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A stepper motor is an actuator that converts electrical pulses into angular displacement; by controlling the number of pulses, the amount of angular displacement can be regulated, thereby enabling precise positioning. Under various control signals such as digital, analog, and communication signals, stepper motors are widely used in a wide range of applications involving position and speed control. Determine the required torque: Static torque is one of the main parameters for selecting a stepper motor. A stepper motor consists of three key elements: step angle, static torque, and current. Once these three key elements are determined, the model of the stepper motor is fixed. 1. Selection of the step angle: The step angle of a motor depends on the requirements regarding load precision. The minimum resolution (equivalent value) of the load is converted to the motor shaft, determining how much angle the motor should move per equivalent unit. The step angle of the motor should be equal to or less than this angle. The step angles of stepper motors available on the market are generally 0.36 degrees/0.72 degrees (for five-phase motors), 0.9 degrees/1.8 degrees (for two- and four-phase motors), and 1.5 degrees/3 degrees (for three-phase motors), among others. 2. Selection of static torque: It is difficult to determine the dynamic torque of a stepper motor right away; we usually first determine the motor’s static torque. The selection of the static torque is based on the load under which the motor operates, and this load can be divided into inertial load and frictional load. There are no single inertial loads and no single frictional loads. During direct starting (usually at low speed), both types of loads need to be taken into account; during accelerated starting, the inertial load is the main factor to consider, while during constant-speed operation only the frictional load needs to be considered. Under normal circumstances, the static torque should be within 2-3 times the friction load; once the static torque is determined, the motor’s frame and length can be fixed. 3. Selection of current: For motors with the same static torque, their operating characteristics vary greatly due to differences in current parameters. The current value for the motor can be determined by referring to the torque-frequency characteristic curve; it should be below that curve.