of the available tools, resources, kit, and budget in order to design

appropriately.

2. Another risk is that the opposing team may block our scoring hole. If this occurs or seems

like a likely possibility, the RMP-250s in charge of scoring in the scoring hole (R3 and

R4) should work together to prevent the obstruction from being set up or removing it if it

is already in place.

3. A third risk is that any one of the RMP-250s is at risk for a system failure. To mitigate

this risk, the RMPs should have a secondary/backup mechanism in addition to the

primary features required to complete their task so that the RMP can still contribute to

scoring/blocking the opponent even if it fails in its primary duty.

Functional Trees:

RMP #1 Functional Tree

Functional Tree 1 of Team Strategy 1

30

Score black and red balls in the basket

Retrieve black and red balls from atop

the ball tower

Swipe balls off of perch on ball tower

and into a receptacle on the

RMP

Carry balls from ball tower to basket

Carry balls in a secure receptacle

Put balls in the baskets

Use a projectile to launch balls into

baskets

Position RMP in front of basket at appropriate angle

Lift balls out of receptacle

Use a claw to lift balls

Score blue and yellow balls in the scoring hole

Collect balls out of the bottom of the ball tower

Use a claw mechanism that opens and closes in

order to grab balls

Transport balls from the ball tower to the hole

Use two arms to direct the balls towards the

scoring hole

Deposit balls into the scoring hole

Score low placed black balls in the

scoring hole

Retrieve black balls from both

ends of the arena

Carry balls to scoring hole

Use a claw to grip the ball

Make RMP easily

maneuverable

Deposit balls into the scoring

hole

Release grip on the claw to drop

the ball







31

RMP Actions:

RMP Actions of Team Strategy 1

Outcomes:

1. We successfully move the Wolverine over the opponent’s scoring hole and it remains

there for the duration of the game. All ball retrieval efforts are successful.

Squad 7’s predicted score: 450

Opponent’s predicted score: 300

Probability: Average to high

This outcome relies on the successful maneuvering of the Wolverine over the opponent’s

scoring hole. Assuming everything our squad has planned is successful and all RMPs can

continue to collect balls for the duration of the game, this score is possible.

2. One or more RMPs fails at their primary duty.



Probability: Low

If one of our RMPs fails, this would result in a large loss of points because it would be

unable to collect balls for the remainder of the game. However, if this were to occur, the

RMP could focus exclusively on defense, resulting in a low score for the opponent as

well.

3. Squad 7 operates highly efficiently; the other team experiences a failure.

Predicted score: 500


0:00 1:00 2:00 3:00 4:00 5:00

Drive towards black balls at the back of the arenaGrab a black ball

Carry the black ball to the scoring holeDrop the ball in the scoring hole

Continue to place black balls in the scoring holeDrive towards ball tower

Grab yellow and blue balls out from the bottom of the towerTransport balls to scoring hole

Deposit yellow and blue balls in the scoring holeContinue to put yellow and blue balls in the scoring hole

Drive towards ball towerPosition RMP in front of black balls on tower

Lift arm up to the height of the black ballSwipe the black ball down and into the basket

Drive to the tall basketUse arm to lift ball up the height of the basket

Drop the ball into the basketCollect the remaining black balls

Lift arm up to the height of the red ballsPlace the red balls in the baskets using the same process

Drive towards wolverinePosition RMP behind wolverine

Use arms to grab and guide wolverineDrive towards oppenent's scoring hole

Position wolverine over scoring holeDefend wolverine/obstuct opponent's paths

Time (min:sec)

32

Probability: Low

This score would only occur if our team operates very efficiently with little to no

resistance from the opposing team. In addition, if the other team experiences a failure of

one or more of their RMPs (getting stuck, falling off the table, etc.), this would allow us

to achieve a very high score by collecting more than 50% of the available balls.

