What Have We Learned from a Decade of Bat Research?
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What Have We Learned from a Decade of Bat Research?
Alan M. NathanUniversity of Illinois, [email protected]
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NCAA Trends in Home Runs
Q1: Why does aluminum outperform wood?Q2: What changed in 2011?
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“You can observe a lot by watching”---Yogi
Collision is very inefficientBat speed matters a lotBat slows down
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Quantifying “bat performance”
Batted Ball Speed (BBS) under game conditions
BBS depends on–Pitch Speed
• a little–Bat Speed
• a lot– “collision efficiency”
• joint property of ball and bat
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What determines collision efficiency?
1. Coefficient of Restitution2. Bat weight
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1. Coefficient of Restitution (COR)
“Bounciness” of ball– ~1/2 for baseball
• Bounces to ¼ of initial height
– bat matters also
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Contribution of Bat to COR:Vibrations and the Sweet Spot!
“sweet spot” outside
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Vibrations, BBCOR, and the “Sweet Spot”
Evib
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+vibrations minimizedCOR maximizedBBS maximizedbest “feel”
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distance from tip (inches)
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demo
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Vibrations, BBCOR, and the “Sweet Spot”
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Why are aluminum bats better?The trampoline effect
Net Result: BBCOR larger Better performance
demo
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2. Weight of bat
• Not the actual weight (“swing weight” or “MOI”)– Larger when weight concentrated in barrel– Larger for wood than aluminum
• Higher swing weight means more weight in barrel– Higher collision efficiency
• Higher BBS• Higher swing weight means lower bat speed
• Lower BBS• Two offsetting factors roughly cancel out
– Leaving BBCOR as primary property determining BBS
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An aside: Corking the Bat
• Corking the bat…– increases bat speed– decreases collision efficiency
• Which one “wins”?
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Aside: A curious feature• Bat struck at barrel
– Handle starts to move only after noticeable delay
– When reflected wave reaches barrel, collision is over
• Therefore, nothing on handle end matters– knob, handle, grip, …
• Batter could just as well drop bat just before impact!
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And here’s the proof:Todd Frazier’s No-Hands HR
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The New NCAA Standard• BBCOR is “surrogate” for BBS
– Since swing weight mostly doesn’t matter• Where to “draw the line”
– 0.500…just barely above wood
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Measuring BBCOR in Lab
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NCAA Trends in Home Runs
science works!~10% reduction in max BBCOR factor of ~2 reduction in HR
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Other Issues
• Dealing with composite bats–BBCOR improves with use– “Accelerated Break-In” or ABI
• Effect of ball on bat performance
The bottom line:We know much more than we did 10 yrs ago about how to characterize, measure,
regulate performance of bats
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webusers.npl.illinois.edu/~a-nathan/pob
Thanks for your attention