Measuring the Spin Rate and Spin Angle of a Softball

Jeremy Bartels

Bryan Yoder

Advisor: Kevin Robinson

The Project

• Project Definition: The purpose of this project is to design a device that is capable of measuring both the spin rate and the spin angle of a softball.

Pitching Demonstration

The Market

• High School, College, Professional, Olympic Players and Coaches

• Portable device that can be used “out on the field”

Objectives:

• By the end of the term we intend to have designed and built a portable device that is capable of measuring the:A) Spin rate of the softballB) Angle of spin of the softball

Draft Plan

• Develop understanding of physics behind softball motion

• Establish ballpark specifications on softball spin velocity to explore design possibilities

• Investigate data transfer methods

• Design a suitable monitor

Action Plan

• Study other examples where successful measurement of rotational velocity has been accomplished

• Evaluate and decide upon optimal measurement technique

Feasibility

• Internal vs. External device

• Internal: Data recovery/acquisition, ball modifications

• External: Placement of device, ball modifications

External device met criteria

• Make as few modifications as possible• Keep center of mass the same• Keep area around laces the same

• No transmitter needed to recover data

External mat will see reflectors on ball

• Will use a mat with PIN diode detectors to “see” ball

• Reflectors on ball will allow for angle and rate determination

PIN Diodes pick up reflection

• Use PIN diodes to pick up the reflected light off of the ball

• Rotation and angle of ball can be determined by sequence of reflectors

Data for Mat Sizespin rate for curve ball:33 rev/sspin rate for fast ball: 25 rev/s

dist from mound to home: 40ft

curve ballmph ft/s time to home revs to home feet per revmat length for 5 revs 3 revs 2 revs50 73.3 0.5 18.0 2.2 11.1 6.7 4.455 80.7 0.5 16.4 2.4 12.2 7.3 4.960 88.0 0.5 15.0 2.7 13.3 8.0 5.365 95.3 0.4 13.8 2.9 14.4 8.7 5.870 102.7 0.4 12.9 3.1 15.6 9.3 6.275 110.0 0.4 12.0 3.3 16.7 10.0 6.780 117.3 0.3 11.3 3.6 17.8 10.7 7.185 124.7 0.3 10.6 3.8 18.9 11.3 7.690 132.0 0.3 10.0 4.0 20.0 12.0 8.0

By nyquist theorem sample at at least two times the spin frequency

the min feet per rev is 2.2, therefore, place sensors at least every 1.1 feet.

2X 5X 10X1.1 0.44 0.22

for a mat length of 8 feet, the number of sensor lines is:

2X 5X 10X7.27 18.18 36.36

Number of markers on ball per sequence 19

Diameter of Marker

0.631579 in

Area of Marker0.3132

89 in2

Surface area of the ball,45.836

66 in2

Number of Markers on the ball

146.308

Sequence probabilities

Total number of sequences 2779.8

Probability of any sequence 0.0053

Probability of not happening 0.9947

Probability of happening once 0

Probablility of happening twice 0.0052

Conclusions

• Mat idea best meets the demands and wishes defined

• Technology will catch up and make device feasible

• Concept allows for expansion for higher angle resolution