[Chris Endres]

Ball shifters are quite interesting. There is a primary drive chamber, which holds balls (usually three on each level) at different heights. Those balls, when forced outward, engage the gear which is at the same level as the balls. The balls are forced outward by the piston plunger, some use servos, but VEXPro uses .5" throw pneumatic piston. Anyways, the plunger is either engaging the top gear or bottom, when the plunger shifts, it allows the balls from the previously driven gear to recede into the main drive chamber. Then the second gear is engaged by the plunger forcing the balls outward into the gear's pockets for the balls. This system makes sure that the two gears are powered at the same time, and it is a bit more complicated than dog shifters (but not by much). A good way to really see how they work is by opening the shifters up and move the plunger up and down (just watch out because the balls will fall out without a gear holding them in).

Overall, the drive shaft is powered through three little balls (yeah, weird that all of your robot's motion is in the hands of a few little ball, but it definitely works!). The main drive chamber is then connected to an output shaft, in VEXPro's case, a .5" hex output.

I'm sure there is a better way to word and name everything, but this is how I know they work. You can also look at CAD designs of custom shifters as well as VEXPro's model, you can see the geometry of the drive chamber/shaft, plunger, balls, and gears.