Abstract: The motor comprises a rotor, first and second stators surrounding the rotor and a common exciting coil for the stators. The rotor is provided with a plurality of spaced pole pairs of alternate polarities of an odd number equal to or larger than 5. The first and second stators are respectively provided with semicircular portions which face each other and the centers of these semicircular portions are displaced from the axis of rotation of the rotor such that the semicircular portions will be point symmetrical with respect to the axis of rotation. Main pole pieces are provided for respective semicircular portions at the adjacent portions thereof and interpole pieces are located adjacent the main pole pieces which are located closest to the rotor. Notches are formed between adjacent main and interpole pieces.

Abstract: A miniature DC motor is connected to a DC source through a PNP type driving transistor. The back electromotive force of the motor which is proportional to the speed is applied to the base electrode of an NPN type control transistor through a variable resistor and the output of the control transistor is applied to the base electrode of the driving transistor through an NPN type amplifier transistor. A capacitor is connected between the base and emitter electrodes of the control transistor for smoothing the voltage applied to the base electrode of the control transistor. The sensitivity of the speed control system can be improved by connecting a Zener diode in the input circuit to the control transistor. Further the effect of the variation in the ambient temperature can be compensated for by using a thermister.