Kansas State University Biomechanics Lab Baseball & softball bats - Outline Brief history of bat development Rules on baseball and softball bats Rigid

Kansas State University Biomechanics Lab

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”


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


History of Bat Dev: Late Wood Era

• From the early 1900’s until ~1970, the wood bat was used exclusively with minor design changes


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


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


Latest Development

in 2006: Nanotechnology


Nano-technology,

cont’d


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


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?


Recent Softball BatRule 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


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


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/42

= .248387T2

Where T = period of oscillation


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.


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


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


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


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)


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?


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


Bat Vibrations During Swing & Impact

-4

-3

-2

-1

0

1

2

3

4

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Time (s)

Str

ain

(v

)

Horiz DirVert DirMagnitudeHoriz DirVert DirMagnitude

Begin Swing 233ms PC

Peak 41 ms PC

Horiz Pk 38 ms PC

Bat bending during swing and impact



Begin swing 183 ms PC

Peak bending and peak torque ~ 50 ms PC

Impact – bat still bentback approx 20% of max


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


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


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


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?


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

Documents

Kansas State University Biomechanics Lab Baseball & softball bats - Outline Brief history of bat development Rules on baseball and softball bats Rigid