If you could get an equation of motion, that would do it ... to worry about forces in the theta direction. Here is a diagram of the pendulum at a certain instant. I have also drawn my axes ...

Modeling the Motion of a Double Pendulum A double pendulum has two ... Typically we use two angles—θ 1 and θ 2 as shown in this diagram (assuming constant length strings).

which we can use as a pendulum too. Timing those two pendulums will synchronize the swing with the body motion to produce more power and accuracy. When watching a skilled player, these motions ...