Team Strategy 2

Sketch:

Sketch of Team Strategy 2

Description:

This strategy focuses on having an even balance between the offensive and the defensive. RMPs

1 and 2 (R1 and R2) will be positioned at the top left corner of the starting area as they have the

priority roles. R1 will first head over to the Wolverine statue and push it onto the opponent’s

scoring hole. It will spend the remainder of the game protecting the Wolverine and interfering

with the opponent’s potentially scoring via basket. R2 will head straight for the tower and gather

both the red balls and the ping-pong balls. It will score in either the basket or the hole (with the

basket and elevated balls being top priority), depending on the situation. Since this is the main

method of scoring, R3 will follow closely behind R2 to protect it and make sure opposing robots

do not interfere. R3 will then move into the area near the scoring hole and basket to defend both

R2 and R4. R4 will start at the bottom, close to the black balls. It will deposit the black balls into

the scoring hole and proceed to gather and score the black balls on the opposite side as well.

Strengths:

1. One strength of this strategy is its balance between scoring and defending. If one robot of

either role fails, there will be a backup for each of them to carry on the competition.

2. A second strength is that with two defensive robots instead of one, it will be more

feasible to counter interferences from the enemy team.

33

3. A third strength is that all robots are independent from one another; one robot does not

become unproductive if any other robot fails.

Weaknesses:

1. A weakness of this strategy is that R2 will be difficult to manufacture because of its need

to gather all types of balls from the tower.

2. This strategy has only two offensive robots rather than three, and therefore has less

versatile scoring than other methods like Team Strategy 1.

3. All robots are specialized, so losing any of them would mean its corresponding role

would be lost as well.

Risks and Methods of Addressing Risks:

1. A robot may get stuck in the scoring hole (R4 is at the greatest risk for this). To counter

this, we should to ensure that our robots (R4 in particular) have wheels that are large

enough to maintain traction on any side of the hole in order to escape the hole if they ever

fall in. We also need to practice driving the vehicles to acquire a good feel for the nature

of each robot’s movements.

2. R2 and R4 may fail to score properly. This can be mitigated by sufficient testing and

revisions to their designs.

3. The enemy’s team strategy will likely consist of hindering our performance, so effective

use of scrimmages is necessary to understand and take into account the possible obstacles

we will encounter.

Functional Tree:

Functional Tree of Team Strategy 2

34

RMP Actions:

RMP Actions of Team Strategy 2

Outcomes:

1. The red ball is placed in the tall basket, all eight black balls are deposited into the scoring

hole, and the Wolverine statue stays on top of the enemy’s scoring hole for the duration

of the game. Our defense has successfully interfered with the enemy.



Probability: Low

This outcome has a low probability of occurring because it predicts that the red ball is

placed in the basket and the Wolverine statue is in place over the opponent’s scoring hole

for the entire game. The Wolverine statue will most likely be a target for the opponent as

well.

2. The red ball is placed in the tall basket, all eight black balls are placed in the scoring hole,

about 15 ping-pong balls are also deposited into the scoring hole, but the Wolverine

statue is not in place. Our defense somewhat successfully interferes with the enemy.



Probability: Medium-High

This outcome has a medium/high probability of occurring because it is likely that both

teams will go after the Wolverine statue and it will end up somewhere in the middle of

the table, not covering either scoring hole.

3. The red ball is not placed in the tall basket, all eight black balls are placed in the scoring

hole, only 10 ping-pong balls are deposited into the scoring hole, and the Wolverine

statue is not in place. Our defense provides little pressure to the opponent’s offense.



Probability: Medium-Low

Assuming that we follow through with all our plans to mitigate our risks during the

competition, this outcome should have a medium to low probability of occurring.

0:00 1:00 2:00 3:00 4:00 5:00

Push the statue using a U-shaped base

Extend long arms/barrier upwards to deflect balls

Drive in the way of enemy robots

Drive to tower

Collect red ball

Drive to basket to dump ball

Collect black balls and score in basket or hole

Drive alongside Robot 2 up to the scoring area

Block approaching robots

Collect nearest black balls and score

Drive up to hole and drop balls in

Time (min:sec)

35

Diagram of final squad strategy

36

APPENDIX B

Extra Final Design Picture

Hand sketch of the pushing plate of our final RMP concept

37

APPENDIX C

Vehicle Tipping Calculations

Consider the following free body diagrams of the back wheels and front rollers of our vehicle

which we will be analyzing:

We will assume these wheels to be massless because their weight is negligible in comparison to

the weight of the other components. From the free body diagrams, we can produce the following

equation of force balance in the x-direction:

∑ 𝐹𝑥 = 0 = 𝐹𝐷 − 𝐹2 Eq. (1)

For the y-direction:

∑ 𝐹𝑦𝐴 = 0 = 𝑁2 − 𝑓2 Eq. (2)

∑ 𝐹𝑦𝐵 = 0 = 𝑁1 − 𝑓1 Eq. (3)

We can also create a moment balance equation for Figure 23:

∑ 𝑀 = 0 = 𝐹𝐷𝑟 − 𝑇𝐷 Eq. (4)

N2

F2

TD

f2

FD

N1

f1

r

FBD of the back wheels. FBD of the front rollers.

