[Al Skierkiewicz]

Guys,
The distance from floor to top of module is nearly the same for both our designs. (BTW, we do not use a coaxial drive, opting instead for motors in the module) We have run checks of current draw on the steering motors during a pushing match and found that without the bottom bearing (ours is near the floor) the motor current skyrockets as additional side load is applied to the bearings. It is unavoidable. Obviously, different bearing types produce different frictions, your mileage may vary. Without something to limit the side movement of the module, a strong robot is likely to move the bottom of the drive module at least a 1/4" or more if the wheels are sticky. Something has to give, and with both the steering and drive running in the assembly, something may bind and momentarily fail to perform as desired.
One lost match can screw up your whole day.