Homopolar motor

A homopolar motor is a direct current electric motor with two magnetic poles, the conductors of which always cut unidirectional lines of magnetic flux by rotating a conductor around a fixed axis so that the conductor is perpendicular to a static magnetic field. The resulting force being continuous in one direction, the homopolar motor needs no commutator but still requires slip rings. The word homopolar indicates that the electrical polarity of the conductor and the magnetic field poles do not change (i.e., that it does not require commutation).

Running in reverse, the device is known as a homopolar generator and generates electricity from rotary motion.