Brief summary :
This is a simple DC motor. When the coil is energized, It would generate magnetic field around the rotor, and the left side of the rotor magnet would be pushed to the right, thereby the motor starts rotating.
The motor keeps working and running relying on the inertia.
When the rotor runs to a horizontal position, the whole working process would recycle for the current converter reversed the direction of the coil, and the magnetic field generated by the coil also reversed.
When a conductor is working in a magnetic field, the electric potential E would be generated. E=Blv.
B: the magnetic flux density
L: the conductor length;
V: the relative speed of the conductor and the magnetic field. )
The positive direction: judged by the right hand rule. Potential e positive direction indicates the direction of potential increasing, and is opposite to U.
(1) Magnetic field: the S and N are a pair of static magnetic poles, which are used to generate a magnetic field, and the magnetic induction intensity is distributed along the circumference of the circle. The field winding, the smaller the generator, is made of a permanent magnet. The magnetic field of a large capacity generator is generated by a DC current through the windings on the magnetic poles. N is used to form a pole and the S pole of the winding is called the field winding, the current in the field winding is called the excitation current If.
(2) Armature winding: Between N and S poles, there is a cylindrical core able to rotate around the axis, the coil tightening around it is named as the armature winding (only one turn coil drawn), the current in the armature winding is named as armature current IA.
(3) Commutator: the commutator is composed of the semicircular which connect both ends of the armature winding.
(4) Armature: consists of core, armature winding and commutator.
Generating electromagnetic torque
The armature winding directly connects to the DC power supply by the electric brush, and the winding’s rotating shaft is closely tied to mechanical load. The current flows from the A to the armature winding, from the B to the brush. The armature current Ia and magnetic field interact with each other to produce electromagnetic force F. The electromagnetic torque T produced by the electromagnetic force makes the motor armature rotate counterclockwise.
When the armature turns to the position shown above, the AB is turning to the S, and the CD is turning to the N, then the direction of the coil’s electromagnetic torque changes, but due to the commutator rotates simultaneously, making brush A is in contact with the wire of N pole, and brush B is in contact with the wire of S pole, so that the current flow direction changes and electromagnetic torque direction remains unchanged.
The following link address shows you how does a DC motor work: