Homopolar motor - Wikipedia, the free encyclopedia: 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 that is parallel to the magnetic field. The resulting EMF (Electromotive Force) being continuous in one direction, the homopolar motor needs no commutator but still requires slip rings. The name 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).
The homopolar motor is driven by the Lorentz force: as it moves through a magnetic field, the conductor is pushed through a magnetic field by opposing forces. This force induces a torque around the axis of rotation. Because the axis of rotation is parallel to the magnetic field, and the opposing magnetic fields do not change polarity, no commutation is required for the conductor to keep turning. This simplicity is achieved at the cost of not being able to have more than one coil turn, which makes this configured homopolar motor unsuited for most useful applications. Homopolar motors have advantages and disadvantages and have not been fully developed.
Like most electro-mechanical machines, a homopolar motor is reversible: if the conductor is turned mechanically, then it will operate as a homopolar generator, producing a direct current voltage between the two terminals of the conductor. The direct current produced is an effect of the homopolar nature of the design.