And here's a video of it in operation:
http://www.dailymotion.com/video/x10604k_discrete-pendulum-mod-to-spinner-kit_creation
The "index" signal toggles a flip-flop, that in turn grounds the bottom of one cap, while opening another, which changes which guide leads. Hence, the direction of rotation, is determined.
... is the speed of the movement still adjustable?