38

Now, consider the following free body diagram of the body of the vehicle:

We will create a force balance equation once again for the x-direction:

∑ 𝐹𝑥 = 0 = 𝐹2 − 𝐹 Eq. (5)

For the y-direction:

∑ 𝐹𝑦 = 0 = 𝑓1 + 𝑓2 − 𝑚𝑔 Eq. (6)

The moment balance around the center of gravity:

∑ 𝑀 = 0 = 𝐹𝑑1 + 𝐹2𝑑2 + 𝑓1𝑙1 − 𝑓2𝑙2 Eq. (7)

Rearranging Eq. (1) and Eq. (5):

𝐹𝐷 = 𝐹2

𝐹2 = 𝐹

Thus:

𝐹 = 𝐹2 = 𝐹𝐷 Eq. (8)

From Eq. (8), we can write Eq. (7) in terms of FD and simplify:

0 = 𝐹𝐷(𝑑1 + 𝑑2) + 𝑓1𝑙1 − 𝑓2𝑙2 Eq. (9)

Using Eq. (6) and Eq. (9), we can find f1:

𝑓1 + 𝑓2 − 𝑚𝑔 = 0

𝑓2 = 𝑚𝑔 − 𝑓1

l2 l1

d2

d1 f2 f1

F2

F

mg

FBD of the vehicle body.

39

𝐹𝐷(𝑑1 + 𝑑2) + 𝑓1𝑙1 − (𝑚𝑔 − 𝑓1)𝑙2 = 0

𝐹𝐷(𝑑1 + 𝑑2) + 𝑓1𝑙1 − 𝑚𝑔𝑙2 + 𝑓1𝑙2 = 0

𝐹𝐷(𝑑1 + 𝑑2) − 𝑚𝑔𝑙2 = −𝑓1(𝑙1 + 𝑙2)

𝑓1 =−𝐹𝐷(𝑑1+𝑑2)+𝑚𝑔𝑙2

𝑙1+𝑙2 Eq. (10)

From Eq. (3), Eq. (10) becomes…

𝑁1 =𝑚𝑔𝑙2 − 𝐹𝐷(𝑑1 + 𝑑2)

𝑙1 + 𝑙2

In the same manner, we can use Eq. (2), (6), and (9) to find N2:

𝑁2 =𝑚𝑔𝑙1 + 𝐹𝐷(𝑑1 + 𝑑2)

𝑙1 + 𝑙2

In the case of tipping, there would be no normal force on the front wheel. This means 𝑁1 < 0.

Our equation for N1 then becomes…

𝑚𝑔𝑙2 − 𝐹𝐷(𝑑1 + 𝑑2) < 0

𝐹𝐷 >𝑚𝑔𝑙2

𝑑1 + 𝑑2= 𝐹𝑡𝑖𝑝

This is our tipping force.

Using the values of the key dimensions we had previously determined to plug into this equation,

we obtain the following:

𝐹𝑡𝑖𝑝 =14 ∗ .229

. 25 + .0417= 10.991 𝑙𝑏

Vehicle Slipping Calculations

If the vehicle slips, we can say that the driving force exceeds friction. This means 𝐹𝐷 > 𝜇𝑁2.

Our equation for N2 then becomes…

𝐹𝐷 >𝜇𝑚𝑔𝑙1

𝑙1 + 𝑙2 − 𝜇(𝑑1 + 𝑑2)= 𝐹𝑠𝑙𝑖𝑝

This is our slipping force.

Plugging in our values into this equation:

𝐹𝑠𝑙𝑖𝑝 =. 5 ∗ 14 ∗ .229

. 229 + .229 − .5(.25 + .0417)= 5.135 𝑙𝑏

Tipping vs. Slipping Conclusion Since our Ftip > Fslip, this indicates that our vehicle would slip before it could tip over.

