Is it a must to use magnets for servo motors?
Servo motor is divided into AC Synchronous and AC Asynchronous.
If it is AC synchronous motor it has to use magnet parts, the main material is Ndfeb; if it is AC asynchronous motor, that is not necessarily to use magnetic materials.
What kind of magnet of the rotor inside the servo motor? The answer is permanent magnet which means magnetic pole and magnetic field strength (H) will not to be changed permanently. The main parts is Ndfeb in the arc shape, and injection molded multi-pole ring magnet.
Why does the rotor of the servo motor not use an electromagnet instead of a permanent magnet? The answer is the electricity means cost, also electric current (I) and the room is limited, the magnetic field that can be generated is not necessarily stronger than the permanent magnet.
So servo motors whether needs to use magnets, it has to depend on motor types.