Abstract: Minaturized unipolar low power rotational speed transducers or tachometer generators are disclosed, one of which is comprised of coaxial housing and pole members of magnetic material and a permanent magnet interposed therebetween and which housing and pole member provide an annular air gap receiving the annular side wall of a rotatable cup-shaped rotor of electrically conductive material. The rotor is supported by a drivable shaft at the end of the housing corresponding to the closed end of the rotor, and a pair of brushes radially engage the rotor side wall adjacent the closed and open ends of the rotor to provide an output signal in response to driving rotation of the rotor.