40

Motor/Gearbox Calculations Consider Figure 26, in which a basic model of our robot design is subjected to a force F from a

robot we are theoretically attempting to push. TD represents the torque created by our

motor/gearbox combination acting on the rear wheel of our robot, while r represents the radius of

the front wheel. Keep in mind that this diagram represents a rough approximation of our robot,

and that it assumes the robot has four wheels, while in reality, our robot has two wheels and two

casters. The black and white circle on the robot represents its center of mass.

Basic model of robot being subjected to force F from opponent robot.

According to this diagram, in order for our robot to be able to move to the right, the driving

torque of the back wheel must equal the resistant torque created by the opponent robot, which is

equal to F*r. Therefore, we can use Equation 11 to calculate the required driving torque, TD:

𝑇𝐷 = 𝑓𝑠𝐹𝑟 Eq. (11)

In Equation 11, fs represents the factor of safety, which is assumed to be 1.5 for this analysis. F is

estimated to be approximately 2 lbs, due to some experimental testing with a force gauge in the

lab. The radius of the wheel, r, is measured to be 1.5 in.

𝑇𝐷 = 1.5(2 lbs)(0.125 ft) = 0.375 ft ∙ lbf

Once we know the required driving torque, the next step is to select the motor that we would like

to use in our robot. The analysis that follows compares the performance of the three motor-

gearbox options: the Pololu 130-sized DC motors and double gearbox, the Mabuchi RC-260SA-

2295 and planetary gearbox, and the 99:1 Metal Gearmotor 25Dx54L mm HP.

Double Gearbox:

Because we would like to have two independently controlled wheels, the most convenient choice

would be to use the Tamiya 70168 Double Gearbox, which has a stall torque (TS0) of

0.002286 ft·lbf and a no-load speed of 11500 rpm for one motor. The dual gearbox makes use of

two motors, and therefore our true stall torque would be 0.002286*2 = 0.004572 ft·lbf.

After calculating our stall torque, the next step should be to scale the stall torque and the no-load

speed to the input voltage; however because the data sheet of the motor-gear system assumed a

nominal voltage of 6 V (which is the same as the voltage we plan to run it at), no scaling is

required.

41

Assuming the motor operates at maximum efficiency, we can calculate the required torque (Tr)

by using Equation 12:

𝑇𝑟 = 0.2𝛾𝑇𝑠0 Eq. (12)

In Equation 12, γ represents the efficiency of the gearbox, which is assumed to be 0.25 for this

analysis. This assumption is based off of the knowledge that γ is typically 5-30% for an entire

gearbox. Based on the loads we expect our gearbox to experience, we believe our gearbox will

be running near its maximum efficiency of 0.30, somewhere between 70 and 90% of its no-load

speed.

𝑇𝑟 = 0.2(0.25)(0.004572 ft · lbf) = 0.000229 ft · lbf

After calculating the required torque, we can calculate the required gear ratio (Mr) using

Equation 13:

𝑀𝑟 =𝑇𝐷

𝑇𝑟 Eq. (13)

𝑀𝑟 =0.375 ft · lbf

0.000229 ft · lbf= 1640

Unfortunately, the largest gear ratio the dual gearbox can obtain is 344, so this is what our robot

will have to use. To ensure that this lower gear ratio will still be sufficient to move our robot

though, we need to check to make sure that the stall torque of our motor-gear system (with the

344:1 gear ratio) will be greater than the required driving torque, TD. The stall torque (TS) of any

motor-gear system is calculated using Equation 14:

𝑇𝑆 = 𝛾𝑀𝑇𝑆0 Eq. (14)

𝑇𝑆 = (0.25)(344)(0.004572 ft · lbf) = 0.393 ft · lbf

This is greater than the required driving torque (TD = 0.375 ft·lbf), so a gear ratio of 344:1 should

be sufficient for our needs.

