How to change the speed of DC motor
The direction of dc motor rotation is related to the direction of current in the coil and the direction of magnetic induction line cut by the coil. The rotation direction of the motor can be changed by changing the direction of the coil current. The direction of the coil cutting magnetic induction line remains the same, and the rotation direction of the motor changes if the current direction in the coil is changed. The rotation speed of the motor can be changed when the current passing through the coil is changed.
According to the left hand rule, when either the direction of the armature current or the direction of the magnetic field (that is, the direction of the excitation current) is reversed. The direction of force on the armature conductor changes, and the direction of rotation of the motor changes accordingly. However, if the direction of both the armature current and the magnetic field change at the same time, the direction of rotation of the motor remains the same.