The working principle of the needle motor is to change the alternating electromotive force induced in the armature coil by the commutation function of the commutator and the brush to change the DC electromotive force when it is taken out from the brush end. The direction of the induced electromotive force is determined by the right-hand rule (the magnetic line is pointing to the palm of the hand, the thumb is pointing to the direction of movement of the conductor, and the other four fingers are pointing in the direction of the induced electromotive force in the conductor).
The direction of the force of the conductor of the pin wheel motor is determined by the left-hand rule. This pair of electromagnetic forces forms a moment acting on the armature. This torque is called electromagnetic torque in the rotating machine, and the direction of the torque is counterclockwise. Attempts to rotate the armature counterclockwise. If this electromagnetic torque can overcome the resistive torque on the armature (such as the resistive torque caused by friction and other load torque), the armature can be rotated counterclockwise.
When the needle wheel motor is used, it mainly relies on the DC operating voltage to operate the motor, and is widely used in tape recorders, video recorders, DVD players, electric shavers, hair dryers, electronic watches, toys, and the like.
The excitation winding of the pinwheel motor has no connection relationship with the armature winding, and the DC motor that is powered by the other DC power supply to the excitation winding is called a separately excited DC motor. In the figure, M represents the motor, and if it is a generator, it is represented by G. Permanent magnet DC motors can also be regarded as their excitation DC motors.