400-450mm width isn't too bad for a featherweight. A lot of them are close to that. Obviously the smaller the better, but the GR01s (and most standard drill motors) measure ~150mm from tip to tail, so to fit inside 300mm you need to have them butted right up back-to-back. This isn't too bad in theory, but stick a disc in between them and it's hard to keep the width minimal. With this sort of design however, more width makes the robot more stable/controllable.