Basic principle of DC motor

The DC motor works on the principle that the current-carrying conductor will be affected by electromagnetic force in the magnetic field. The stator winding is fed with a DC excitation current to generate an excitation magnetic field; the main circuit introduces a DC power supply, which is transmitted to the commutator through the brush, and then the commutator converts this DC power into an alternating current and passes it into the armature winding to generate an armature magnetic field. The armature magnetic field and the excitation magnetic field form an air gap magnetic field. The armature winding cuts the synthesized air gap magnetic field to generate an electromagnetic torque to cause the rotor to rotate. This is the basic working principle of a DC motor.

The two-pole DC motor model consists of the main magnetic pole (excitation coil), armature (armature coil), brush and commutator. A pair of DC-excited static main magnetic poles N and S are installed on the stator, and the main magnetic poles are generated by the magnetic field of the excitation coil; the rotor is equipped with an armature core and an armature winding. The armature current is generated by an external DC power supply, and there is an air gap between the stator and the rotor. The head and the end of the armature coil are respectively connected to two arc-shaped commutator segments, and the commutator segments are insulated from each other. The whole composed of commutator segments is called a commutator. The commutator is fixed on the shaft and is insulated from the shaft. A pair of fixed brushes are placed on the commutator segments. When the armature rotates, the armature coil contacts the external circuit through the commutator segments and brushes, and an external DC power supply is introduced.

When the DC motor is running, the DC power supply is connected between the two brushes. The direction of the current is: the current on the effective side of the N level is always in one direction, and the current on the effective side of the S level is always in another direction. The electromagnetic force on both sides is in the same direction, so the armature rotates. When the effective side of the coil turns from the N level below (S level above) to the S level above (N pole below), the current direction changes at the same time due to the commutator segments, while the direction of the electromagnetic force remains unchanged, so that the armature is subjected to an electromagnetic torque with a constant direction. The armature of the DC motor is composed of multiple coils, so the electromagnetic torque generated by the coil is relatively uniform and there will not be too much pulsation, so the motor can run continuously and smoothly.