1. NCAA Research Committee June 13, 2001 Page 1 Baseball and Bat Performance Standards Alan M. Nathan Department of Physics University of Illinois at Urbana-Champaign a-nathan@uiuc.edu NCAA Research Committee Omaha, NE June 13, 2001

2. NCAA Research Committee June 13, 2001 Page 2 Outline l Introduction l General Principles l Current NCAA and ASTM Procedures l A New Proposal l Need for Additional Research l Summary/Conclusions

3. NCAA Research Committee June 13, 2001 Page 3 Introduction l The main issue: Yhow to devise laboratory tests to predict field performance l The approach: Y Study problem with model for ball-bat collision Y Model constrained by âphysics principles âdata âintelligent guessing Y Compare with available data

4. NCAA Research Committee June 13, 2001 Page 4 General Principles l Lab: Given v ball, v bat Ymeasure v f Ydetermine e A l Field: Given v ball, v bat, e A Ypredict v f v ball v bat vfvf e A = “collision efficiency” = BESR-1/2

5. NCAA Research Committee June 13, 2001 Page 5 Properties of e A v ball e A v ball l For bat initially at rest… Ye A = v f /v ball YBESR = v f /v ball + 1/2 l -1  e A  +1 Yat “sweet spot”, e A  0.2 (BESR  0.7) l v bat much more important than v ball

6. NCAA Research Committee June 13, 2001 Page 6 Properties of e A (or BESR) l It depends on... Yinertial properties (m ball, M bat, CM, MOI, impact point) YCOR of ball+bat âimpact point âv rel = v ball + v bat s but weakly l It does not depend on... Yv ball or v bat individually âonly v rel Ysupport on knob end âfree, clamped, pivoted, hand-held v ball v bat vfvf

7. NCAA Research Committee June 13, 2001 Page 7 Typical Example 34”/31 oz wood bat v ball = 90 mph  knob = 45 rad/s Conclusions: location of v f,MAX depends on * the bat (e A ) * the swing (v bat ) COP not relevant

8. NCAA Research Committee June 13, 2001 Page 8 What Does e A Depend On? = + r  bat recoil factor (inertial properties) e  ball-bat COR  0.5 = BPF e 0 e 0  ball-wall COR.. CM. b Free pivot. x. Pivoted

9. NCAA Research Committee June 13, 2001 Page 9 Example: Free Wood Bat

10. NCAA Research Committee June 13, 2001 Page 10 Free vs. Pivoted conclusions: e A ~ independent of knob end (support, mass, …) e (or BPF) not! should be tested experimentally

11. NCAA Research Committee June 13, 2001 Page 11 BPF vs. BESR vs. v f

12. NCAA Research Committee June 13, 2001 Page 12 Dot is COP Simulations of Aluminum Bats (34”, 31 oz)

13. NCAA Research Committee June 13, 2001 Page 13 Dependence on Impact Speed NOTE: effect mainly due to ball-wall COR (e 0 )

14. NCAA Research Committee June 13, 2001 Page 14 Review of Current NCAA Procedure l Standard swing: Yv ball = 70 mph v bat = 66 mph @ z=6” Yv rel = 136 mph l BHM swings bat l Measure v f and infer BESR l Require v f,max  97 mph Ye A,max  0.228 YBESR  0.728

15. NCAA Research Committee June 13, 2001 Page 15 Good Features of NCAA Procedure l Use of BESR (e A ) as performance metric Y better than BPF as predictor pf performance l Metric applied at optimum impact point Y not at some arbitrary point (COP, …) l v rel = 136 mph approximates game conditions Y far better than old ASTM method Y although 160 mph is better

16. NCAA Research Committee June 13, 2001 Page 16 Possible Problems l Problems of principle Ynot subjected to scientific scrutiny â “peer review” Yhigh torque of BHM may excite vibrations in bat l Problems of procedure Ynormalization of e A to bat speed Ycorrection for non-standard ball COR

17. NCAA Research Committee June 13, 2001 Page 17 BHM Swing vs. Batter Swing l Much higher torque with BHM Y wood bats break Y possible excitation of “diving board mode” â 15 Hz â very rough estimate s  v=  3 mph Y more study needed âmeasure vibration âcross check with other techniques

18. NCAA Research Committee June 13, 2001 Page 18 Problem with v bat Normalization must use v bat at actual impact point should not use v bat at z=6” * unless impact point is there example: suppose v f,max at z=7” or 5” and e A =0.220 * inferred e A =0.193 @ 7” and 0.247 @ 5” * this is a significant error (but easily fixed)  4.3 mph in a 90+70 collision

