Baseball and Bat Performance Standards

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

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

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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

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General Principles
eA collision efficiency BESR-1/2

• Lab Given vball , vbat
• measure vf
• determine eA
• Field Given vball , vbat , eA
• predict vf

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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

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Properties of eA(or BESR)

• It depends on...
• inertial properties (mball, Mbat, CM, MOI, impact
  point)
• COR of ballbat
• 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

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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

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What Does eA Depend On?


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Example Free Wood Bat
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Free vs. Pivoted

• conclusions
• eA independent of knob end (support, mass, )
• e (or BPF) not!
• should be tested experimentally

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BPF vs. BESR vs. vf
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Simulations of Aluminum Bats (34, 31 oz)
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Dependence on Impact Speed
NOTE effect mainly due to ball-wall COR (e0)
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Review of Current NCAA Procedure

• Standard swing
• vball 70 mph vbat 66 mph _at_ z6
• vrel 136 mph
• BHM swings bat
• Measure vf and infer BESR
• Require vf,max ? 97 mph
• eA,max ? 0.228
• BESR ? 0.728

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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

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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

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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

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Problem with vbat Normalization

• must use vbat at actual impact point
• should not use vbat at z6
• unless impact point is there
• example suppose vf,max at z7 or 5 and
  eA0.220
• inferred eA0.193 _at_ 7 and 0.247 _at_ 5
• this is a significant error (but easily fixed)
• ?4.3 mph in a 9070 collision

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Problem with COR Correction

• For a given ball, measure vf in 7068 (138 mph)
  collision with standard bat at z6
• rsb0.2278 if vf94 mph ? e0,sb0.459 (_at_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

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Better COR Correction

• infer e0 of ball with standard bat (using rsb)
• measure eA of 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
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Review of Proposed ASTM Procedure

• Project ball on stationary bat at 140 mph
• bat pivot point is 6 from knob
• Measure vball and vf for impact at COP
• Use measured ball-wall COR e0 and
• measured inertial properties of bat r to
• infer BPF
• Use BPF as metric/predictor of performance

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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

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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)

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Proposed New Procedure

• use eA and standard swing to predict vf,max
• regulate size of vf,max

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?70 mph _at_ 28
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Standard Conditions
vball 90 mph ?knob 45 rad/s ? vrel 160
mph _at_ z6
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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

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Crisco/Greenwald Batting Cage vs. Lansmont
Laboratory
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Lansmont Measurements vs. Calculations
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Crisco/Greenwald Batting Cage vs. Calculations
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Crisco/Greenwald Batting Cage Study bat speed
versus MOI

• ? ? I-n knob
• n0 ?
• constant bat speed
• n0.5 ?
• constant bat energy
• data ?
• n0.31 ? 0.04
• constant batbatter
• energy, with Ibatter?104 oz-in2
• ?v(6) 1.2 x 10-3 mph/oz-in2 (?vf1.5 ? 0.3
  mph)

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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

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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