Robots I have built:
Quadratic: This 4 wheel drive wall follower and maze solver was built using a PCB from Peter Harrison but with my own motors and sensors.
It uses Faulhaber motors driving modified Scalexrtix Pro wheels, and visible light LEds for wall sensing. An on board Gyro can help with the turns but is quite noisy and drifts a bit.
The 4 wheel drive gives it good traction but can make turning less precise than a 2 wheel mouse as the centre of turning can move around somewhere between the two wheels on each side.
It is a good and quick non contact wall follower but I have still to sort out the accuracy of turning to make it a reliable maze solver
It took second place in the Seniors non contact wall following competition at the 2014 Techfest