Gearbox incorporated into frame.

[RogerR]

well, our 2004 robot was inspired by 25's evil machine.

originally, it had 4 motors (2 drill, 2 CIM) with the drills geared to run in the same direction. the drill gearboxes had mounting holes, output shaft, output gear, and output speed identical to that of the CIMs, so the 2 motors could be switched at will. it was driven by solid steel gears directly from the motors to the wheels (no chains, belts, etc.) it used (6) 8.5"x2" beadlok wheels modified to climb the steps, with the center wheel dropped 1/10". it was geared for 16 fps, and achieved about 15~15.5 fps (according to 494's dynometer). it was extraordinarily maneuverable, but because of weight concerns, the drills where removed, so over-all power was somewhat lacking.

the wheel wells where made from 1/4" thick Al plate machined on a CNC mill, and connected using 1/4-20 bolts and aluminum stand-offs. the wheel wells where connected to each other (and the spine plate) by 0.5"x1.00" Al bars on the bottom and supported by (3) 1.75" ENC tubes on the front and back. while the body had the ability to flex a little and roll with the punches(more so after some of the ENC tubes were removed) the wheel wells construction kept them stiff and rigid and we never had any problems with mis-alignment.
this drive-train was heavy, but extremely robust, maneuverable, efficient, and fast.