Nick is correct, these are not shifting gearboxes. Our team strives for simple, and I think this drivetrain may be our go to for flat floor games in the future.
Our fall practice drive train used the Single Speed, Single Reduction Gearboxes from Vex:
Our gearbox plates are essentially the same thing except instead of sheet metal we went with 1/4" waterjet plate. The gearboxes have a mount for encoders similar to the Vex design and mount to both the drive rails and bumper rails. We are running a 6 motor drive train for the first time with 4 CIMs and 2 Mini-CIMs.
A big thanks to
558 for the inspiration on this design.