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ME 250 DESIGN AND MANUFACTURING I
Fall 2015
Robot Machine Player (RMP) 250
Team #54
ME 250 Section #5 Team #4
Team Members
Henry Ellis
Elbert Han
Henry Lewis
Taylor Martell
Nirmal Patel
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Table of Contents
1. ABTRACT (1 point)…………………………………………………………………………...4
2. INTRODUCTION (1 point)…....................................................................................................4
3. PROTOTYPE DESIGN (25 points)……………………………………………………………6
3.1. Strategy and Zone Strategy (2 points)………………………………………………..6
3.2. Functional Requirements, Specifications, and Target Values (3 points)…………......7
3.3. Design Concepts and Subsystems (4 points) …………………………………….…..8
3.4. Analysis (10 points)…………………………………………………………………12
3.5. Final Design and CAD Model (6 points)……………………………………………19
4. PROTOTYPE MANUFACTURING (6 points)………………………………………………26
4.1. Manufacturing Process (4 points)………………………………………………...…26
4.2. Bill of Materials (2 points)……………………………………………………...…...27
5. PROTOTYPE TESTING (8 points)………………………………………………..…………30
5.1. Preliminary Test (3 points)……………………………………………………….....30
5.2. Scrimmage Results and Redesign Based on Scrimmage (3 points)……………..….33
5.3. Discussion of Competition Results (2 points)………………………………...…….34
6. DISCUSSION AND RECOMMENDATIONS (5 points)………………………………........35
6.1. Project Summary (2 points)…………………………………………………………35
6.2. Recommendation for Mass Production (2 points)………………………………..…36
6.3. Future Project Idea (1 points)……………………………………………………….37
7. REFERENCES ……………………………………………………………………………….37
8. ACKNOWLEDGEMENTS…………………………………………………………………...37
APPENDICES………………………………………………………………………………...…39
A. Preliminary design concept SKETCHES……………………………………………………..39
A.1. Preliminary Design Concept Sketch 1…………………………………………...…39
A.2. Preliminary Design Concept Sketch 2……………………………………………...39
A.3. Preliminary Design Concept Sketch 3………………………………………….…..40
B. Dimensioned Drawings and manufacturing plans (4 points)…………………………….…...40
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B.1. Dimensioned Drawings of Individual Parts……………………………….……….40
B.2. Manufacturing plans………………………………………………………….……40
C. PURCHASED AND TRADED ITEMS……………………………………………………...41
C.1 Purchased parts………………………………………………………………………41
C.2. Traded parts (inter-squad)…………………………………………………………..42
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1. ABSTRACT (1 point)
At the beginning of this semester, our team was challenged with building a Remotely Manipulated
Player (RMP) that could intake all the blocks in zone 2, travel through a sea of ping pong balls,
pass cubes over an 11 inch wall, and receive cubes passed into zone 2. After better defining the
above tasks into functional requirements, we designed and built a RMP by dividing it into frame,
drivetrain, bucket, and intake subsystems using manufacturing methods ranging from
thermoforming to laser cutting. After running a series of tests on the RMP that we designed, we
determined some critical alterations needed to ensure our RMP functioned as well as possible. In
the days leading up to the competition and in a performance review the day before competition,
our RMP performed satisfactorily, but unforeseen troubles prevented us from performing as well
as expected during the match. While we are happy with our RMP design and our execution of it,
the level of complexity of our RMP made it exceedingly difficult to fabricate in the compressed
timeline of the semester and created too many failure modes to permit reliable long term operation
without much more testing and refining of the design.
2. INTRODUCTION (1 points)
Problem statement:
We were assigned to design and manufacture a RMP that can participate in the Michigan Ninja
Relay.
Background of Michigan Ninja Relay:
The Michigan Ninja Relay takes place on the table shown in Figures 1 and 2 below. The objective
of the game is to score as many points as possible within the time limit of 3 minutes. There are
four teams within each lab section that make up a squad, and each team within the squad are
assigned a different zone of the table. The RMP's all work together by passing cubes from their
zone into the next zone, or into the GOAL basket in the case of zone four. There are initially six
cubes in zone one, five cubes in zone two, four cubes in zone three, and three cubes in zone four.
The scoring is determined by the starting and ending positions of the cubes, based on the following
equation:
where and are the initial and final zone location of the cubes. Table 1 on the next page lists
all possible cases of the initial and final Cube locations and the corresponding scores.
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Table 1: Scoring table
Initial
zone
1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4
Final
zone
1 2 3 4 G 1 2 3 4 G 1 2 3 4 G 1 2 3 4 G
score
0 1 3 5 7 0 0 1 3 5 0 0 0 1 3 0 0 0 0 1
Figure 1: A top view of the table showing all four zones, the yellow boundaries between
them, and the starting positions of the RMP's and cubes within each zone.
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Figure 2: An isometric view of the table, where the obstacles of each zone are easier to
visualize.
3. PROTOTYPE DESIGN (25 points)
A prototype is a model that is built using equipment in order to analyze before scaling upwards.
The model depicts the subsystems that will be made for the future RMP. The model additionally,
should open the eyes of the group to potential design failures when scaling up occurs.
3.1. Strategy and Zone Strategy (2 points)
Our squad agreed that each RMP will prioritize their own cubes before receiving cubes from the
prior zone. Once cubes from the prior zone are successfully transported, these cubes take priority.
This strategy pertains to particularly Zones 1, 2, and 3. It does not pertain to Zone 4 because the
first thing RMP4 will do is move the blocks to make a clear path to the goal. Our squad also
decided to pass the cubes directly over the wall to the next RMP instead of going through the holes.
This strategy was selected after a lab discussion as we realized that collaborating in this manner
would be most efficient in regards to time. A big advantage of this strategy is that no RMP is ever
just waiting around for another team to deliver their cubes. We considered having RMP 2 and
RMP 3 to just wait around for the cubes from zone 1, but realized that it would be time inefficient.
Going over the wall instead of through the wall also has a lot of advantages because it does not
require as much precision, and is easier to ensure a direct pass to the next RMP.
Our team was assigned Zone 2 (see Figure 3). Our strategy involves first picking up all 5 of our
zone 2 cubes at once. Once they are collected, our RMP will descend from the ledge and travel
along a diagonal near the wall that separates zone 1 and zone 2 because it is the shortest possible
distance to the center of the barrier between our zone and zone 3. Our RMP will transfer all five
zone 2 cubes over the wall to zone 3 first. Then, it will move to a position along the zone 1 and 2
barrier where it will receive zone 1’s cubes. The RMP will then transfer the zone 1 cubes to zone
3.
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We decided on this strategy because once we descend into the ping-pong balls, we don’t want to
have to go back onto the ledge. Getting back on the ledge would be a huge stability concern and
would make picking up the cubes from our own zone much more difficult. We also thought that
traveling in close proximity to the wall is the most time efficient and provides extra stability in the
sea of ping pong balls.
Figure 3. This is a screenshot of our zone. The numbers indicated represent the following
locations of our RMP: (1.) Origin of the RMP (2.) Pickup location of zone 2 cubes. (3.)
Cube transport location to RMP3. (4.) Cube receiving location from RMP1. (5.) Second
cube transport location to RMP3.
3.2. Functional Requirements, Specifications, and Target Values (3 points)
Our first functional requirement is to be able to collect all 5 zone 2 cubes at once. This is an
important requirement because we want to be able to pick up all of our blocks at once without
having to ascend the ledge again. To achieve this, we must have a bucket base of at least 4.5 in2
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We arrived at this target value because the cubes will be stacked with two in front and three behind
per competition specifications, and each cube is 1.5 inches wide. Our second functional
requirement is to be able to receive a maximum of all 6 cubes from zone 1. This is important for
efficiency, and aligns with zone 1's strategy. We must have 13.5 in2
of floor space in order to
receive all 6 cubes of 1.5 inches long each.
