What is the working principle of a DC motor
A ring-shaped permanent magnet is fixed inside the DC motor, and the current generates ampere force through the coil on the rotor. When the coil on the rotor is parallel to the magnetic field, the direction of the magnetic field will continue to change when it is rotated. Therefore, the brush at the end of the rotor will change. The pieces alternately contact, so that the direction of the current on the coil also changes, and the direction of the generated Lorentz force does not change, so the motor can keep rotating in one direction.
The working principle of the DC generator is the principle that the alternating electromotive force induced in the armature coil is changed to a direct current electromotive force by the commutator in conjunction with the commutation of the brushes. The direction of the induced electromotive force is determined by the right-hand rule (the magnetic induction line points to the palm of the hand, the thumb points to the direction of the conductor's movement, and the directions of the other four fingers are the directions of the induced electromotive force in the conductor).
The direction of the force on the conductor is determined by the left-hand rule. This pair of electromagnetic forces forms a torque that acts on the armature. This torque is called electromagnetic torque in the rotating electrical machine. The direction of the torque is counterclockwise in an attempt to rotate the armature counterclockwise. If this electromagnetic torque can overcome the resistive torque on the armature (such as the drag torque caused by friction and other load torques), the armature can rotate in a counterclockwise direction.