How do I choose a stepper motor

Basic parameter:

Inherent Step Angle:

It represents the angle that the motor rotates for each step pulse signal sent by the control system. When the motor produces, it will have a step angle value. For example, the step angle value of H421(NEMA 17) is 1.8°. this step angle can be called the motor’s inherent step angle. But it doesn’t mean that this is the real step angle when the motor works. The real step angle is related to the drive.

Phase number:

It refers to the number of coil groups in the motor. At present, the two-phase, the three-phase, the four-phase, and the five-phase stepper motor are commonly used. Different motor phases have different steps angle. Commonly, the step angle of the two-phase motor is 0.9°/1.8°, three-phase motors are 0.75°/1.5°, five-phase motors are 0.36°/0.72°. Without using subdivision drivers, users select different phase motors to meet the application’s step angle requirement. If using subdivision drivers, the phase number is meaningless. Because of changing the subdivision number on the driver, the step angle can be changed.

Holding Torque:

It refers to the torque that the stator locks the rotor when the stepper motor is energized but not rotating. It is one of the most important parameters in stepper motors. Usually, the torque of the stepper motor at low speed is close to holding toque. Because the output torque of the stepper motor will decrease with the increase of speed, the output power will also change with the increase of speed, so the holding torque is the most important parameter to measure the stepper motor. For example, a 2N.m stepper motor is a stepper motor having a holding torque of 2N.m.

Detent Torque

It refers to the torque that the stator locks the rotor when the stepper motor is not energized. Since the rotor of the reactive stepper motor is permanent magnet material, it doesn’t have detent torque.

PS: In china, the “Detent Torque” doesn’t have a uniform translation.

The Factor of Choosing Stepper Motor:

1, Torque Selection

The holding torque of the stepper motor is close to the “power”. Of course, there is an essential difference. The structure of the stepper motor is different AC, DC motor, whose output power can change. The selection of the motor is based on the torque. (that is to say, the torque, which drives the object) Generally, if the torque is less than 0.8N.m, it is suitable to choose 20mm, 28mm, 35mm,39mm, 42mm Stepper motor; if the torque, 57mm motor is suitable. When the torque is several N.m or more, 86mm, 110mm, 130mm stepper motors should be considered.

2, Speed Selection

It is important to consider the speed of the motor. Because the output torque is inversely proportional to the speed. That is to say, the motor torque is large at low speed(a few hundred revolutions per minute), the motor torque is small at high speed(1000-9000rpm). of course, in some working conditions, the high-speed motor is required. So it is necessary to measure the coil resistance, inductance. Choosing a stepper motor with lower inductance as a high-speed motor can obtain a higher output torque. Conversely, in the requirement of low speed and high torque, it is necessary to choose inductance of a dozen or tens of mH and a larger resistance.

3, No-load Starting Frequency Selection

This is an important indicator in choosing motors. If it is required to start, stop frequently and instantaneously and the speed is around 1000rpm(or higher), then “accelerated start” should be used. If achieving high speed at the start, it is best to choose reactive or permanent motor. “empty starting frequency” of these motors is relatively high.

4, Phase Number Selection

For this aspect, many customers pay a little attention. Stepper motors with different phase numbers have different working effects. The greater the number of phases, the smaller the step angle can be made, and the vibration will be less during work. In most cases, two-phase motors are widely used. In high speed and high torque working environments, choosing three-phase motors are practical.

5, Choose according to Working Environment

Some special stepper motors can be used in some special applications such as waterproof, oil-proof. For a special purpose, choosing should be based on needs.

6, Contact with Engineers

If necessary, you should communicate with the technical engineer of the manufacture to learn if the motor you want to buy can meet your needs.