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Another functional requirement is to have the ability to function after driving off of the ledge. If
the RMP cannot overcome this first obstacle, there is no chance of accomplishing the rest of our
tasks. Our target value was simply a low center of gravity concentrated more towards the back of
the RMP. The reasoning behind a center of gravity towards the back is if the center of gravity is
over the front wheel when going off of the ledge, the RMP will tip. However, if the center of
gravity is in the back as the RMP goes over the ledge, the RMP won't tip. Furthermore, it is
essential that our RMP can travel through the ping pong balls. We decided that bigger wheels is
the best way to achieve this functional requirement. We calculated the necessary radius of the
wheels to clear the ping pong balls based on how high off of the ground the frame must be raised
in order to clear the known diameter of the ping pong balls. The result was wheels with a radius
of 2.16 inches would give us a clearance of .07 inches. This is enough to travel over the ping-pong
balls as well as give us clearance between the frame and the edge. Finally, we decided we wanted
our RMP to be able to travel the distance from the ledge to the drop off point to zone three
(1.3599m) in 15 seconds. It is very important to be able to make this transition relatively quickly
because we must be back in time to receive the blocks from zone 1, and 15 seconds is 1/12 of the
total time given. Zone three must have time to then transfer the blocks to zone four, and zone four
needs time to score the blocks in the goal. Since this calculation does not take into account potential
hindrance of the ping-pong balls, 15 seconds allows room for potential error.
3.3. Design Concepts and Subsystems (4 points)
We were considering three very different initial design concepts. The first design concept (see
Figure A.1 in the appendix) had three sets of wheels, and could flip on its side as a way to descend
from the ledge. The RMP’s large diameter wheels would be around 2 inches in diameter and the
other wheels would be half this size. The drivetrain for this design is similar to that of a zero turn
mower. The design would use a bucket to retain the cubes which will be complimented through
the use of a scissor lift. This lift would be used to move the bucket to the desired height when
dropping the blocks off into zone 3. In addition, a scoop would be attached through springs to the
scissor lift. As the scissor goes forward and back, it would contract and expand accordingly to the
motion of the scissor lift. The drivetrain for this design is similar to that of a zero turn mower. The
large wheels that are used while both collecting cubes and through the ping pong field are directly
driven by two independent motors and can be driven in opposite directions. This will produce a
yaw moment and turn the RMP in a very tight manner.
The second design concept (see Figure A.2 in the appendix) utilizes a belt-driven pickup
mechanism to load cubes onto the storage mechanism, which doubles as a bucket. The motor
design would allow the belt to move sideways at the bottom for a block to enter, then close and
lift to drop the block into the bucket. There would be a physical stop at the top that guides the cube
into the bucket. The bucket would be controlled by a mechanism that converts a motor’s rotational
motion into linear motion. The linear actuator would be placed close to the hinge which maximizes
the control that the linear movement has on the position of the bucket. This allows for accurate
tipping and dumping of blocks into zone 3 for RMP 3 to pick up. The wheels are sized so that they
create space under the RMP for ping pong balls to move freely. The majority of the weight of the
bucket will be placed towards the back end in order to ensure the RMP is balanced. The bucket
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will provide a large target for RMP 1 to transfer cubes to and will easily and quickly transfer cubes
to zone 3 when it reaches the barrier.
The third design concept (see Figure A.3 in the appendix) focuses on versatility and
prioritizes compact packaging. The major features of the design are an intake mechanism with a
set of small wheels, directly driven on a defined track. These wheels move an arm that extends out
from the vehicle around all the cubes in zone 2 and then pulls them onto the base of a ramp. The
ramp has several functions. In addition to being a key part of the intake mechanism, it also serves
as the primary means of passing cubes to the next zone. It accomplishes this through the use of a
motor mounted 12 inches above the left rearmost wheel. This motor winches the ramp up to a
height great enough to force the cubes to slide down the ramp and into the next zone. The ramp is
fixed on the right hand side at a height just greater than, or equal to, the height of the wall.
However, when the ramp is winched only halfway, due to a pivot point in the middle of the ramp,
it can serve as a “bucket” to receive blocks from other zones and transport them across zone 2. The
drivetrain for this design relies on the same principles as the drivetrain of a tank, a bulldozer, or a
zero turn mower. In this design, the battery and control box would be mounted as near to the center
as their height allows under the ramp in order to move the CG to as near to the center and as low
as possible.
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Table 2: Pugh Chart
Requirement Weight
Design Concept
1:
Three sets of
wheels with
bucket
Design Concept
2:
Belt pickup with
bucket
Design Concept
3:
Pulling intake
with winch and
ramp
Ability to pick up
5 zone 2 blocks on
the ledge
4 0 2 3
Ability to receive
6 blocks from
RMP 1
4 0 0 0
Ability to
continue
functioning after
driving off the
ledge
5 0 1 1
Ability to move
through ping
pong balls
5 0 0 0
Ability to transfer
all blocks to zone
3
4 0 3 3
Manufacturability 3 0 -2 -3
Maneuverability 4 0 -1 0
Adaptability 3 0 0 1
Total 0 15 23
The Pugh chart (Table 2) served as an excellent tool to compare the pros and cons of our
three potential designs. Design concept 1 was chosen as our baseline because it was the least
consistent in its ability to pick up cubes from our own zone. It is also the riskiest of the other
three designs, because the flipping motion would result in a high impact force that has the
potential to dislodge electronics and/ or break other components. All three designs implemented
big wheels, so they all scored the same in terms of ability to move through the ping pong balls.
Design concepts two and three both scored higher than design concept one in most categories.
However, design concept two scored lower in terms of maneuverability because it did not use the
same drivetrain system as design concepts two and three. In these two designs, the right hand
wheels are directly driven by two independent motors and can be driven in opposite directions
producing a yaw moment, turning the RMP with a very small turn radius. We also decided that
the pulling intake arm of design three is a more effective way to pull in cubes than the belt intake
of design two and the scoop of design one, so it scored higher in its ability to pick up zone 2
cubes from the ledge. The third design additionally scored higher in adaptability because the
ramp could serve dually as a dumping and receiving mechanism, and could easily change heights
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depending on the situation. Although the third design was harder to manufacture than the other
two designs, it scored high enough in other areas that it still was our best design concept overall.
Figure 4: Final Sketched Design Concept of our RMP
Our final design concept took all of these rankings into account, and combined aspects of all three
initial design ideas. We decided on our design by taking the best parts from each original idea, and
tweaking some of the ideas to improve them even further. The final design has big wheels
(implemented from all three designs), a more complex version of the pulling intake mechanism
from design concept three, a bucket that is a combination of the receiving/ dumping mechanism in
design concepts two and three, and the drive system used in design concepts one and three. All
four of the major subsystems are indicated in Figure 4.
The drivetrain subsystem uses one motor to drive a wheel on each side of the RMP so the RMP
will be able to turn in a very small radius. This drivetrain system will allow the RMP to be more
mobile on the ledge and make fine adjustments to make picking up blocks easier.
The RMP intake subsystem is similar to the one used to drive a steam locomotive. This is refined
from the system design concept 3 used to pull the blocks. The RMP will drive up to the cubes in
Zone 2 and one motor will rotate a lever that in turn pushes a plate up and out on another lever.
When the first lever turns past the halfway point the second lever will go down and back pulling
the blocks onto the bucket of the RMP. This subsystem is critical to fulfill our requirement of
picking up all five zone 2 cubes at once.
Bucket Subsystem
Intake Subsystem
Frame Subsystem
Drivetrain Subsystem
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The bucket subsystem is a storing mechanism that can double as a receiving mechanism (similar
to design concept 3), and can receive all six cubes from zone one at once due to its wide surface
area. The end of the bucket is fixed at the same height as the wall so the actuator that lowers the
bucket can also raise the bucket to dump cubes over the wall and into Zone 3.
