A stepper motor consists of three main components: step angle (which relates to the number of phases), static torque, and current. Once these three components are determined, the model number of the stepper motor is determined.
1. Selection of step angle
The step angle of a motor depends on the accuracy requirements of the load. It involves converting the minimum resolution (equivalent) of the load onto the motor shaft, determining how many angles the motor should travel for each equivalent (including deceleration). The step angle of the motor should be equal to or less than this angle. Currently, step angles for stepper motors on the market are generally 0.36 degrees/0.72 degrees (five-phase motors), 0.9 degrees/1.8 degrees (two- and four-phase motors), and 1.5 degrees/3 degrees (three-phase motors), etc.
2. Selection of static moment
The dynamic torque of a stepper motor is difficult to determine immediately; we usually start by determining the motor's static torque. The selection of static torque is based on the load on the motor, which can be divided into two types: inertial load and frictional load. A single inertial load or a single frictional load does not exist. During direct starting (generally from low speed), both types of load must be considered; during acceleration starting, primarily the inertial load is considered; and during constant speed operation, only the frictional load needs to be considered. Generally, the static torque should be 2-3 times that of the frictional load. Once the static torque is selected, the motor's frame and length (geometric dimensions) can be determined.
3. Current Selection
Motors with the same static torque can have very different operating characteristics due to differences in current parameters. The motor current can be determined by referring to the torque-frequency characteristic curve (with reference to the drive power supply and drive voltage).
