Our robot was unique this year because it was nothing *but* a drivetrain. Obviously, that helped us keep a low center of gravity.
Our ground clearance was approximately 1/8" - despite that, another robot managed to lift us off our wheels at Nationals
The motors were mounted roughly midway between the four drive wheels. Our treads occupied the entire footprint of the robot, practically. They were all driven by a common axle. The battery was actually the highest part of our robot, directly above the motors. It was, however, only 15" or so off the floor.