The frame subsystem structure and dimensions are mostly dependent upon the other three
subsystem dimensions, and provides structure, rigidity, and mounting areas for all of the RMP
components.
To recap, the RMP interacts with the table, cubes, and other RMPs during the game in the
following ways: It drives along the ledge, and uses the linear to rotational actuator to extend the
intake arm and then rotate it back to pull the zone 2 blocks into the flat bottom of the bucket. It
will then use the precise turning control of the drivetrain to turn on the ledge and drive straight off
the ledge into the ping pong balls. The center of mass will need to be low enough that it does not
roll over while preforming this task. The bucket can be lifted up while the RMP drives so that the
ping pong balls will not interfere with the stored cubes. The ping pong balls will ideally slide under
the RMP frame with little interference as the RMP travels to wall between zones 2 and three to
dump out the cubes. The bucket actuator can rotate all the way up so that the bucket tilts and
becomes a slide for the blocks to travel down and into zone 3. The bucket will then be able to
lower again so that it can act as a type of “basket” to receive cubes from the zone RMP directly.
3.4. Analysis (10 points)
In this subsection certain calculations will be analyzed. Such calculations include, why and how
we choose which motors to use for our different subsystems, as well as the thought process behind
designing the wheels.
3.4.i Motor Selection for the Drivetrain:
We calculated the torque output of every motor, using the highest gear ratio for each (344:1 for
the double-gearbox and 400:1 for the planetary gearbox. The metal gearmotor has a built-in ratio
of 99:1). The metal gearmotor produces by far the most torque. Since a higher torque production
means a higher speed, we decided to use two metal gearmotors for our drivetrain.
*Note: Made the assumption that the efficiency of the metal gearmotors is 100%. This is an
assumption we made throughout our calculations. We made this assumption because the 99:1 gear
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is internal, so the efficiency would already be included in the measured output torque value of
1.13Nm found through experiments done in the lab.
3.4.ii Driving Torque Analysis:
We calculated the driving torque of one wheel based on the worst-case scenario of when our RMP
is descending from the ledge. This is the worst case scenario because almost all of the weight is
placed on the front two wheels, which is the maximum load the motor will every have to handle.
The normal force described by the variable N1 for one front wheel would be half of the total mass
of the vehicle. The total mass after all of our design changes was calculated by assigning the correct
materials to every part of our updated CAD model, and is 2.698kg. By summing the moments
about the center of the wheel we find that required driving torque is equal to the force of friction
multiplied by the radius of the wheel. We had to make another assumption for the coefficient of
friction. Since we covered the front wheels in rubber bands, the coefficient of friction between
rubber and the plastic material of the ledge of the arena is greatly increased. We therefore were
able to more efficiently use our motor torque output to move forward, and the calculations above
show that the motor does produce more than enough torque to drive, even in this worse-case
scenario.
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3.4.iii Runner Analysis:
We performed a runner analysis based on one of the functional requirements we set for ourselves
to be able to travel the distance from the edge of the ledge to the drop off point at the barrier of
zone 3 (1.3599m) in 15 seconds. We had to make the assumption that the Fl value, the internal
transmission force, is dependent upon the internal friction of the bearings. Through research we
determined that the internal coefficient of friction of roller bearings (uB) are approximately .005,
as found on the manufacturer’s website1
. We made the same assumptions described in previous
parts, such as the efficiency of the metal gearmotor is 100%, and the mass of the vehicle is 2.698kg
from CAD analysis. We found that we can easily travel much farther than 1.3599 m in 15 seconds..
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3.4.iv Bucket Torque Calculations
This is the analysis of the torque needed to lift the intake arm and pull in blocks. We assume that
the maximum force needed occurs at the point when the arm begins pulling in the 5 blocks in our
zone. We also assume a static snapshot of that moment. Lastly, we assume minimal rotational
friction between the free fitting pin and components. We used the dimensions and angle obtained
from our CAD model as well as coefficients of friction based on research and testing the blocks
in the lab. We obtain the value of 54.15 for the minimum gearing ratio needed but we use 400:1
to give us the greatest control over the intake speed when given input.
The maximum torque required to lift the bucket is when the bucket is at a 90 degree angle with the
upright or perpendicular to the ground. In the calculations we put the bucket at this angle with the
maximum number of cubes we would have at any one point in time, six, at the very end. This
represents the worst case scenario when the motor would be under the most load. In these
calculations we assumed that there was no loss of efficiency in the stall torque that the manufacture
provided for the gearbox. We could not do calculations for how much resistance to motion the
motor provided when off so we were not able to confirm that the motor would not be back driven
when driving off the ledge. The stall torque for the metal gearbox motor is 1.13 N*m with an
assumed efficiency of 100%. This motor has enough torque to move the bucket with a factor of
safety of 1.33. The planetary gearbox on the other hand has a stall torque of only .013 N*m when
operating at 10% efficiency. Where the slower speed of the 400:1 gearbox would be better for
more control it does not have enough torque to move the bucket at all.
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3.4.v Intake Mechanism Calculations
This is the analysis of the torque needed to lift the intake arm and pull in blocks. We assume that
the maximum force needed occurs at the point when the arm begins pulling in the 5 blocks in our
zone. We also assume a static snapshot of that moment. Lastly, we assume minimal rotational
friction between the free fitting pin and components. We used the dimensions and angle obtained
from our CAD model as well as coefficients of friction based on research and testing the blocks
in the lab. We obtain the value of 54.15 for the minimum gearing ratio needed but we use 400:1
to give us the greatest control over the intake speed when given input.
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3.4.vi Wheel Calculations
Figure 5: Ride Height and Clearance Calculation for larger diameter wheels
As shown in Figure 5, the larger diameter wheels give the RMP clearance of 0.37 inches
when going off the ledge. This calculation is a repeat of the calculation done for design review
with an added exclusion zone of 0.51" below the RMP. This allows a margin for error in the
machining of components that will sit directly above this area, and unlike the design review
calculation with 3.63 inch wheels, the larger wheel diameter will allow the drive train motors
adequate space to sit in without contacting the ledge.
Figure 6: Ride Height and Ping Pong Ball Clearance
As shown in Figure 6, the larger diameter wheels give the RMP 0.07 inches of clearance
over the ping pong balls when including a 0.51 inch exclusion zone for the drivetrain motors and
control box bracket to sit in.
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Figure 7: CG Location when on the ledge for Tipping Calculation
As shown in Figure 7, when the RMP goes over the ledge with the undriven wheels leading, the
CG stays within the wheelbase meaning any roll moment will be resolved by the wheels. This
means that the RMP won't tip going over the ledge. This calculation is a repeated one from
design review updated and modified to accommodate the design changes our team made. We
proved this calculation with actual testing in the days leading up to competition.
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3.5. Final Design and CAD Model (6 points)
CAD models reflect the result of our analysis.
3.5i. Design Description
Figure 8: Isometric Views of RMP with bucket in raised cube-passing position.
Figure 9: Side, Rear, and Top view of RMP with CG shown by the pink arrow.
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Figure 10: Left and Right Isometric views of RPM.
Figure 11: Final RMP CAD with Bucket system highlighted in blue.
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Figure 12: Final RMP CAD with Intake subsystem highlighted in blue.
Figure 13: Final RMP CAD with Frame subsystem highlighted in blue.
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Figure 14: Final RMP CAD with Driven and Undriven Wheels highlighted in blue on the
left & right respectively.
Our RMP consists of four main subsystem: the frame, the bucket, the intake and the drivetrain (see
Figures 11-14). The bucket mechanism consists of a metal gearbox motor, a rotational to linear
actuator, a polycarbonate bucket, brackets that attach the motor and bucket to the frame, 1/4" steel
pins that allow free rotation and e-clips that constrain the parts on the pins (see Figure 11). The
motor turns the rotational to linear actuator and lifts the bucket 90 degrees upward. This upward
rotation is necessary to pass blocks over the wall into zone 3 (see Figure 8). The bucket has an
inclined lip at the bottom to facilitate the intake of blocks. It also features cutouts on the sides to
decrease the weight.
