1. Kettering University, Flint, MI
Correlation Between
Bat Performance
and Hoop Frequency
Dan Russell
Kettering University, Flint, MI
Dan Russell “Hoop Frequency & Bat Performance” SGMA Baseball & Softball Council Fall Meeting Page 1

2. Bending Modes (common to all bats)
160 Hz
600 Hz
Hoop Mode (unique to hollow bats)
1500 Hz
Dan Russell “Hoop Frequency & Bat Performance” SGMA Baseball & Softball Council Fall Meeting Page 2

3. What is the Trampoline Effect?
Ball impacting solid bat
Ball impacting hollow bat
Movie courtesy of
CE-Composites,
Ottawa, CA
Dan Russell “Hoop Frequency & Bat Performance” SGMA Baseball & Softball Council Fall Meeting Page 3

4. 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
hysteresis
force
compression
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
Dan Russell “Hoop Frequency & Bat Performance” SGMA Baseball & Softball Council Fall Meeting Page 4

5. (energy lost)bat < (energy lost)ball
Simple Model  Trampoline Effect
Optimal Bat
hoop frequency
tuned for maximum
trampoline effect
ball parameters  softball
Elastic Bat
bat deforms,
ball deforms less
(energy lost)bat < (energy lost)ball
Very Stiff Bat
ball deforms more,
energy lost
Soft Bat
ball does not rebound
Dan Russell “Hoop Frequency & Bat Performance” SGMA Baseball & Softball Council Fall Meeting Page 5

6. Hoop Frequency & Barrel Construction
34-inch slow-pitch softball bats
bending and hoop frequencies extracted from modal analysis
Dan Russell “Hoop Frequency & Bat Performance” SGMA Baseball & Softball Council Fall Meeting Page 6

7. 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
Dan Russell “Hoop Frequency & Bat Performance” SGMA Baseball & Softball Council Fall Meeting Page 7

8. Hoop Frequency & Performance
Crisco & Greenwald Batting Cage Study
19 players (HS through minor league)
pitched balls (66mph) baseball bat models (several of each)
BBCOR values extracted by Alan Nathan
Dan Russell “Hoop Frequency & Bat Performance” SGMA Baseball & Softball Council Fall Meeting Page 8

9. Hoop Frequency & Performance
Could hoop frequency be used to detect
illegally altered bats?
Dan Russell “Hoop Frequency & Bat Performance” SGMA Baseball & Softball Council Fall Meeting Page 9

10. 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
Dan Russell “Hoop Frequency & Bat Performance” SGMA Baseball & Softball Council Fall Meeting Page 10

11. Portable Pendulum Test
Direct correlation between contact time & hoop frequency
Dan Russell “Hoop Frequency & Bat Performance” SGMA Baseball & Softball Council Fall Meeting Page 11

12. 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
Dan Russell “Hoop Frequency & Bat Performance” SGMA Baseball & Softball Council Fall Meeting Page 12

13. Portable Pendulum Test
Altered bats (barrel compression test)
robot swings bat at 60mph towards stationary ball
Dan Russell “Hoop Frequency & Bat Performance” SGMA Baseball & Softball Council Fall Meeting Page 13

14. 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)
Dan Russell “Hoop Frequency & Bat Performance” SGMA Baseball & Softball Council Fall Meeting Page 14