Baseball & softball bats - Outline
• Brief history of bat development
• Rules on baseball and softball bats
• Rigid body properties
– Mass
– Moment of inertia
– Center of percussion
• Elastic properties
– Longitudinal vibrational nodes and modes
• During impact
• During swing (diving board effect)
• Coefficient of restitution (trampoline effect)
• Is a very rigid bat or a very flexible bat more effective?
• What and where is the “sweet spot”
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Biomechanics Lab
Brief History of Bat Development:
In the Beginning
• Began with basically a
stick around 1830
• In 1850’s, handle and
barrel were emerging
• Around 1900,
modern-day
shape had
evolved
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Biomechanics Lab
History of Bat Dev: Late Wood Era
• From the early 1900’s until ~1970, the wood bat
was used exclusively with minor design changes
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History of Bat Dev: Aluminum Era
• Aluminum bats first appeared
around 1970
• Since 1980 materials with
higher strength/mass ratios
have emerged
• The plethora of recent
innovations are causing concern
by softball & baseball governing
bodies
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Biomechanics Lab
Latest Developments
• During the past three years (2002-2005) composite bats have
emerged, making them even more lively and durable, and spawning
more rule changes
• This bat has a composite insert
to connect handle and barrel to
make it super flexible
• This bat has a composite
handle and metal barrel,
and is super flexible
• The hottest bat on the market today – it is all composite materials
and it is illegal
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Biomechanics Lab
Latest
Development
in 2006:
Nanotechnology
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Nanotechnology,
cont’d
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Biomechanics Lab
Bat incorporating Nanotechnology
(CNT)
• Outstanding performance for 3 reasons:
1. New CNT Carbon Nanotube technology (CNT)
2. Composite handle giving three times greater flex than aluminum
3. Sc900 Scandium alloy
4.Patented ConneXion technology acts like a hinge to provide the
most efficient energy transfer from handle to barrel.
•ASA and USSA approved
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Biomechanics Lab
Another CNT bat
•Not ASA approved, but USSA approved, thus it is hotter than previous
bat
•Addition of CNT carbon nanotube technology strengthens composite
structures
•Designed for more handle flex - two times greater than aluminum
•How do we determine if these innovations are real or bogus?
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Biomechanics Lab
Recent Softball Bat
Rule Changes
• USSSA Softball
– Upper limit on “liveness”, or
Coefficient of Restitution (COR) –
Max BPF = 1.20
• ASA Sotball2004 BBS (Batted Ball Speed) standard
–Upper limit on “liveness”, or Coefficient of Restitution (COR)
–Maximum BBS < 98 mph under these conditions
•Effective January 1, 2004: Ball COR .44, Bat speed 85 mph, pitch speed 25
mph, multiple impact locations
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Biomechanics Lab
Recent Baseball Bat Rule
Changes
• Amateur Baseball – High School and College
–
–
–
–
–
Max barrel diameter 2.625 in (.067 m)
Max length 42” for wood, 36” for nonwood
Length-weight diff(< 3 units diff.)
Max Ball Exit Speed Ratio (BESR) – 94 or 97 MPH
Rules committee is considering a MOI rule
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Biomechanics Lab
Center of Percussion (COP)
• The COP is the point where an impact does not cause a
reaction impulse at the axis, causing the axis to tend to
translate
• Distance from axis to
center of percussion (q):
q = T2g/4B2
= .248387T2
Where T = period of
oscillation
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Biomechanics Lab
Center of Percussion
• Impacts on COP do not cause an impact reaction
impulse at the axis (Noble & Eck, MSSE 1986)
• COP has a conjugate point on the handle. Each
point on the handle is associated with a different
COP on barrel. (Cross, Am J Phys 1998)
• If the conjugate point of the COP should be near
the center of the hand-bat interface (approx 6
inches from knob end), then impact reaction
forces will be minimized.
