Each wheel was geared down 75:1 and was controlled by either 2 or 3 motors at all times. We had to turn off the motors from the expansion board when we wanted precision control, since their speeds don't vary. Other than the two wheels, 14 coasters dragged along the surface of the table (8 in back, 6 in front). Light-shielded shaft-encoders provided turns accurate to 5 or 10 degrees and distance to within an inch.
We designed with the four `S's in mind: Simple, Strong, Speedy, and Small. Our robot has no ball-latching mechanisms, yet it was able to reliably pitch balls into the gutter from across the table. Horizontal wheels at each of the four corners make it easy for our robot to slip along walls, using them for guidance. Distance sensor values are recorded as the robot sweeps along the back width of the table, determining whether the blue block is near or far.