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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

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Baseball and Bat Performance Standards

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  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

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