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.[1] 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).
ดูหลักการทำงานได้ที่ >> http://blog.first4magnets.com/what-is-a-homopolar-motor-and-how-does-one-work/