Baseball and Bat Performance Standards Alan M Nathan

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 NCAA Research Committee June 13, 2001 Page

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

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 NCAA Research Committee June 13, 2001 Page 3

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

Properties of e. A l For bat initially at rest… Ye. A = vf/vball YBESR = vf/vball + 1/2 l vball e. Avball -1 e. A +1 Yat “sweet spot”, e. A 0. 2 (BESR 0. 7) l vbat much more important than vball NCAA Research Committee June 13, 2001 Page 5

Properties of e. A (or BESR) l It depends on. . . Yinertial properties (mball, Mbat, CM, MOI, impact point) YCOR of ball+bat âimpact point âvrel = vball + vbat s l vball vbat but weakly It does not depend on. . . vf Yvball or vbat individually âonly vrel Ysupport on knob end âfree, clamped, pivoted, hand-held NCAA Research Committee June 13, 2001 Page 6

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

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 . . pivot x b . . . CM Pivoted Free NCAA Research Committee June 13, 2001 Page 8

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

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

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

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

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

Review of Current NCAA Procedure l Standard swing: Yvball = 70 mph vbat = 66 mph @ z=6” Yvrel = 136 mph BHM swings bat l Measure vf and infer BESR l Require vf, max 97 mph l Ye. A, max 0. 228 YBESR 0. 728 NCAA Research Committee June 13, 2001 Page 14

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 vrel = 136 mph approximates game conditions Y far better than old ASTM method Y although 160 mph is better NCAA Research Committee June 13, 2001 Page 15

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 NCAA Research Committee June 13, 2001 Page 16

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 NCAA Research Committee June 13, 2001 Page 17

Problem with vbat Normalization • must use vbat at actual impact point • should not use vbat at z=6” * unless impact point is there • example: suppose vf, 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 NCAA Research Committee June 13, 2001 Page 18

Problem with COR Correction l For a given ball, measure vf in 70+68 (138 mph) collision with standard bat at z=6” Yrsb=0. 2278; if vf=94 mph e 0, sb=0. 459 (@125 mph) Yx vf - 94 l For bat being tested with this ball, adjust e. A Y e. A= x/vrel (should this be -x/vrel? ) l This is at best an approximation NCAA Research Committee June 13, 2001 Page 19

Better COR Correction • • • infer e 0 of ball with standard bat (using rsb) 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 NCAA Research Committee June 13, 2001 Page 20

Review of Proposed ASTM Procedure l Project ball on stationary bat at 140 mph Y bat pivot point is 6” from knob l Measure vball and vf 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 NCAA Research Committee June 13, 2001 Page 21

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 Yvrel 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 NCAA Research Committee June 13, 2001 Page 22

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 vball and vf to get e. A = vf/vball âmeasure over broad enough range to cover vf, 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) NCAA Research Committee June 13, 2001 Page 23

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

The Standard Swing X 3” Z 0. 8” 45 rad/s 70 mph @ 28” vbat vs. z z x Crisco/Greenwald Batting Cage Study NCAA Research Committee June 13, 2001 Page 25

Standard Conditions vball = 90 mph knob = 45 rad/s vrel = 160 mph @ z=6” NCAA Research Committee June 13, 2001 Page 26

Standard Conditions e 0 = 0. 46 • Need ball-wall COR at appropriate speed • If ball-bat collision is at vrel *ball-wall collision should be at same center -of-mass energy *150 mph ~134 mph • Should be checked experimentally NCAA Research Committee June 13, 2001 Page 27

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

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

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

Crisco/Greenwald Batting Cage Study: bat speed versus MOI • 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 Ibatter 104 oz-in 2 • v(6”) = 1. 2 x 10 -3 mph/oz-in 2 ( vf=1. 5 0. 3 mph) NCAA Research Committee June 13, 2001 Page 31

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

Summary of Important Points l Much of the physics of ball-bat collision well understood Ybasic principles Ymodels constrained by good data 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 l NCAA Research Committee June 13, 2001 Page 33