1 / 33

Baseball and Bat Performance Standards

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. Outline. Introduction General Principles Current NCAA and ASTM Procedures A New Proposal

dara
Download Presentation

Baseball and Bat Performance Standards

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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. Outline • Introduction • General Principles • Current NCAA and ASTM Procedures • A New Proposal • Need for Additional Research • Summary/Conclusions

  3. Introduction • The main issue: • how to devise laboratory tests to predict field performance • The approach: • Study problem with model for ball-bat collision • Model constrained by • physics principles • data • intelligent guessing • Compare with available data

  4. vball vbat vf General Principles • Lab: Given vball , vbat • measure vf • determine eA • Field: Given vball , vbat , eA • predict vf eA = “collision efficiency” = BESR-1/2

  5. vball eAvball Properties of eA • For bat initially at rest… • eA = vf/vball • BESR = vf/vball + 1/2 • -1  eA  +1 • at “sweet spot”, eA  0.2 (BESR  0.7) • vbat much more important than vball

  6. vball vbat vf Properties of eA(or BESR) • It depends on... • inertial properties (mball, Mbat, CM, MOI, impact point) • COR of ball+bat • impact point • vrel = vball + vbat • but weakly • It does not depend on... • vball or vbat individually • only vrel • support on knob end • free, clamped, pivoted, hand-held

  7. Typical Example 34”/31 oz wood bat vball = 90 mph knob = 45 rad/s Conclusions: • location of vf ,MAX depends on • the bat (eA) • the swing (vbat) • COP not relevant

  8. . . . CM b . . pivot r bat recoil factor (inertial properties) e ball-bat COR  0.5 = BPF e0 e0  ball-wall COR x Pivoted Free What Does eA Depend On? = +

  9. Example: Free Wood Bat

  10. Free vs. Pivoted conclusions: • eA ~ independent of knob end (support, mass, …) • e (or BPF) not! • should be tested experimentally

  11. BPF vs. BESR vs. vf

  12. Dot is COP Simulations of Aluminum Bats (34”, 31 oz)

  13. Dependence on Impact Speed NOTE: effect mainly due to ball-wall COR (e0)

  14. Review of Current NCAA Procedure • Standard swing: • vball = 70 mph vbat = 66 mph @ z=6” • vrel = 136 mph • BHM swings bat • Measure vf and infer BESR • Require vf,max 97 mph • eA,max 0.228 • BESR  0.728

  15. Good Features of NCAA Procedure • Use of BESR (eA) as performance metric • better than BPF as predictor pf performance • Metric applied at optimum impact point • not at some arbitrary point (COP, …) • vrel = 136 mph approximates game conditions • far better than old ASTM method • although 160 mph is better

  16. Possible Problems • Problems of principle • not subjected to scientific scrutiny • “peer review” • high torque of BHM may excite vibrations in bat • Problems of procedure • normalization of eA to bat speed • correction for non-standard ball COR

  17. BHM Swing vs. Batter Swing • Much higher torque with BHM • wood bats break • possible excitation of “diving board mode” • 15 Hz • very rough estimate • v=3 mph • more study needed • measure vibration • cross check with other techniques

  18. 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 eA=0.220 • inferred eA=0.193 @ 7” and 0.247 @ 5” • this is a significant error (but easily fixed) • 4.3 mph in a 90+70 collision

  19. Problem with COR Correction • For a given ball, measure vf in 70+68 (138 mph) collision with standard bat at z=6” • rsb=0.2278; if vf=94 mph  e0,sb=0.459 (@125 mph) • x  vf - 94 • For bat being tested with this ball, adjust eA • eA= x/vrel (should this be -x/vrel?) • This is at best an approximation

  20. Better COR Correction infer e0of ball with standard bat (using rsb) measure eAof same ball with bat under test use r to infer e scale e by e0,sb/e0 used scaled e and r to recompute eA NOTE: -even this procedure is approximate -need experiments to check consistency

  21. Review of Proposed ASTM Procedure • Project ball on stationary bat at 140 mph • bat pivot point is 6” from knob • Measure vball and vffor impact at COP • Use measured ball-wall COR e0and measured inertial properties of bat rto infer BPF • Use BPF as metric/predictor of performance

  22. Comments on ASTM Procedure • The Good: • completely transparent procedure that is easily checked by any interested observer • does not attempt to measure speed of struck bat, unlike old ASTM procedure • vrel approximates game conditions • measures ball-wall COR with same apparatus • The Bad: • use of BPF as metric (eA is better) • restriction to measurements at COP

  23. Proposed New Procedure • Use the best features of the current NCAA and the proposed ASTM procedures • fire ball at stationary bat at 150 mph • eliminates possible complications of BHM • makes entire process easily understood by all • measure vball and vf to get eA = vf/vball • measure over broad enough range to cover vf,max • need to define standard conditions • correct eA for ball-wall COR • need to measure ball-wall COR • at what velocity? More on this later. • need to measure inertial properties of bat (r)

  24. Proposed New Procedure • use eA and standard swing to predict vf,max • regulate size of vf,max

  25. The Standard Swing z X 3” Z 0.8” x  45 rad/s vbat vs. z Crisco/Greenwald Batting Cage Study 70 mph @ 28”

  26. Standard Conditions vball = 90 mph knob = 45 rad/s  vrel = 160 mph @ z=6”

  27. Standard Conditionse0 = 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

  28. Crisco/Greenwald Batting Cage vs. Lansmont Laboratory

  29. Lansmont Measurements vs. Calculations

  30. Crisco/Greenwald Batting Cage vs. Calculations

  31. Crisco/Greenwald Batting Cage Study: bat speed versus MOI •   I-nknob • 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-in2 • v(6”) = 1.2 x 10-3 mph/oz-in2(vf=1.5  0.3 mph)

  32. Areas for more Experiments • More extensive wood-aluminum comparisons • BHM vs. stationary vs. field comparisons • COR: flat vs. cylindrical • Collision time vs. vrel • COR vs. vrel(recoil effect) • vbat vs. M, MOI, zCM, … • COR correction to eA • eA for free vs pivoted bat • off-axis effects

  33. Summary of Important Points • Much of the physics of ball-bat collision well understood • basic principles • models constrained by good data • This understanding can be applied to the issue of bat and ball standards • Laboratory measurements can predict field performance • More research needed in some areas

More Related