The simplest steering machine has two driven wheels, one on each side, and no steering wheel at all. It turns by spinning the wheels at different speeds. This is differential drive, and it is used by robot vacuums, many school robots, and countless lab robots. (A small caster ball or skid at the back or front keeps the body level; it just rolls along.)

Let the left wheel move forward at speed v_L and the right wheel at speed v_R, both in metres per second measured at the point where the wheel touches the floor. Let L be the distance between the wheels, the track width, in metres.