[Rick TYler]

Having played with models of several approaches, the one that works best is to use a single-ball channel of some kind: either ramps or a spiral. In Top Gun the balls never have a chance to jam. During their short stay in the robot the balls are always lined up on tracks, either dropping via gravity or rising on pressure belts. If you don't ever let balls get side-by-side, you won't ever have to worry about them jamming up.

In bulk material operations, stirring mechanisms are sometimes used to prevent granular stuff from plugging up chutes and outlets. We didn't go this route so I don't have anything to add from experience, but it seems to me that a short "stir stick" attached to the F-P motor with its low-speed, high-torque transmission intact might be just the thing. If you are using pneumatics, a short piston pushing upwards on a "thing" might jostle the balls when they jam.