How to calculate external force acting on a pendulum

[Kenny Bala]

I am doing a physics project whose purpose involves describing the physics behind a toy. The toy I have selected is a "decision maker" which is composed of a pendulum which has a magnetically charged ball on it that swings side to side, while having a force exerted on it by magnets which change the direction and momentum of the pendulum. Could anybody direct me to a resource that explains the theory behind calculating external forces acting on a swinging pendulum, or if possible, explain it in this thread? Any help would be appreciated, and for reference, the toy looks like this http://prntscr.com/5qyefo

Thank you!

 

[haruspex]

There's nothing special about a swinging pendulum when it comes to calculating the external forces. The external forces will be whatever they are, regardless of the fact that they are acting on the bob of a pendulum.
I would start by thinking about the properties the toy needs to have to produce the desired effect.
It looks like the decisions are listed around the perimeter. How would one use it to get an answer? What does that tell you about the way the forces must be arranged?