What is the function of the ring magnet on the rotor of DC motor?

Many friends have such doubts. Why should a ring magnet be installed on the rotor of a DC motor? What kind of magnet is this? Since there is a magnet on the stator, why is there another magnet on the rotor?

Professional knowledge is answered by professionals. The magnetic ring on the right side of the rotor sends signals to the hall element, mainly to measure the motor speed and determine the rotor position and rotation direction. Most of the bonded NdFeB and injection molded magnetic rings are usually used.

If there is only one hall element, only the motor speed can be measured. The magnetic ring on the wire suppresses conducted interference, mostly ferrite!

PS: motors are divided into rotating armature type and rotating pole type. The magnet on the stator is called rotary armature type. Such motors generally require commutators and brushes. Due to the wear of commutator and brush, the service life is not as long as that of rotating magnetic pole, but the structure is simple and the production cost is low. Rotating magnetic pole type, also known as brushless motor, has complex structure, but high reliability and is not easy to be damaged. It is used in places with high requirements.

AC motors have the ability to place magnets on the rotor or on the stator. Generally, small motors place magnets on the stator, and most motors place magnets on the rotor.