Planetary Gearbox:

If we were to use two planetary gearboxes instead of the double gearbox, we would use a similar

analysis format to determine the optimal gear ratio. The motor used with the planetary gearbox,

the Mabuchi RC-260SA-2295, has a stall torque (TS0) of 0.009588 ft·lbf and a no-load speed of

10200 rpm for one motor. We would utilize two independently controlled motors to ensure our

robot has the ability to turn, so our stall torque would actually be 0.009588*2 = 0.01918 ft·lbf.

After calculating our stall torque, the next step is to scale the stall torque and no-load speed to

the input voltage. The given values on the data sheet assume an input voltage of 4.5 V, but we

plan to run the system at 6 V. Using Equations 15 and 16, we can scale the stall torque and no-

load speed to obtain the true values:

𝑇𝑆2 =𝑉2

𝑉1𝑇𝑆1 Eq. (15)

42

𝑇𝑆0 =6 V

4.5 V(0.01918 ft · lbf) = 0.025568 ft · lbf

𝑛02 =𝑉2

𝑉1𝑛01 Eq. (16)

𝑛0 =6 V

4.5 V(10200 rpm) = 13600 rpm

Assuming the motors operate at maximum efficiency, we can calculate the required torque (Tr)

by using Equation 12, from above:

𝑇𝑟 = 0.2𝛾𝑇𝑠0 = 0.2(0.25)(0.025568 ft · lbf) = 0.001278 ft · lbf

After calculating the required torque, we can calculate the required gear ratio (Mr) using

Equation 13:

𝑀𝑟 =𝑇𝐷

𝑇𝑟=

0.375 ft · lbf

0.001278 ft · lbf= 293.4

The closest available gear ratio for the planetary gearbox would be 400:1. The last step in the

gearbox analysis is to ensure that this gear ratio (400:1) will be sufficient to move our robot (the

stall torque of the motor-gear system is greater than the required driving torque). Using Equation

14, from above, we can calculate the stall torque:

𝑇𝑆 = 𝛾𝑀𝑇𝑆0 = (0.25)(400)(0.025568 ft · lbf) = 2.5568 ft · lbf

This is greater than the required driving torque (TD = 0.375 ft·lbf), so a gear ratio of 400:1 should

be sufficient for our needs.

When deciding on a motor/gearbox combination to use, we also need to be mindful of space and

resource constraints.

Testing Plans In order to ensure that our RMP performs as optimally as possible and fulfills its roles, we have

devised three essential functions that can be quantitatively evaluated: pushing ability, speed, and

ability to resist external forces.

Pushing Ability One of the key functions is the ability to push objects and other RMPs from the front. This is by

far its most vital task since our robot was designated by our team to act as a wall against our

opponents.

How to Test: To test how well our robot performs this function, we can measure the amount of

force it exerts when driving forward at its maximum speed. The most efficient way to measure

the amount of force exerted by our robot when driving forward is to attach a spring scale to the

back of the RMP and have it continuously drive forward until it stalls or starts slipping.

43

Testing Equipment: We will have to find a spring scale that has a measuring range specifically

encompassing the force the RMP is able to exert, and this will be the only device we will need

for the testing process.

Potential Design Changes: If we require the RMP to exert a greater force when pushing from the

front, we could adjust the gear ratio of the gearbox to exert an even greater torque if it is not

already on the highest ratio, or we could find an even stronger motor to replace the current one.

We could also attach additional parts to the bottom of the RMP that make contact with the table

surface in order to provide even more friction.

Speed

The second essential function is a combination of the RMP’s acceleration and its maximum

velocity that it can drive at. Since our role is mainly defensive, this characteristic is not as

important as the others, but still needs to be addressed as we want the RMP to be able to reach its

designated positions and catch other robots as quickly as possible.

How to Test: We will have one measured distance be equivalent to that of the length of our

RMP’s starting position to the area next to the tower. This distance will mainly be used to

observe how quickly the RMP can accelerate and get to that position; we will time it to see how

long it takes. A second measured distance will start farther ahead of the RMP to ensure that it

can reach its maximum velocity before it enters that distance. We will divide that distance by the

time it takes to run through it to find the velocity.

Testing Equipment: All we need is a stopwatch and certain measured distances.

Potential Design Changes: If we desire a greater acceleration or maximum velocity, we can

lower the gear ratio to increase the top speed, find an even stronger motor, or reduce the weight

of the RMP.

