Calculating the Swing Weight of a Bat: Getting Pendulum Period
To calculate the swing weight of a bat you need to time the pendulum period. Below I took the 2013 Easton XL3 2 5/8 barrel and 30 inches with a drop 9 and, as an example, measured its swing weight.
I measured 10 full pendulum periods of the XL3. I did this 5 times on my iphone’s stop watch. I recorded the times as follows:
1st ten cycles: 13.23
2nd ten cycles: 13.09
3rd ten cycles: 13.35
4th ten cycles: 13.31
5th ten cycles: 13.25
I threw out the “2nd 10 cycles”. That number is further away than the rest and I suspect I hit the stop a fraction before the bat reached the extreme of the pendulum swing.
I added the remaining four numbers from the 1st, 3rd, 4th and 5th cycles: 13.23 + 13.35 + 13.31 + 13.25 = 53.14
Those numbers represented 40 pendulum swings. I divided that number (53.14) by 40 to get the XL3s Period Pendulum number for the Calculator.
53.14/40 cycles = 1.33
Pendulum Period for the XL3 = 1.33
Now I take that number and plug it into the swing weight calculator. Make sure you fill out each of the other requested items and press calculate. This will generate the swing weight (or moment of inertia) at the center of mass, six inches from the knob and at the knob.