The intake mechanism utilizes a planetary gearbox geared at 400:1, a support bracket, a rotational
arm, an intake arm with a slot cut in it, a 3/8" aluminum pin mounted to a 3D printed arm on the
frame, and brackets that hold the motor and support bracket to the frame (see Figure 12). The
rotation of the arm connected to the motor moves the intake arm in an elliptical manner, lowering
the front of the arm to intake the blocks and then lifting up to restart the intake process. The intake
arm slides over the pin in order to allow linear and rotational motion of the arm.
The frame consists of two vertical uprights and two horizontal beams supported by two brackets
across. One bracket connects the two horizontal beams and supports the control box. The other
bracket connects the two vertical uprights and supports the bucket motor brackets. The frame also
has holes drilled into it to attach the other brackets as well as bearings to support the wheels (see
Figure 13).
The drivetrain consists of two metal gearbox motors with brackets, 3D printed wheels with key
slots, 1/4" steel shafts with key slots, e-clips to constrain lateral movement, and rubber bands to
increase the traction. The undriven wheels are laser-cut out of Delrin to decrease friction on the
ground when the RMP is turning and are attached to the frame with 1/4" steel pins and e-clips (see
Figure14).
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3.5.ii: Design of Each Manufactured Part
1a. Wheel Undriven: Two of these were produced. These wheels were produced using delrin and
have the diameter of 4.32 inches. They were made of delrin because delrin is light and because we
needed custom wheels to travel over the sea of ping-pong balls. These items are a part of the
drivetrain subsystem.
1b. Wheel Driven: Two of these were produced. These wheels were produced using PLA and have
the diameter of 3.63 inches. They were made of plastic because of plastics light weight qualities
and because we needed custom wheels to travel over the sea of ping-pong balls. The only change
was the addition of a key-hole. These items are a part of the drivetrain subsystem.
2a. Frame Rail Bottom Left: One of this part was produced. The rail was made using the 1x1”
Aluminum 90 degree angle stock. The frame on the bottom left has the length of 8.625 inches. The
frame was milled in order to add holes so that additional parts could fasten onto it. From our final
design concept we removed a second upright bracket from that side. Thus there are holes that
should not be there. This item is a part of the frame subsystem.
2aa. Frame Rail Bottom Right: One of this part was produced. The rail was made using the 1x1”
Aluminum 90 degree angle stock. The frame on the bottom right has the length of 8.625 inches.
The frame was milled in order to add holes so that additional parts could fasten onto it. This item
is a part of the frame subsystem.
2b. Frame Rail Upright Left: One of this part was produced. The rail was made using the 1x1”
Aluminum 90 degree angle stock. The upright left has the length of 10 inches. The frame was
milled in order to add holes so that additional parts could fasten onto it. The dimensions for the
rails depended on the height of the wheels. This item is a part of the frame subsystem.
2bb. Frame Rail Upright Right: One of this part was produced. The rail was made using the 1x1”
Aluminum 90 degree angle stock. The upright right has the length of 10 inches. The frame was
milled in order to add holes so that additional parts could fasten onto it. The dimensions for the
rails depended on the height of the wheels. This item is a part of the frame subsystem.
3. Y-Bracket: One of these parts was produced. The part is made using 1/16th
inches thick
aluminum sheeting. A waterjet was used to manufacture this item. The length of the part is 4.75
inches and it has the height of 1.876 inches. This item is a part of the bucket subsystem.
4. Bucket: One of these parts was produced. This part is made using polycarbonate material. The
thickness of the polycarbonate material is 1/8th
inch. The method to model this part involved using
a heat gun borrowed from the Wilson center in addition to a hand brake in the machine shop.
Heating the material made it flexible to bending. The profile from the side is 10.8 inches in height
and 7.8 inches in depth. Our final design varies slightly with our predicted model. Because of
thermal expansion, our bucket did not conform perfectly to the angled design we had thought
possible. However, it remains in our constraints and functions. This item is a part of the bucket
subsystem.
24. 24
5. Bucket Arm Long: One of these parts was produced. The bucket arm long is a part made out of
¼” thick aluminum sheet. The process used to produce this part was water jetting. This item is a
part of the bucket subsystem.
6. Bucket Arm Short: One of these parts was produced. The bucket arm long is a part made out of
¼” thick aluminum sheet. The process used to produce this part was water jetting. In addition, a
mill was used to create the #4-40 tap on the side of this part. This item is a part of the bucket
subsystem.
7. Quarter Pin: One of these parts was produced. The quarter pin is a part made out of 3/8” inch
aluminum rod. The length of the piece is 0.68 inches with a diameter of ¼” it also has two grooves.
The part was manufactured using a lathe. This item is a part of the bucket subsystem.
9A. Bucket Motor Bracket: One of these parts were produced. This item used 1/8” square tube
stock. It was made on a mill. Location of the bracket changed slightly compared to the final design
we previously submitted as a consequence of providing support more efficiently for the bucket
motor. Furthermore, the bracket has a bushing press fit into it. This item is a part of the bucket
subsystem.
9B: Bucket Motor Bracket: One of these parts were produced. This item used 1/8” square tube
stock. It was made on a mill. Location of the bracket changed slightly compared to the final design
we previously submitted as a consequence of providing support more efficiently for the bucket
motor. This item is a part of the bucket subsystem.
11. Bucket Motorshaft: One of these parts was produced. This item used the 3/8”
aluminum rod.
The length of this piece is 1.56 inches with the diameter being ¼”. In addition to being
manufactured on the lathe, the use of a mill was necessary to manufacture the pin holes present.
This part has been changed from the original because we are no longer using set screws but pins.
This item is a part of the bucket subsystem.
12. Controlbox Bracket: One of these parts was produced. This item used the 1/16th
aluminum
plate. The process used to manufacture this part was the waterjet as well as a hand brake to make
the bends in the plate. The bracket additionally has Velcro on it in order to secure the batter and
control packs. This item is a part of the frame subsystem. This item has changed slightly since our
final design concept because of the bends not being completely 90 degrees in nature. This item is
a part of the drivetrain
14a. Intake Main: One of these parts was produced. This item used the 1/16th
aluminum plate. The
process used to manufacture this part was the waterjet as well as a hand brake to make the bends
in the plate. The arm varies from our final design concept due to us eliminating the second upright
on the left side of the RMP. The upright was causing buckling in our system and therefore we
removed one side of the intake main. This item is a part of the intake subsystem.
14b. Intake Arm Long: One of these parts was produced. This item used the ¼”aluminum plate.
The process used to manufacture this part was the waterjet. The final design plan called for the
production of two of these arms, however after testing and noticing that the intake subsystem
would buckle, we removed one of the intake arm longs. This item is a part of the intake subsystem.
25. 25
15. Intake Upright Bracket: One of these parts was produced. This item was made using PLA and
a 3D printer. The final design plan called for the production of two of these uprights, however after
testing and noticing that the intake subsystem would buckle, we removed the upright bracket
opposite the side with the intake motor. This item is a part of the intake subsystem.
16. Intake Pin: Two of these parts was produced. This item was made using the 3/8th
aluminum
rod. The final length of the parts was 0.7 inches and had the diameter of 3/8th
inch. There are two
grooves in each of these pins. These items are a part of the intake subsystem.
17. Intake Small Arm: One of these parts was produced. The items was made using the ¼”
aluminum sheet. The process used to manufacture this part was the waterjet. In addition, there was
a set screw hole put into the part thus a mill was additionally used. The item is a part of the intake
subsystem.