Ability to Withstand External Forces

The last function is the ability to withstand other RMPs potentially pushing our RMP from its

corners and edges. This is an important issue to address as our RMP is essentially rendered

useless in its ability to wall others if they can push through us.

How to Test: We can test this by using the same method we will use for testing the first function.

That it is, we will attach a spring scale to each corner of the RMP and tug at the spring scale

slowly until the RMP starts to shift or rotate.

Testing Equipment: We would need a spring scale that measures in the range of how much force

it would take to rotate our RMP.

Potential Design Changes: If we want the RMP to resist moments from its sides even more

effectively, we can again attach more parts to its bottom side near its front and back edges to

provide more friction, or reconfigure its wheel and roller positions.

44

APPENDIX D

Manufacturing Plan 1

Part Number: ME250-001 Revision Date: 10/22/2014

Part Name: Chassis

Team Name: Team 74, Guardian

Raw Material Stock: 1/4” Aluminum Plate from Kit

Step

# Process Description Machine Fixtures Tools

Speed

(RPM)

1

Use height gauge to mark out

dimensions of plate (9” x 11”)

and use shear to cut plate

slightly larger than these

dimensions

Shear

Height

Gauge,

Surface Plate

2 Break edges of part by hand File

3

Clamp plate in vice, ensuring it

is adequately supported with

2+ parallels, machine both

edges that are hanging off vice

to make them parallel

Mill Vice

Parallels, 1/2

inch 2-flute

endmill,

collet

840

4

Unclamp plate, break edges,

rotate part 90°, reclamp part

and machine the other two

edges to make them parallel

Mill Vice

File,

parallels, 1/2

inch 2-flute

endmill,

collet

840

5

Remove plate from vice and

break all edges. File corners

especially well

File

6 Reclamp part, find datum lines

for X and Y. Mill Vice

Edge finder,

drill chuck 1000

7 Center drill and drill 0.2010 in

holes Mill Vice

Center drill,

drill chuck,

#7 drill bit

1200

8 Center drill and drill pilot holes

for large pockets Mill Vice

Center drill,

drill chuck,

1/2” drill bit

600

9 Use endmill to machine large

pockets Mill Vice

½ inch 2-

flute endmill,

collet

840

10 Remove part from mill; break

and deburr edges File

45



Part Name: Wooden wall


Raw Material Stock: 1/4” Baltic Birch Plywood from Kit

Step


Speed

(RPM)

1

Use Vertical Band Saw

to cut off a 10.2’’ * 5’’

piece of Baltic Birch

Plywood

Band Saw Wood holder

500

2

Mill one end of part to

provide a fully

machined surface.

Mill Vice End mill 800

2

Refine the edges with

end mill and cut it down

to 4.75’’ * 10.00’’

Mill Vice End mill 800

3 Zero from one corner by

finding all the edges Mill Vice Edge finder

4

Move to (1.50, 1.45) in

and (8.50, 1.45) in. Then

center drill and drill two

0.2010 in holes

Mill Vice

Center drill,

drill chuck,

#7 drill bit

800

5

Move to (0.25, 4.75) in

and (9.75, 4.75) in. Then

center drill and drill two

0.2010 in holes

Mill Vice

Center drill,

drill chuck,

#7 drill bit

800

46



Part Name: Beam


Raw Material Stock: 1/2” Aluminum Square Stock from Kit

Step


Speed

(RPM)

1

Use Vertical Band Saw

to cut off a 11.3’’ long

piece of 1/2” Aluminum

Square Stock

Band Saw Wood holder 800

2 End mill the stock to the

exact 11.28’’ length Mill Vice

1/2 inch 2-

flute end mill 840

3

From one end A, mark

an angle of 74.5 degrees

on stock. Start from the

other side and mark the

stock at 9.34’’ away

from where the angle of

74.5 intersects the edge

Marker

4

Connect the end B with

C and remove the extra

part with end mill

Mill Vice 1/2 inch 2-

flute end mill 840

5 End mill to refine the

surfaces Mill Vice

1/2 inch 2-

flute end mill 840

6

Measure all angles and

edges. Mill part if

necessary to make sure

they correspond to the

expected value.

