Design for a printed piece to drop one marble at a time for PLTW material sorter. Connected to a servo, works very well. See it in action: https://www.youtube.com/watch?v=Ueql7RzjQGU

Updated parts, the ones called designdropper. Edited the first design to better fit the marbles and a bigger opening for the shaft. The second design can turn in a full circle to drop a marble, letting you use a motor instead of a servo.

I have included two types - one that is open on one side, mover2s, I originally thought it might work sideways. This is the one in the video. I've included one that is a little wider and is closed on both sides. the Autodesk Inventor .ipt's are there in case anyone wants to modify them.