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MAE 3 Individual Robot Analysis

Archimedes Screw

Robot: Mickey’s Playhouse

Christian Heid (A12851225)

Section A03 Team 33: Mickey’s Playhouse

Part 1: Description of Component: (Overview of the Robot)

The robot, also known as Mickey’s Playhouse, gathers the balls (Pokeballs) at the middle of the table and scores them into

the elevated circular opening (Pokestop) at the left-rear of the table. The concept was inspired and centered around

Archimedes Screw and a U-Joint commonly found in steering assemblies. The design philosophy of the robot was to

create an optimally packaged 10x10x17.5-inch robot capable of retrieving and scoring all balls. At the starting orientation,

the Tube and Intake would be vertical. In scoring orientation, the intake is free to rotate at a hinge and the Scoring Screw

would rotate downwards to a static optimized angle. The design of the scoring component revolved around a way to create

linear motion perpendicular to the rotation plane using a single motor. The intake and screw combined can hold all 20

balls (10 in the Screw Assembly and 10 in the Intake). It also has a constant scoring potential as the screw continues to

rotate and load incoming balls.

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Overview of the Archimedes Screw

The Archimedes screw is made up of 2 parts: The Intermediary Screw (horizontal) and Scoring Screw (angled).

The horizontal Screw is 5.3 inches and transports the balls to the angled scoring Screw which is 15 inches long.

Both Screws are 2.5 inches in width and have an axle diameter of 0.5 inches. The Screw rotates in the counter-

clockwise direction to transfer balls, across in the positive x-axis in relation to the side view of the robot, to the

Scoring Screw, inclined at a 35-degree angle to a specified height of 11 inches in order to reach the highest goal

(5-point goal).

Minimum Set of Functional Requirements (FRs)

Enough torque to overcome binding at the joint and friction of the system and rotate screw

Take at most 10 seconds from intake to score

Collapsible in height

Flexible at joint

Overview of How the Component Functioned

The Archimedes screw performed beyond expectation. The transition from the Intermediary Screw to the Scoring

Screw took some adjusting of the Top Tube Chute Bracket, but once dialed in made the transition flawlessly. The

GM-2 torque motor was enough to overcome the friction between the 3D printed Screw and 3D Printed Tube

Chute. The addition to the Bracket allowing for collapsibility of the screw

in transition from starting orientation to scoring orientation, it also

reduced much of the existing friction because it elevated the screw

above the contact surface. The Screw stows upwards with clearances cut out

in the Tube Chute for retaining walls to pass through, The Scoring

Screw itself rests with high precision on the Intermediary Screw

when upright (Fig. 3). When deployed, the distance between

the two screws maintains its 0.1-inch clearance (Fig. 4).

The only areas of improvement were concluded to be the cycle

time. It averaged 11.2 seconds for time taken from intake to score,

a 12% deviation from our ideal.

Fig. 3 Fig. 4

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Part 2: Project Management Reflection – Risk Reduction Tests

This reflection will look at the Risk Reduction Test and the things learned from it, which were then

implemented in the final design. The greatest design challenge was the issue of the Scoring Screw being

pulled down by gravity and torsion at the joint, through the string, into the Intermediary Screw. It caused

damage to couplings and broke a couple Screws when the couplings would wrap in on themselves, thus

applying torsional loads they were not mean to withstand and failing as a result. Redesigning the Screw or

Chute was not an option.

The reason this design challenge became such an issue for us was that our risk reduction was done at at

optimal angle for the Screw to function, not to score. Too much creative liberty was taken in making

concept generations work, and did not carry out a Risk Reduction that adequetley addressed aspects of the

design function during compeition. It worked in designing the Screw, but not in the practice of the Screw.

The incline and pitch of the Scoring Screw are much less in Risk Reduction than on the final design. From

the pictures shown, they have the same amount of thread but different spacing. The Risk Reduction Screw

was 8 inches long and weighed 143 grams.

The final design was almost twice the length,

15 inches, weighing 227 grams. The final

design was 87% longer and 60% heavier. The

increased incline combined with the increased

weight added more axial force down into the

joint of the two screws. The problem was that

trying to prop the Screw up using its axle can

work when stationary, but when rotating the

contours of the screw rotate upwards,

interfering with the support.

The solution was the creation of the Tube

Chute Bracket circled in red at the bottom left

of the page. A 10-32 “bolt" was threaded into

the Scoring Screw with a clearance hole in the

Bracket. The progression of the Screw can be

seen in the sequence of images shown below.

The free travel of the bolt seen at the top of

each picture, through the Bracket, lets the

screw fall into position, but stop at a pre-determined distance from the Intermediary

Screw. It supports the weight of the Scoring Screw at the Bracket instead of at the

joint, and eliminates the couplings from wrapping in on themselves.

Original Risk Reduction

Final Design

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Part 3: Analysis of Component

Objective of Analysis:

The objective of this analysis is to predict the maximum torque needed by the motor to rotate the Screw

Assembly, taking into account factors of the entire system. Calculating the torque required to rotate the

screw can help make design decisions on whether changing 3D printing materials or the orientation during

printing so that the finish on the inside of the screw in smooth. Currently supports were used to print both

the Screws and the Tube Chute. It can also help guide our competition strategy. The concept of the screw

was to store balls while simultaneously scoring them, and having more balls in the system will cause greater

downward force and friction at suspension points.

