TBM

Jordan Baker

Benny Hogan

Ashim Pant

Juan Perez

Ashim Pant

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Jordan Baker

Juan Perez

Benny Hogan

2

Introduction

• Tennis is a sport that is almost impossible to play alone
• Tennis ball machines can substitute a playing partner by artificially creating a tennis shot
• Models that adequately replace a human are very expensive and cheaper models lack functionality

Problem Definition

Through the application of newly accessible technology and modern prototyping methods a fully automated tennis ball machine could be produced for a fraction of the cost of existing, equivalently functional designs.

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Design Requirements & Constraints

Requirements

• Spin control
• Velocity control
• Launch Angle
• Rotation Angle
• Feed timing variation
• Wirelessly Controllable
• Programmable

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Constraints

• Time
• Budget
• Skills and labor

Ideas & Concepts proposed

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Three-wheel design

• Different planes of spin
• Complicated and expensive

Two-wheel design

• Multiple planes of spin
• Infeasible

Stationary, Two-wheel design

• One plane spin
• Simple, cheap and feasible

Magnus effect

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References:

1. Cross, R., 1987, “Ball Trajectories; Factors Influencing the Flight of the ball,” pp. 367–374.
2. Cross, R., and Lindsey, C., 2009, “Tennis Ball Trajectories,” p. 2009.

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• The spin rate of tennis ball has a dramatic effect on it’s trajectory
• The magnus effect accounts for the force on a ball perpendicular to its velocity, proportional to its spin rate
• Drag also places a significant role in a ball’s trajectory

Exit Velocity & Spin Rate

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Reference:

1. Wójcicki, K., Puciłowski, K., and Kulesza, Z. S., 2011, “Mathematical Analysis for a New Tennis Ball Launcher,” Acta Mech. Autom., Vol. 5(No. 4), pp. 110–119.

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• The rotation of the firing wheels determines both the launch velocity and the spin rate of the ball
• Required launch velocity was a balance between motor RPM and firing wheel radius

FEA

• Minor load bearing components
• Simple simulations used to justify geometry and material
• 3/16^th, 6061 Aluminum
• Plasma cut, then welded
• Safety factors > 15

8

Stress experienced by the base

Stress on legs

Stress analysis of the wheel frame

Shafts

• Critical Location of system
• Withstanding dynamic movement
• Bending moments and Torsion coming from the tennis ball

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9

Fatigue Analysis

Combined Loadings

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(Fatigue Safety Factor)

(Langer Yield Check)

References:

1. Budynas, G. R., and Nisbett, K. J., 201AD, Mechanical Engineering Design, McGraw-Hill Education, New York.

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Fabrication

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Ball bearing

Coupler

Carbon steel shaft.

Wheel with rubber spray

Frame with shaft and bearings

Challenges

• Firing wheel spacing
• Increasing friction of the firing wheels
• Precision of bearing fit
• Secure shaft coupling
• Shaft walking
• Noise reduction
• 3D printer inaccuracies

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3D Printing

• Stereolithography
• Fused Deposition Modelling
• Some components too large for a single print
• Allowed for rapid and unique prototyping at reduced cost

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3D printed sorting ring

Sorting ring

Drive Motor housing

PVC flange

Stepper housing

Horizontal oscillation gears

Ball feeder

Electrical Components

• Three different power supplies
• Arduino controls power supply and recognises user’s input
• Components respond to the control unit and perform their function

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Voltage regulation from the power supply

Block diagram

User Control

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Final Design

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Testing & Validation

Top speed = 92 mph

Twist angle = 30 °

Launch angle = 23 °

Ball timing = 2 seconds

Battery life = 2 hours

Final Cost = $909.27

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16

Conclusion & Recommendations

• This design has made a two person sport into a one player sport.
• Elite level coaching and recreational play can be achieved using the flexibility achieved from open source programming
• No other existing market product has all these features for under $2000
• Coupling of motor shafts and drive wheels may be unnecessary
• Slightly more expensive batteries may be worth the weight savings
• Further iterations and successive prototypes should address secondary objectives such as portability and aesthetics
• Be an electrical engineer

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Acknowledgements & Demonstration

• Andy Pimentel
• Dr. Emily Hunt
• Dr. Matt Jackson
• Dr. Joshua Partheepan
• Jay McGaugh
• WT Softball team
• Trace Hansen, WT Baseball G.A.
• RCC Brass

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