Requirements are to have a maximum power to mass ratio and torque inertia ratio, high starting torque, low inertia and a wide and smooth speed range. In particular, robotic end effectors (grippers) should use motors with as small volume and mass as possible. Especially when fast response is required, servo motors must have high reliability and large short-term overload capability. Specific requirements for use: 1. Quickness; 2. Wide range of speed control; 3. Large ratio of starting torque inertia; 4. Small size, small mass, short axial dimension; 5. Can withstand harsh operating conditions, can Very frequent forward and reverse direction and acceleration and deceleration operations, and can withstand overload in a short time; 6. Control the continuity and linearity of the characteristics, with the change of the control signal, the motor speed can change continuously, sometimes also need the speed It is proportional to or approximately proportional to the control signal. At present, DC motors with high starting torque, large torque, and low inertia are widely used in industrial robots.