19. Intake Motor Mount: One of these parts was produced. This part was made of the 1/16th
aluminum sheet. The process used to manufacture this part was the waterjet. In addition, the
handbrake was used to make the bends necessary for attachment. This item is a part of the intake
subsystem.
20. DriveTrain Driven Shaft: Two of these parts were produced. These parts were made out of the
3/8th
aluminum stock. The length of the shafts is 1.75 inches. A variety of machines were used to
produce this part including the lathe and mill. The shafts changed from our final design plan based
off of the addition of a key slot. These items are a part of the drivetrain subsystem.
23. Pillow Block: Two of these parts were produced. These parts were made from 1x1” and 1/8”
inch thick aluminum stock. The process used to manufacture these parts included the mill. These
items are a part of the bucket subsystem.
25. Bucket Bracket A: One of these parts were produced. This part was made from ¼” thick
aluminum sheet. The process used to manufacture this part included the waterjet. This item was
modified slightly from our final design concept to incorporate better support for our bucket motor.
This item is a part of the frame subsystem.
26. Shaft Undriven: Two of these were produced. They are made with 3 grooves on them to mate
with the undriven wheels. They are made of aluminum and have the length of one inch and were
produced on the lathe.
34. Quarter Pin Short: Three of these were produced. They are made with aluminum and are a
length of 0.5 inch. They have two grooves and are located in the bucket system. It was used in the
bucket subsystem and produced on the lathe.
37. I bracket: One of these was produced. This was made with 1/16th
aluminum plate with the
waterjet in the autolab. Has the length of 4.75 inches. This is located in the bucket subsystem.
38. Intake Motor Mount: One of these was produced. Was made out of 1x1 aluminum stock. It is
used in the intake system to provide support for the motor shaft. This part was not in the original
final design plan, it was added to provide support. A mill was used to do the machining of the part.
26. 26
39. Key driven shaft: Two of these were produced. The keys are made of PLA with the use of a
3D printer. The dimensions of it are 0.125x20.125x0.5 inches. We choose to 3D print this part
because we were under a time constraint for milling time and the 3D printed part would fit better
without adding extra weathering to the shaft or wheel.
42. Intake Shaft: One of these was produced. The intake shaft acts as an extension to the planetary
gear box shaft. It has the diameter of a quarter inch and the length of 2.25 inches. A lathe was used
to make this part. It is located in the intake subsystem.
4. PROTOTYPE MANUFACTURING (6 points)
Once the prototyped idea was settled, manufacturing was necessary in order to understand the
issues that can come with scaling the RMP. Additionally, for the manufacturing several
manufacturing methods were used using a variety of materials.
4.1. Manufacturing Process (4 points)
Throughout the manufacturing of our RMP we used water jetting, milling, lathing, bending, laser
cutting, thermoforming, and 3D printing. We had to use the water jet twice because we were
cutting parts out of two different thicknesses of aluminum plate. For the water jet parts we had the
water jet cut the holes as opposed to drilling them after the parts were cut. The water jet was
accurate to within our tolerances leaving only set screw holes to be drilled on the mill to finish
those parts. All of our motor shafts and pins were made on the lathe. The concentric holes and
groves were cut on the lathe leaving the set screw/spring pin holes and key slots to be finished on
the mill after the shaft was cut to size. All of the drilling for our parts was done on the mill for
higher accuracy. We also used the mill to make motor brackets as well as the frame and pillow
blocks. We used the hand brake to bend both sheet metal brackets and the heated polycarbonate
for the bucket. Bending the bucket was a very difficult process. The polycarbonate had to be heated
along the bend line using a heat gun then bent using the hand brake. Both the wheels and the intake
mounts were 3D printed using the Cube printers. We used other miscellaneous shop tools,
including the band saw, to rough cut stock and the arbor press to press bearings, shafts, and
bushings.
During assembly we ran into some problems with tolerances and packaging that led to parts being
remade or modified. Due to the thin walls of the motor shafts, we couldn’t give the set screws the
thread engagement to hold. We had to drill the motor output shaft and pound in spring pins for all
of the motors. When we put the intake motor mount on the frame it interfered with the bucket
actuator. The solution to this was to make a new, longer motor shaft and move the actuator towards
the outside of the RMP and away from the motor mount. All of the pins and shafts were too tight
to get through the bearings leading to all of them getting sanded down or turned down on the lathe.
One of the bucket motor mounting brackets was bent when trying to press the bushing into it so
that bracket was completely remade on the mill. When we started testing in the ping pong balls we
found our RMP was not able to clear the balls like we had planned. The first solution was to use
wide rubber bands to build up the wheels as well as provide traction for the driven wheels, as seen
in Figure 16 on page 30. This worked well but for the un-driven wheels the rubber provided too
much grip to allow us to have a small turning radius. We had not used any of our delrin so we took
27. 27
the sheet from the kit and cut new front wheels using the laser cutter. These new wheels provided
the clearance as well as slipping ability for our RMP. The intake was modified to rotate with only
one mount to keep from binding up on the un-driven side. This change was made by taking the
intake to the shear and cutting one side off.
4.2. Bill of Materials (2 points)
Majority of our parts were made out of Aluminum, as seen in our Bill of Materials, Table 3.
Aluminum was the most cost-effective material to use since we were provided so much of it in
out kit. However, there were a few other parts that were made using different material. Our
driven wheels were made out of 3D printed PLA because it is a light material, and we needed
wheels that were the correct diameter for our frame to fit over the ping pong balls. The undriven
wheels were made out of delrin because it allowed for smoother turning than the PLA. Our
Bucket was made out of polycarbonate because it is a lighter material than most, and also
because it can be heated up and bent to whatever angle we want. It is very hard to bend
aluminum or other metals in the shop to anything other than 90 degrees. A few of our shafts were
made out of steel because they are more rigid, and also because the steel rod was the exact
diameter we needed. Finally, the intake upright bracket was made out of PLA because due to the
unique design of the part, it would be very difficult to make any other way.
Table 3: Bill of Materials
Part # Description
Material
Dimensions Supplier
Total
Quantity Price
1a
Wheel
Undriven
Delrin 12” X 12”
X 1/8” Crib 2 --
1b
Wheel
Driven
3D printed
material (PLA) Crib 2 --
2a
Frame Rail
Bottom Left
Aluminum
90 degree angle
stock
1" X 1",
1/8" Alro (kit) 1 --
2aa
Frame Rail
Bottom
Right
Aluminum
90 degree angle
stock
1" X 1",
1/8" Alro (kit) 1
(trade
in with
1/4")
2b
FrameRail
Upright
Right
Aluminum
90 degree angle
stock
1" X 1",
1/8" Alro (kit) 1 --
2bb
FrameRail
Upright left
Aluminum
90 degree angle
stock
1" X 1",
1/8" Alro (kit) 1 $3.40
3 Y Bracket
Aluminum plate,
1/16" thick 12 x 18 Alro(kit) 1 --
28. 28
4 Bucket
Polycarbonate
12 X 15
Michigan
Hybrid
Racing 1 $15.63
5
Bucket Arm
Long
Aluminum plate,
1/4" thick 12 x 18 Alro (kit) 1 --
6
Bucket Arm
Short
Aluminum plate,
1/4" thick 12 x 18 Alro (kit) 1 --
7 Quarter Pin
12L14 Carbon
Steel Tight-
Tolerance Rod
1/4"
Diameter,
1' Length
McMaster
(kit) 1 --
8
Metal
Gearmotor given crib 3
(trade
in)
9A
Bucket
motor
Bracket 9A
2x1 (1/8)" square
tube stock
12 x 18 Alro(kit) 1 --
9B
Bucket
Motor
Bracket 9B
2x1 (1/8)" square
tube stock
12 x 18 Alro(kit) 1 --
10 Bushing
Flanged brass
bushing
given: 1/4"
ID, 3/8"
OD
McMaster
(kit) 3 --
11
Bucket
Motorshaft
Aluminum rod,
3/8" diameter 18 Alro(kit) 1 --
12
ControlBox
Bracket
1/16" Aluminum
Plate 12 x 18 Alro(kit) 1 --
14a Intake Main
Aluminum plate,
1/16" thick 12 x 18 Alro(kit) 1 --
14b
Intake Arm
Long
Aluminum plate,
1/4" thick 12 x 18 Alro(kit) 1 --
15
Intake
Upright
Bracket
3D printed
material (PLA)
Crib 1 --
16 Intake Pin
Aluminum rod,
3/8" diameter 18 Alro(kit) 2 --
17
Intake Small
Arm
Aluminum plate,
1/4" thick 12x18 Alro (kit) 1 --
18 Intake Motor
Planetary
Gearbox
Pololu
(kit) 1 --
19
Intake Motor
Mount
Aluminum plate,
1/16" thick 12 x 18 Alro(kit) 1 --
29. 29
20
DriveTrain
Driven Shaft
12L14 Carbon
Steel Tight-
Tolerance Rod
1/4"
Diameter,
1' Length
McMaster
(kit) 2 --
23 Pillow block
square Aluminum
tube stock
1x1 (1/8)"
18" long Alro(Crib) 2 --
24
Bearing
Flanged
Filanged ss
Bearing given
McMaster
(kit) 6 --
25
Bucket
Bracket A
Aluminum plate,
1/4" thick 12 x 18 Alro (kit) 1 --
26
Shaft
Undriven
12L14 Carbon
Steel Tight-
Tolerance Rod
1/4"
Diameter,
1' Length
McMaster
(kit) 2 --
27
Polulu
Bracket
given
given Crib 2 --
28a Half Bolt 1/2" given Crib 25 --
28b Bolt
3/4"
given
McMaster
(crib) 12 --
34
Quarter-Pin
Short
12L14 Carbon
Steel Tight-
Tolerance Rod
1/4"
Diameter,
1' Length
McMaster
(kit) 3 --
35 E-clip-.25
given
1/4" Dia.
