I've had a few people ask me how this thing will work. First, a picture:

Yeah, holy crap, OpenSCAD does colors.

So, in this image, the yellow parts are 3D printed. The light blue is a 9g servo, the purple parts are brushless outrunners designed for quadcopters, and the dark blue parts are grippy feeder things that are printed out of ninjaflex and attached to the outrunners.

The servo, and it's accompanying grippy feeder are set slightly forward of the outrunners. This servo will grab a sticker from the magazine and feed it, with the help of a semi-circular ramp, to the outrunners. From there, the motors - spinning at a very high RPM - will launch the sticker out of the barrel.

So it's pretty much a baseball pitching machine that you'd find in a batting cage.