[Richard Wallace]

Seeing the teacher's response, I now think Billfred is right. And the advice that he and kjhobin gave above is the best -- keep the concept simple.

Since greg544 confirmed via PM that the DCM-104 motor his daughter received looks the same as the one linked in my earlier post, it appears that one challenge may be getting the right wheel speed. The machine will be small and light relative to FRC robots, and so won't need huge pushing power; however, for controllability it will require some reduction of the motor RPM to get a usable wheel RPM.

Feeding the DCM-104 directly (through a switch) from the battery charger supply will result in about 20,000 RPM free speed. Since the track boundaries are 1.5" PVC pipe and the game objects (scoring switches) are 2" off the floor, wheel diameter will be small -- let's assume 2 inches, but 1.5" would also work. A 2 inch wheel mounted directly on the motor shaft would translate at about 175 ft/sec or 120 MPH -- clearly too fast to control.

One way to gear down to a controllable speed would be to fit each DCM-104 motor with a gearbox similar to this one from BaneBots; however, at $38.95 each these would consume most of the $100 project budget.

The competition rules don't allow pre-engineered kits, or specially modified gearboxes, or inappropriate outside assistance. Still there should be some realistic way to get the wheel speed right. Maybe some VEX components would be allowed, if they are considered "parts" rather than a "pre-engineered kit"?