A motor comprises a stator and a rotor. The stator comprises 2P poles wherein P is an integer greater than one. The rotor comprises a shaft, a rotor core and a commutator fixed to the shaft. The commutator comprises m segments where m is an even integer greater than P. Every two adjacent segments are electrically connected by a winding unit so that the rotor winding comprises m winding units with at least one of the winding units comprising P coils connected in series; and each coil of each winding unit is directly connected to a corresponding two segments.