McMaster
(crib) 6 --
36 E-clip-38
given
3/8" Dia.
McMaster
(crib) 4 --
37 I-bracket
1/16" Aluminum
Plate 12 x 18 Alro(kit) 1 --
38
Intake Motor
Mount
aluminum tube
stock, 1/8" 1 X 1 X 12 Alro(kit) 1 --
39
Key Driven
Shaft
3D printed (PLA) .125 X .125
X .5 Alro (kit) 2 --
40 Nut
given 1/4"
diameter
McMaster
(crib) 33 --
41 Washers 4 --
42 Intake shaft
12L14 Carbon
Steel Tight-
Tolerance Rod
1/4"
Diameter,
1' Length
McMaster
(kit) 1 --
43 4mm nut given 4
44
1/16th
spring
pin
Given
1/16th
diameter
McMaster
(Crib) 3 $0.50
45 Mob Grip
Bought
4in X 4in
SkateShop
Ann
Arbor 1 $2
30. 30
5. PROTOTYPE TESTING (8 points)
Testing was necessary before the final competition to ensure the functioning of our RMP.
Additionally, squad testing was necessary in order to modify any changes in each individual
zone’s strategy. Prototype testing helped finalize the final zone strategy.
5.1. Preliminary Test (3 points)
These were individual tests and issues we faced before we would be able to test as a squad.
5.1.i Issues that prevented testing
Before the squad scrimmage/test, we had a completely manufactured RMP and two out of three
working motors. None of the teams had a completely functioning robot, so an official scrimmage
did not happen on the day it was planned, it happened the Wednesday before competition.
Our planetary gearbox was not responding to power so we took it off the mount and tested it with
a different power source. It became very obvious that the soldering was not the issue, and that
something was going wrong internally. We took it apart, re-assembled and lubricated the gears,
and then it worked well again. Our bucket and drivetrain motors were working very well. However,
the set screws would not stay in, and many would not even latch onto the shafts at all. We
concluded that the shaft walls were so thin that the set screws either did not have enough threading
to latch on to, or that they needed additional support to stay in. This was an issue that prohibited
us from proceeding to any further testing.
In order to fix this issue, we made flat surfaces at the end of two of our shafts so that the set screws
had a greater area to set on to. This method unfortunately did not work on the set screws attaching
the three motors to their respective shafts, which was a dilemma because those are the connections
that we needed to be most secure. To ensure that the shafts would not begin to spin relative to the
motor, we drilled holes in all three motor shafts themselves and added 1/16th
spring pins. This
worked well and allowed us to begin testing of all three of our moving parts.
5.1.ii Testing, Issues found during testing, and Design changes made
After we fixed the set screw issues, we were able to begin official testing. The first thing that we
tested was the bucket because it is our MCS, and we wanted to make sure that the motor could
handle all of the torque that it provided. It looked like it lifted pretty effortlessly the first time we
tried it, but once we added cubes the bucket could not lift past the point where it was horizontal.
By altering the trim on the controller, we were able to get the bucket to raise the full distance.
However, when the rotational to linear conversion linkage passed fully vertical the load rotated
linkage back down quickly, and we were unable to hold the position needed for the blocks to
smoothly slide out of the bucket and into the next RMP. We assumed that the motor must have
been approaching its stall torque already, and the weight of the cubes pushed it over the edge. In
order to fix this issue, we took weight off of either side of the bucket by cutting down the side
walls (see Figure 15). We took off a total of 2.3 ounces, and tested to make sure that the blocks
could still be contained well by the lower walls. We re-tested the bucket, and found that it could
rotate up in 1.25 seconds, which far exceeded our expectations from original calculation that the
bucket could complete a full rotation in 3 seconds.
31. 31
Figure 15: This figure shows the before and after CAD models of the bucket. The image on
the left shows our bucket before we tested it with the motor. The image on the right show
the bucket after we took off about 2.3 ounces of weight on either side.
Next, we tested the intake mechanism with the motor. We realized that the current orientation of
the intake with two arms rotating created too much bend and stress on the front piece as the non
driven side would buckle. Only one arm of the intake was attached to the motor, the other arm
lagged majorly and was unable to keep up. We were concerned that the front piece attached to the
two arms would break, and so we decided to eliminate one of the arms entirely, and chop off part
of the front pieces as well (See Figure 16). This ended up working out very well, and allowed the
intake to move quicker due to the reduction of weight and resistance provided by the other arm.
Figure 16: This figure shows CAD models of the intake mechanism before and after design
changes. The image on the left shows the intake before when it had both supports and arms
on either side. The image on the right shows the final intake mechanism with some of the
front part chopped off and one of the arms and supports removed entirely.
32. 32
We tested this modified intake mechanism and found that it could pull in blocks very well when
they were aligned in one row, but did not quite have the reach to pull in two rows of blocks at
once. We realized that we designed the intake to be able to extend 3 inches, but we did not account
fully for the thickness of the sheet metal itself that the intake was made out of, or the amount that
the bucket extended on the ground. One of our functional requirements was the ability to intake
all five cubes from our own zone at once, so we made a few changes. First of all, we added Mob
Grip, a sticky paper commonly used on skateboard decks, to the bottom of the intake mechanism
so that it could pull in blocks more easily. Then, we adjusted the span of the intake by moving it
out relative to the bolts and holes where it attached to the other two side arms. When we re-tested,
we found that it was able to extend the full 3 inches necessary to intake all 5 blocks at once.
Another issue that we did not foresee is that the bucket lifted slightly off of the ground a certain
distance depending on the length of the banana clips plugged into the control box. This was
something that we had not accounted for in CAD, because we did not realize the how long the
banana clips actually were. We had left enough space behind the bucket, but not enough. The
bucket had to be able to fit flush with the ground, so we figured out the exact angle the bucket had
to be at relative to the control box clips and re-bent the bottom flap. Then, we were finally able to
intake all of the blocks consistently into the bucket and fulfill the functional requirement of in
taking all 5 blocks from our own zone.