19. NCAA Research Committee June 13, 2001 Page 19 Problem with COR Correction l For a given ball, measure v f in 70+68 (138 mph) collision with standard bat at z=6” Yr sb =0.2278; if v f =94 mph  e 0,sb =0.459 (@125 mph) Yx  v f - 94 l For bat being tested with this ball, adjust e A Y  e A = x/v rel (should this be -x/v rel ?) l This is at best an approximation

20. NCAA Research Committee June 13, 2001 Page 20 Better COR Correction infer e 0 of ball with standard bat (using r sb ) measure e A of same ball with bat under test use r to infer e scale e by e 0,sb /e 0 used scaled e and r to recompute e A NOTE: -even this procedure is approximate -need experiments to check consistency

21. NCAA Research Committee June 13, 2001 Page 21 Review of Proposed ASTM Procedure l Project ball on stationary bat at 140 mph Y bat pivot point is 6” from knob l Measure v ball and v f for impact at COP l Use measured ball-wall COR e 0 and measured inertial properties of bat r to infer BPF l Use BPF as metric/predictor of performance

22. NCAA Research Committee June 13, 2001 Page 22 Comments on ASTM Procedure l The Good: Ycompletely transparent procedure that is easily checked by any interested observer Ydoes not attempt to measure speed of struck bat, unlike old ASTM procedure Yv rel approximates game conditions Ymeasures ball-wall COR with same apparatus l The Bad: Yuse of BPF as metric (e A is better) Yrestriction to measurements at COP

23. NCAA Research Committee June 13, 2001 Page 23 Proposed New Procedure l Use the best features of the current NCAA and the proposed ASTM procedures Yfire ball at stationary bat at 150 mph âeliminates possible complications of BHM âmakes entire process easily understood by all Ymeasure v ball and v f to get e A = v f /v ball âmeasure over broad enough range to cover v f,max âneed to define standard conditions Ycorrect e A for ball-wall COR âneed to measure ball-wall COR s at what velocity? More on this later. âneed to measure inertial properties of bat (r)

24. NCAA Research Committee June 13, 2001 Page 24 Proposed New Procedure Yuse e A and standard swing to predict v f,max Yregulate size of v f,max

25. NCAA Research Committee June 13, 2001 Page 25 z x Crisco/Greenwald Batting Cage Study Z 0.8” X 3”  45 rad/s v bat vs. z The Standard Swing  70 mph @ 28”

26. NCAA Research Committee June 13, 2001 Page 26 Standard Conditions v ball = 90 mph  knob = 45 rad/s  v rel = 160 mph @ z=6”

27. NCAA Research Committee June 13, 2001 Page 27 Standard Conditions e 0 = 0.46 Need ball-wall COR at appropriate speed If ball-bat collision is at v rel *ball-wall collision should be at same center-of-mass energy *150 mph  ~134 mph Should be checked experimentally

28. NCAA Research Committee June 13, 2001 Page 28 Crisco/Greenwald Batting Cage vs. Lansmont Laboratory

29. NCAA Research Committee June 13, 2001 Page 29 Lansmont Measurements vs. Calculations

30. NCAA Research Committee June 13, 2001 Page 30 Crisco/Greenwald Batting Cage vs. Calculations

31. NCAA Research Committee June 13, 2001 Page 31   I -n knob n=0  constant bat speed n=0.5  constant bat energy data  n=0.31  0.04 constant “bat+batter” energy, with I batter  10 4 oz-in 2  v(6”) = 1.2 x 10 -3 mph/oz-in 2 (  v f =1.5  0.3 mph) Crisco/Greenwald Batting Cage Study: bat speed versus MOI

32. NCAA Research Committee June 13, 2001 Page 32 Areas for more Experiments l More extensive wood-aluminum comparisons l BHM vs. stationary vs. field comparisons l COR: flat vs. cylindrical l Collision time vs. v rel l COR vs. v rel (recoil effect) l v bat vs. M, MOI, z CM, … l COR correction to e A l e A for free vs pivoted bat l off-axis effects

33. NCAA Research Committee June 13, 2001 Page 33 Summary of Important Points l Much of the physics of ball-bat collision well understood Ybasic principles Ymodels constrained by good data l This understanding can be applied to the issue of bat and ball standards l Laboratory measurements can predict field performance l More research needed in some areas