Free Body Diagram

Front of Intermediary Screw

Side of Screw Assembly

FBD BALL ROTATION

Front of Intermediary Screw

FBD BALL ON SCREW

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Energy Power Analysis

Assumptions: o There is no energy loss inside the system, so the heat generated by friction is

negligible.

o The motor accelerates quickly and time required to reach max velocity is

negligible

o Since the Screw is suspended, it acts similar to that when it is completely

horizontal.

Energy Source:

o A GM-2 is the source of rotational force. It is mounted directly into the

Intermediary Screw through an indentation in the Screw. The energy is transferred

through the system by the coupling located at the joint.

GM-2 Max Power: 0.356 W

GM-2 Max Energy in 40 seconds: 0.356 W * 40s = 14.24J

Energy and power required to achieve motion of component: o The total energy needed to rotate the screw uses the moment of inertia for a solid

cylinder with a mass and radius.

Energy Needed:

Energy Available:

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Factor of Safety (Energy):

Power Needed:

Factor of Safety (Power):

Force / Torque Analysis

Assumptions:

o The Screw is full with balls

o The Screw is suspended at two points

o Since the Screw is suspended, it acts similar to that when it is completely horizontal.

o There is a force of friction cause by the ball rotating inside the screw that provides

a resisting force against the motor.

Relevant Equations:

o Friction of Balls: F btotal ≔F ball1 ⋅ n balls F ball1 ≔M ball ⋅ g

o Friction of Screw F screw ≔M screw ⋅ g

o Angular Acceleration: a ≔(noload/ tchange)

o Torque of Friction: T friction ≔Ffric ⋅ R

Torque Needed:

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Torque Required:

Factor of Safety (Torque):

Measurement of Component Performance:

I first relieved the Screw Assembly from the Chute Tube encasement. The Screws could lay flat,

but still elevated above the bottom surface so that there is to friction across the screws. The Tube

Chute Bracket was removed from the Tube Chute as well and served as the stand which elevated

the screw. The entire Screw assembly, including the motor was then removed from the Chassis

and set up as it is in the free body diagram above. I temporarily hot glued the motor mount and

Bracket to two heavy pieces of acrylic to serve as the chassis and Tube Chute. A spring scale

was then attached into a hold that was previously drilled into the end of the Screw axle in order

to act as a entry for a set-screw. The maximum force need to stall the motor can then calculated

utilizing the “holding” feature of the spring scale; it holds the maximum force applied to it with a

small O-ring press fit in the inside of the cylinder.

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The max force was 30 Newtons.

𝑇𝑚𝑜𝑡𝑜𝑟 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑= (43 N)*( 0.00635m)= 0.27Nm

Now that would mean I was only getting about (0.27Nm/0.34Nm) = 79% of the given stall

torque.

Comparison of analysis to performance and discussion of results:

Using the Theoretic values of the motor that are given:

I am assuming that the distance is the radius of the axle of the motor

Torque = 0.34Nm

o T=F*R

o (0.34Nm)=(F)(.0035m)

o F = 97N

Theoretical Torque:

o T = (97N)(.00635m) = .61Nm

Percent error

o (0.27Nm-0.67Nm)/(0.67Nm) = 60%

As mentioned before the maximum force indicate was used in this experiment. The force spring

scale itself is not the most accurate measuring device either, it has large increments and in not

that accurate. My max force indicator was, the o-ring, was actually a little loose, and I was

measuring the force horizontally. The o-ring may have skipped in its placement I could have

gotten a misread. Theoretically, I should have gotten a larger torque than the given torque

because I was measuring the torque through the axle of the Screw, which was 0.25 inches in

radius whereas the motor only has 0.13 inches.

I also attribute a lot of that error to the flexing of the Screw and Bracket. Even affixed to the

acrylic, the Screw and Bracket were flexing, absorbing the torque coming from the motor. The

pieces are made with 10% infill are up of PLA. The air pockets in the parts, along with the

characteristics of PLA, which are that they can take large pressures. Even more so, the glaring

source of error is the torsion in the string that ties both Screws together. There must be a

“springiness” about the string that would absorb some of the torque.

Conclusion:

Honestly, I did not even consider the string or PLA absorbing the torque as much as they did. I

hypothesized that they would act quite rigid, as that is was I saw when testing the Screws. The

Torque would sometimes snap the Screw in half, so I thought it acted as a rigid structure. What I

learned was that the torque must slowly apply force where I would not be able to accurately see

the internal effects on the PLA and string. Next time I would find equations for torsion of nylon

string and the material properties of PLA. Not only that, I would make Screws of different infills

and test their properties to better understand the physics behind it.

Overall, the robot was a VERY challenging assignment that had me working on it constantly. I

was designing constantly, but it was designing with intent. The robot speaks to this effort. The

robot might not be the scoring machine like others have, but I am very proud to say it was an

original and took a concerted effort to approach the competition with an elegant design.