Finally, we had to test the drivetrain. It worked flawlessly on flat ground, and we were able to
successfully descend from the ledge into the sea of ping pong balls, which fulfilled one of our
functional requirements. And yet, once we got into the sea of ping pong balls, we got stuck because
all of the ping pong balls pushed up against the frame and began to build up against the wall. One
of our functional requirements was to be able to travel across the ping pong balls, so we had to
make an immediate change. We had originally designed our RMP to have a frame that was raised
high enough that it could pass over the ping-pong balls. However, in our frame calculations we
didn’t account for the additional depth of the frame rail below the center of the wheel. We also
didn't account for the fact that the motors sat lower than the base of the frame rail or that when
manufacturing the bracket that supported the control box, we were unable to control the bends as
accurately as we thought we could. This meant that the control box bracket developed a slight bend
across its base. This bend also sat below the bottom of the frame rail and also contracted the ping
pong balls.
We fixed this issue by adding multiple layers of thick rubber bands to the driven wheels to improve
traction and increase the height that the frame lifted off of the ground. We discovered through
experimentation that a total of 15 rubber bands provided the necessary height to clear the ping
pong balls. The new diameter of the wheels became 4.32 in. Upon further testing, we found the
rubber bands on the front wheels made it more difficult for the RMP to turn because the front
wheels dragged along the ground instead of smoothly rotating in opposite directions. We resolved
this problem by laser cutting new front wheels out of delrin that were the correct diameter without
the addition of rubber bands. (See figure 17). We tested these new wheels in the sea of ping pong
balls, and they worked even better than we had hoped. One of our functional requirements was to
be able to travel the distance from where we intake our blocks to the drop off point at zone 3
33. 33
(1.359m) in 15 seconds. This functional requirement was based off of our original runner analysis
calculations (see Section 3.4). We found that the RMP was able to descend from the ledge, travel
the distance of 1.359m, and turn a complete 180 degrees to get in perfect position against the wall
for passing in exactly 8.75 seconds. This result far exceeded the functional requirement of 15
seconds that we had set for ourselves. The new wheels and rubber bands not only improved our
ability to pass through the ping pong balls, but also improved the RMP's ability to turn.
Figure 17: The image to the left shows our 3D printed wheels before we were able to test.
The image to the right shows our 3D printed wheels after we re-machined the undriven
wheels, and put rubber bands over the driven wheels.
5.2. Scrimmage Results and Redesign Based on Scrimmage (3 points)
Although we did not have the official scrimmage on the day designated to it, our squad had a full
run-through on the Wednesday before competition. There were no other design changes necessary
at this point since we had changed so much already (see all design changes described in Section
5.1). The only slight malfunction was that a few rubber bands fell off the driven wheels when we
were turning, so we simply made sure they were more securely places. Our RMP was able to
receive blocks perfectly from zone 1 and pass blocks perfectly to zone 3. All four of our squad
robots were able to fulfil their functional requirements completely. We practiced and successfully
completed multiple block transfers between zone 1 and zone 3, and even as a squad were able to
get blocks all the way from zone one to the goal in zone 4. During this run-through with our squad,
we fulfilled our final functional requirements of being able to pass all five of our cubes to zone 3,
and accept all 6 cubes from zone 1 (even though the zone 1 RMP can only pass 3 cubes at a time).
Table 4 summarizes how our RMP fulfills all of our functional requirements and target values
discussed in both section 5.1 and this section.
34. 34
Table 4: A summary of our functional requirements and target values, and whether or not
they were fulfilled before or after major design changes.
Functional
Requirement
Fulfilled Initially
(yes/no)
Fulfilled after
Design Changes
(yes/no)
Pick up zone 2
blocks
Yes Yes
Pick up all 5 zone 2
blocks
No Yes
Function after
traveling over the
ledge
Yes Yes
Travel through the
ping pong balls
No Yes
Travel 1.359 m in 15
seconds
No Yes
Receive all 6 cubes
from Zone 6
No Yes
Transfer All cubes
to Zone 3
No Yes
5.3. Discussion of Competition Results (2 points)
In the competition, squad 4 took first place and the second place team was squad 7. Our squad was
tied for last place with zero points scored. The day before the competition our squad testing went
very well and all zones successfully passed cubes to the next zone and scored points (as described
in Section 5.2). Our RMP was having bucket motor troubles so we started making arrangements
to have another motor ready for competition day just in case one was needed. Our RMP suffered
from two system failures on the competition day. The morning of the competition our metal gear
motor that controlled the bucket was working perfectly well so we decided not to swap the motors
out. When we got to the on deck table and got our RMP wired up the motor was not working. The
reason it did not work was because after constantly testing our RMP going off the edge, the bucket
which had to be held at a 90 degree angle going of the edge would “bounce.” By bouncing, the
motor would slowly be back driven. We believe that this is the reason that our motor stopped
functioning. We got the motor to work intermittently and had to go into the competition like that.
The second problem was control related where the drivetrain controls were backwards and the left
handed controls were linked and unlinked throughout the match. Further investigation revealed a
faulty control box was the cause for some of the wiring issues, however the validity of that claim
cannot be confirmed. The zone one and zone three RMPs both suffered from mechanical failures
that kept them from passing cubes whereas zone four got the cubes but missed the goal and ran
out of time. Zone one initially struggled to get over the pyramid but when they did they picked up
all of the cubes. The problems developed when the RMP got back to the wall with zone two and
were not able to pass the cubes because the system that raised their bucket would not go up all the
way. Zone three broke a set screw off in the RMP and was rendered unable to pass cubes. The
35. 35
performance of our RMP could have been improved if the controls had worked without issue. The
bucket motor working only some of the time was a problem but we could have gotten points
anyway. Our squad had a good strategy and it came off very well in the practice but on the day the
mechanical and electrical failures kept our squad from following through with it and resulted in
zero points.
6. DISCUSSION AND RECOMMENDATIONS (5 points)
Here we reflect on the prototype and what changes we would make to our RMP as well as the
competition.
6.1. Project Summary (2 points)
In summary, our RMP’s role was to transport our own cubes into zone 3 as a priority and then
collecting zone 1’s cubes to then transport to zone 3. In order to complete both of these tasks while
adjusting to our difficult environment, we had to incorporate intake as well as drop off designs.
Our principal functional requirement was collecting all five of our cubes from our zone in one
attempt since we could not retrieve cubes after we decline from the ledge. Furthermore, we
required ourselves to have the capacity of receiving all 6 cubes from zone 1’s RMP to reduce the
amount of trips we would otherwise need to make. As a consequence of acting as a transport
service for the cubes being received from zone 1, we must be able to navigate through ping-pong
balls, or in our case travel over. A consequence of traveling over however raises our center of
gravity which brings the fourth functional requirement, the ability to come down from the two inch
ledge. To meet and go beyond these functional requirements we set out with a design that would
accommodate all requirements evenly as they are all intertwined in our team and squad strategy.
For our RMP we broke-down the design and production into four subsystems: frame, drivetrain,
intake, and finally bucket.
Our frame was built based on the requirement that we choose to travel over the ping-pong balls
instead of going through them. The result of this is that we are restricted with how low we mount
certain items. Motors, brackets, and screws were attempted to be made so that we would travel
with these least amount of hindrance possible. Our actual result reflected that our RMP didnot in
fact make contact with ping pong balls. However, the issues that arose were wear and tear on the
bucket motor as well as control box issues. Our RMP was set unfortunately compete a day too late
as the testing took a negative toll on our RMP. We were unable to score any points in competition.
Our drivetrain consists of two Polulu 99:1 metal gear motors. Based off of data used in labs as
well as analysis presented in the analysis section 3.5 on page 13. We were only confident in using
the 99:1 gear motor for this task. The weight of our RMP changed from the original design on
Solidworks software to the final produced model yet the motors provided enough torque for the
RMP to complete its tasks in trials.
