This invention relates to a motor used in electric control mechanical speed variators characterizing that the commutator is composed of 12 commutating plates jacketed on a rotor shaft, the rotor coilis composed of 12 winding coils, the lead out thrums of them are correspondingly connected with the plates, one end of the rotor shaft is plugged into a specially set hollow hump at the bottom of theinner cavity of the shell, the other end is supported by a seal coil closely matched to the shaft hole on the cover, a pair of brushes symmetrically mounted is set in a clamp bracket and one end of which is pressed by a spring in the bracket, the other end of which leans against the plate, the clamp bracket is inserted on the insulation plates fixed to the cover by screws.