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Center of Percussion
• In most 34-in bats, COP is
approx 6 in (15 cm) from barrel
end if hitter grips bat on knob
end
• COP can be displaced predictably
by changing the weight
distribution of the bat (Noble &
Eck, Proc ISBS 1986)
• The best site for COP
displacement is in the knob end
• COP displacement can cause
some vibration-related problems
because of the node-COP
difference discussed later
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Biomechanics Lab
Center of Percussion & the sweet spot
• Earlier studies indicated that the COP is the sweet spot, the
best place to hit the ball (Bryant, RQES 1977; Noble, ISB
Proc 1983)
• The sweet spot has since been defined in terms of two
criteria:
– The most comfortable location
• The COP has a direct effect on pain/annoyance at impact (Noble, JAB 1994;
Noble)
• Fundamental vibrational node location also has a profound effect on impact
pain/annoyance (Noble, JAB 1994)
– The location for maximum post-impact ball velocity
• Determined by characteristics other than COP (Brody, Am J Phys 1986)
– e.g., bat/ball mass and bat vel/ball vel ratios
• Vibrational node locations
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Impact vibrations and annoyance
• Node of fund mode approx 17 cm (6.7 in)
from each end and 170 Hz (Cross, Am J Phys
1998)
• First harmonic is approx 530 Hz with nodes
at approx 13 cm from BE, 5 cm from COM
toward hands, and 7 cm from KE.
• Impacts on the node will not excite that
mode.
• Mode excitation increases linearly with
impact-node distance
• Thus we have a “sweet vibrations” zone
approx 13-17 cm (5-6.7 in) from BE.
– Dan Russell’s Home Page
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Biomechanics Lab
Vibrations, COP & Impact Annoyance
• Node-COP distance is determinant of bat
preference (Noble & Dzewaltowski, Tech
Report to Easton Aluminum1994)
• Impact annoyance is least at a point between
node of fundamental & COP (Noble &
Walker Proc ISBS, 1994)
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Biomechanics Lab
Bat Vibrations During Swing
• Manufacturer’s are
claiming “diving board
effect”
• This implies that bat bends
back during the swing and
“releases the stored elastic
energy at impact, as
depicted here
• Is this implication valid?
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Biomechanics Lab
Bat Flexibility Field Test
• Effects of bat handle flexibility on performance and preferences
• First, a controlled blind field test involving 6 different bat
flexibilities with 32 elite softball players was funded by a bat
manufacturer
• Results indicated that these hyper-flexible bats resulted in greater
post-impact velocity and were
preferred by elite slow-pitch
hitters over stiffer bats
• An examination of bat
bending characteristics
during the swing followed
this study
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Biomechanics Lab
Bat bending during swing and impact
Bat Vibrations During Swing & Impact
4
Peak 41 ms PC
Begin Swing
233ms PC
3
Horiz Pk 38 ms PC
Strain (v)
2
1
0
0
0.1
0.2
0.3
0.4
0.5
0.6
-1
-2
-3
-4
Time (s)
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Horiz Dir
Vert Dir
Magnitude
Horiz Dir
Vert Dir
Magnitude
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0.7
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Begin swing 183 ms PC
Peak bending and peak
torque ~ 50 ms PC
Impact – bat still bent
back approx 20% of max
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Wood vs Aluminum Bats
• Estimates of post-impact ball
velocity of wood and aluminum
bat
• Aluminum bats are better
because
– COR is higher
– Length and weight are
independent
– Aluminum bats have lower
Moment of inertia
– Stiffness can be a design feature
– Node-COP location can be a
design feature
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Biomechanics Lab
Conclusions: Bat Vibrations During
Swing and Impact
• During the swing, the bat bends back and stores elastic
energy that is released during impact
• Thus, a more flexible bat would appear to be more effective
if the ball impacts at the sweet spot
• During impact, the bat behaves as a free-free body
• A stiffer bat would appear to be more effective if the ball
does not impact at the sweet spot.
• Perhaps a stiff bat is better for baseball and fast-pitch
softball and a flexible bat is better for slow-pitch softball
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Biomechanics Lab
So, Where and What is Sweet Spot?
• It is the best place on the bat to hit the ball,
considering
– Annoyance/comfort
– Post-impact ball velocity
• This location is:
– Location of minimal vibrations (approx 6.5 in from
barrel end)
– Location of COP with axis approx 6 in from knob end
(approx 6 in from barrel end)
– Preferably these two areas are close together
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Biomechanics Lab
Criteria for evaluating baseball & softball
bats
• Overall feel, grip, how does it fit your hand(s)
• Post impact ball response
– Control
– Power
• Durability
– Resistance to denting, cracking, etc. under normal playing
conditions
• Forgiveness – size of sweet spot
• Construction quality
– End cap, knob, welds, finish
• Would you buy the same bat again?
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Biomechanics Lab
Softball bat websites to check out
• Product reviews:
– http://www.batreviews.com/
– http://www.bandnsoftball.com/ (costs $50 per year)
• Where to buy bats:
– BallGloves.com
• Bat testing center:
– UMass Bat Research Center
• Physics of bats:
– Dan Russell’s Home Page
– Alan Nathan’s Home Page
Kansas State University
Biomechanics Lab