Posted by: tom.guerry (tom.guerry@kp.org) on Thu Jun 17 07:25:23 2010

Dan -

Cross's paper explains how what is observed in the BB swing is different from a passive/grvity driven double pendulum. Here is a model you can play around with. If you turn on the yellow tracer to see the path of the distal tip of the second pendulum, you can see how the path shortens/quickens when the pendulum had a passive running start which is similar to intentional THT at launch and prealaunch in the swing Jack describes.

http://www.maths.tcd.ie/~plynch/SwingingSpring/doublependulum.html

Another rule of the double pendulum (also knwn as rule of the flail) is that maximum tip speed will be when the two pendula line up. In the passive model, the second/distal pendulum just keeps on turning, but in the BB swing, the bat and lead forearm stay lined up.

These are the 2 things Cross emphasizes:

1- early postive couple/THT

I would go further to say that this is not only a feature of the BB swing, but is the most important control mechanism of the swing/plane matching/adjuctment,etc

2- late "negative couple" which is perhaps best described in the TGM (the golf maching/Homer Kelley) as "extensor action".