The working principle of DC motors is based on the interaction of the rotating armature magnetic field and the fixed stator magnetic field. When the positive pole of the armature is attracted to the negative pole of the stator (and vice versa), a force is generated on the armature to make it rotate. Commutation is the process of converting the magnetic field in the armature winding into a constant torque in one direction, and the commutator is a device connected to the armature, which can achieve the conversion of current. The lever arm that generates torque on the armature changes with the angle of the coil (cosα). When the coil is perpendicular to the stator magnetic field, no torque is generated. This is why DC motors have multiple coils. Therefore, even if a coil is perpendicular to the magnetic field, the armature mechanism will continue to be stressed.
The basic purpose of commutation is to ensure that the torque acting on the armature is always in the same direction. The electromotive force generated in the armature is essentially AC. The commutator converts it to DC. In short, the commutator opens and closes. Coils to control which direction the electromagnetic field points. On one side of the coil, the current should always “flow away”, and on the other side, the current should always “into” flow, which ensures that the torque is always generated in the same direction, otherwise the coil will rotate 180 degrees in one direction, Then switch directions.