Electric motor

An electric motor comprises a stator and a rotor received in the stator. The stator comprises a shell. The shape of a cross section of the shell perpendicular to the rotor axis is a polygon. The shell comprises a plurality of side walls and arcuate connection portions connecting neighboring side walls. The stator comprises 2n magnets disposed in the arcuate connection portions. The magnets form 2m magnetic poles, where m, n are unequal positive integers. Optionally, m is equal to half or twice n. The permanent magnets of the motor are located in the inner angle of polygon shell. Thus the diameter of rotor can be the greater, and the power density of motor can be increased in the same volume.