Our intake varied greatly from original design to final production but maintained its same
functional idea. The intake extends 3 inches and then pushes the cubes into our bucket. The intake
uses the planetary gear box set up in the highest gear ratio of 400:1configuration. During
competition this subsystem performed well collecting 3 cubes.
36. 36
Our final subsystem, which was our most critical subsystem was our bucket. The bucket had the
requirement of acting as a basket as well as a slide. While the bucket’s production proved difficult
the most complicated part about the subsystem was the actuating system that would raise the
bucket. The actuating system required that several parts connected via e-clips, pins, and set screws
work. To raise the weight of the bucket and the cubes within.
To manufacture this RMP we utilized several machines such as the mill, lathe, water jet, and drill
press. In addition to these conventional machines we used other machines as well such as, grit
sanders, a dremel, a hot gun, an arbor press, and 3D printers. Generally we used two materials to
machine our parts, aluminum and PLA. When deciding whether we would machine or print a part
we considered the difficulty of machining the part while maintaining its design. We determined
that only the intake upright and wheels would require the 3D printing. Furthermore, the heat gun
was used in order to melt the polycarbonate. Under heat the material becomes easy to bend and
manipulate thus allowing us to shape it to our liking.
After the manufacturing of our RMP was complete, we proceeded to perform test in order to verify
that our specific requirements we met. For speed, we set a distance of 1.359m to be traveled in 15
seconds. We met this requirement in 8.75 seconds. We also calculated that the bucket could a full
180 degrees in 3 seconds. We found that the bucket could complete a 180 degree rotation in 1.25
seconds. The results showed that our theoretical analysis was very consistent with our
experimental results and in some cases even exceeded our requirements. Therefore, there were not
many adjustments made after testing besides tightening screws.
Overall, our squad did not perform well on the test day. That being said, everyone’s frustration at
the end of it was a direct indication that we all cared and were invested in the success of the squad.
Moreover, we were all committed to the project because of the time and effort we as well as our
main GSI Yihao put into it. The competition was certainly a failure for us individually, but we
were sad to see our GSI potentially not win once again.
Going forward though, I think we would set a better timetable. Yes deadlines should be flexible
but the deadlines we had allowed for members to act patiently without a sense of urgency at times.
I think going forward we also would need to think about the manufacturing plan while creating the
CAD model. We ran into too many difficulties because that wasn’t thought of during the designing
process. I think that our bucket and intake were very well designed and made. Perhaps we could
have machined both better, but we were only able to come to that conclusion when we started
testing our RMP. Overall, we are all proud of the product we put forward, we are disappointed in
the lack of success, but we are proud of our accomplishments as a group and a squad.
6.2. Recommendation for Mass Production (2 points)
There are a number of changes that would need to be made before our RMP could be mass
produced. To start with the assembly process of our RMP is too time consuming to be mass
produced. We would have to change to location of fasteners and the shape of some of the brackets
to speed up the assembly process. The materials used for the RMP would have to have some minor
changes. The stock used to make the frame would have to change to reduce the number of cuts
needed and speed up the machining time for those pieces. The stock used to make the bucket motor
37. 37
brackets would have to change because too many cuts are made and too much is wasted in the
manufacturing. One of the biggest changes that would need to happen is find a different
manufacturing process to make the bucket. Bending polycarbonate is too time consuming and
hands on to mass produce. The easiest method to use would be an additive manufacturing process
like 3D printing to make the bucket. It would also be a good idea to change the motors and
gearboxes to decrease speed and increase torque. This would allow for better control from the
operator and more reliable performance.
6.3. Future Project Idea (1 points)
The current project required much more creativity from the individual groups than the past years.
Last year the groups could make simpler robots while one group really worked hard to make
something work. There was a lot of inter squad collaboration. Here, everyone was able to work on
their own without really having to communicate with other squad people. I think a future idea
could be that there should be more collaboration with the squad. Realistically, we did not have to
talk a lot with other squads until the week before, while this may seem like a negative, it was not
as during the scrimmage we performed well as a unit. I think that this idea is best when it comes
to getting each group to really work hard. However, the time commitment may have been more.
Maybe a competition that involved the RMP’s to play soccer would be a cool task. Require the
RMP’s to “pass” two times before shooting. I think that this leaves a lot of teamwork on the table.
Squads would need to assign attackers and defenders and realistically RMP’s would be able to just
kind of clobber each other. Obviously rules would need to be amended in terms of scoring but that
would be really fun competition to watch.
7. REFERENCES
1. "Coefficient of Friction, Rolling Resistance, Air Resistance, Aerodynamics." <i>Coefficient of
Friction, Rolling Resistance, Air Resistance, Aerodynamics</i>. N.p., n.d. Web. 14 Dec.
2015.
2. ME 250 lecture slides provided on Ctools
3. Professors, GSI’s and our peer mentor
8. ACKNOWLEDGEMENTS
To those who made it possible. The nights that caused us stress were not for nothing, without your
help we would not have been able to grow in these 13 odd weeks. A special thanks to all of the ME
250 GSI’s who worked tirelessly to help us, especially Yihao Zheng. Help us beyond just approving
plans, but giving us their honest opinion when other people so often would rather sugar-coat issue.
Thank you to our lecturers, while the 9am lecture was always a difficult task to attend, both
lecturers always brought their enthusiasm and their love for engineering to the classroom. Thank
you for the knowledge and hosting such a wonderful class.
To those in the machine shop, the men who worked there who would never hesitate to answer your
questions. They knew how to teach when the teaching required hands-on activities. They too were
always keen on giving us their honest opinion.
38. 38
A special thanks also goes out to Shell our corporate sponsor. Without the funding the class would
have lacked more supplies than we would care to imagine.
40. 40
Figure A.3. Preliminary Design Concept Sketch 3
B. Dimensioned Drawings and manufacturing plans (4 points)
See attached documentation
C. PURCHASED AND TRADED ITEMS
It was necessary to purchase some additional parts in order to ensure the manufacturing of our
RMP. We additionally traded parts with other groups in our squad to ensure an efficient usage of
materials.
C.1 Purchased parts
Include the vendor, part name/number, price, a brief description of the need/use, and calculate
the total price of all purchased parts.
Supplier Part Name/ # Dimensions Qty Price ($) Description
Michigan
Hybrid Racing
Polycarbonate
Sheet
16” x 24” x
1/8”
1 15.73 Bucket
Material
Lowes JB Weld: 2
part epoxy
8 fluid oz 1 5.98 Seal cracks
formed in
machining
bucket
Lowes High Gloss
Black Spray
Paint
12 fluid oz 1 3.98 Obtain surface
finish for
cubes to slide
easily on
Skate Shop of
Ann Arbor
Skate Board
Grip Tape
4in X 4in 1 $2.00 Increase wheel
traction
41. 41
ME250 Shop Spring Pins 1/16th 3 $0.50 Hold Motor
output shaft to
adapting shaft
C.2. Traded parts (inter-squad)
Trade In Part Trade Out Part From Trade Deficits Description
Acrylic Plate,
double gearbox &
motor
MGM motor x2 Crib 9.29 + 8.35 –
19.76*2
Motor to power
bucket
ball caster wheel Bearing x2 Crib 4 – 5.62*2 Allow shaft
mounting for
bucket pivot point
¾” x ¾” x 18”
tube stock
Bushing x2 Crib 3.29 – 0.46*2 Support intake
shaft
JB Weld N/A Sold our Epoxy to
other ME250 team
+ $4 They asked teams
in the shop for
epoxy; we offered
ours. It wasn’t
returned.
1x1x18” ¼” angle
stock,
1” x 1” x 18” 1/8”
angle stock
Crib 5.29 – 3.4 Frame Material
Net deficit of -$49.05