Mill Vice 1/2 inch 2-

flute end mill 840

47

APPENDIX E

Component Redesign: Chassis Plate The chassis plate of our RMP could be improved by making it out of the acrylic plate instead of

aluminum sheet metal.

Problems with Current Design

We used the 1/16” aluminum sheet metal as the chassis plate. We used the water jet to get it

down to size, to curve the corners, and create the large holes for the wheels. We then drill

pressed all free fit bolt holes to allow the angle block, beams, pillow blocks, and gearbox to

attach.

We overestimated the stiffness of the 1/16” aluminum sheet metal. Our RMP places a lot of force

on the sheet metal. The control box and beams create downward force at the back of the chassis,

and the angle block and pushing wall create downward force at the front of the chassis. These

loading conditions make the chassis bend. These downward forces are only counteracted at the

center by the weight of the gearbox, axles, and pillow blocks, which weigh significantly less and

are thus not enough to prevent the chassis from bending.

The issues created by the bending of the chassis include difficulty ensuring that the rollers and

wheels are all level, the pushing wall being closer to the ground than it should be, and less grip

being created at the rubber wheels at the center (thus causing some wheel spin/slip at high wheel

speeds). These defects amalgamate to hinder our ability to effectively control the RMP.

New Requirements and Justification

Making our chassis out of the acrylic plate instead of the aluminum sheet metal would be a

design improvement in the future. However, there would be new requirements, namely a

different manufacturing process from the one we used for producing the aluminum chassis plate.

The acrylic would have to be cut using the laser cutter, and the outer dimensions and wheel holes

would remain the same. However, the position of the bolt holes for the beams, angle block,

pillow blocks, and gearbox would have to be adjusted. Some of the holes on our chassis right

now are close (<0.25”) to the edges of the chassis. This would be a risky design with acrylic,

because it could easily crack. Therefore, all of the holes would have to be moved inward, which

would require a lot of new dimensioning. For example, the pillow blocks would have to be

smaller in order to be placed further inside the chassis, the beams would have to be more

centered as opposed to on the outer edges of the chassis, and the angle block holes would have to

be pushed further inward. However, the acrylic would not compromise the overall functionality

and goals of the RMP. It would simply call for some re-dimensioning in order to create a more

rigid chassis plate.

48

APPENDIX F (GANTT CHARTS)

Team 74 Predicted Timeline of Events as of Milestone 1

Note: All projects are worked on by all team members.

8/31 9/7 9/14 9/21 9/28 10/5 10/12 10/19 10/26 11/2 11/9 11/16 11/23 11/30 12/7 12/14

Strategy Selection

Strategy Report Due

Robot Design

Individual Member Design Brainstorm

Team 74 Meeting and Design Preliminary Finalization

Squad 7 Meeting and Design Edits

Team 74 Meeting and Design Alteration and Finalization

Design Presentations (Milestone 2 Part 1)

Generate Drawings

Design Report Due (Milestone 2 Part 2)

Robot Build

Chassis Construction

Attachments Construction

Manufacturing Plans Complete (Milestone 2.5)

Powertrain Construction

Electrical Wiring

Testing and Alterations

Validation Testing

Validation and Verification Report (Milestone 3)

Design Expo

Final Report Due

49



8/31 9/7 9/14 9/21 9/28 10/5 10/12 10/19 10/26 11/2 11/9 11/16 11/23 11/30 12/7 12/14

Strategy Selection

Strategy Report Due

Robot Design






Generate Drawings


Robot Build





Electrical Wiring


Validation Testing


Design Expo

Final Report Due

50



8/31 9/7 9/14 9/21 9/28 10/5 10/12 10/19 10/26 11/2 11/9 11/16 11/23 11/30 12/7 12/14

Strategy Selection

Strategy Report Due

Robot Design






Generate Drawings


Robot Build





Electrical Wiring


Validation Testing


Design Expo

Final Report Due

51

Team 74 Predicted Timeline of Events as of Final Report


8/31 9/7 9/14 9/21 9/28 10/5 10/12 10/19 10/26 11/2 11/9 11/16 11/23 11/30 12/7 12/14

Strategy Selection

Strategy Report Due

Robot Design






Generate Drawings


Robot Build





Electrical Wiring


Validation Testing


Design Expo

Final Report Due

Remote Control Vehicle Report

Documents