Tuning a bat to optimize the trampoline effect

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Correlation Between Bat Performance and Hoop
Frequency
Dan Russell
Kettering University, Flint, MI
drussell_at_kettering.edu
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Bending Modes (common to all bats)
160 Hz
600 Hz
Hoop Mode (unique to hollow bats)
1500 Hz
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What is the Trampoline Effect?
Ball impacting solid bat
Ball impacting hollow bat
Movie courtesy of CE-Composites, Ottawa, CA
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Simple Model ? Trampoline Effect
mass-spring model of ball bat (racket, club)
Ball modeled as a non-linear, damped mass-spring
system with initial velocity
Bat modeled as a linear, damped mass-spring
system initially at rest and fixed to rigid
foundation
Set bat stiffness s2 s2 / m2 w2bat ? Hoop
frequency of barrel
Solve the coupled equations of motion numerically
Determine BBCOR v1out / v1in for a given bat
stiffness s2
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Simple Model ? Trampoline Effect
ball parameters ? softball
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Hoop Frequency Barrel Construction
34-inch slow-pitch softball bats bending and hoop
frequencies extracted from modal analysis
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Hoop Frequency Performance
ASA era study Slow-pitch Softball Bats
ASTM F2219 Cannon fires ball at 110mph towards
stationary (pivoted) bat Batted-Ball Speed
calculated from vout/vin, MOI, impact location
Wood
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Hoop Frequency Performance
Crisco Greenwald Batting Cage Study 19 players
(HS through minor league) pitched balls (66mph)
6 baseball bat models (several of
each) BBCOR values extracted by Alan Nathan
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Hoop Frequency Performance
Could hoop frequency be used to detect
illegally altered bats?
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Portable Pendulum Test
Concept Use a very heavy, very stiff ball to
impact bat barrel. Measure contact time between
ball and bat. Contact time determined by
mass of ball stiffness of bat
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Portable Pendulum Test
Direct correlation between contact time hoop
frequency
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Portable Pendulum Test
ASA era study Slow-pitch Softball Bats
ASTM F2219 Cannon fires ball at 110mph towards
stationary (pivoted) bat Batted-Ball Speed
calculated from vout/vin, MOI, impact location
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Portable Pendulum Test
Altered bats (barrel compression test) robot
swings bat at 60mph towards stationary ball
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Future Work
Portable Pendulum Tester
Digital readout
Swing bat against stationary ball include
mass/MOI properties of bat
Scan along barrel
Further correlation of data with measured
performance ?Need additional bats (with
performance data) ?Need some funding (?3,000)