How to Select a Stepper Motor?
As an actuator, the stepper motor is a key component in mechatronics, widely used across various automation control systems. To select an appropriate stepper motor, it is essential to consider factors such as torque, load, current, inertia, speed, and precision. By carefully assessing these elements, you can identify the stepper motor that best fits the specific application requirements.
As shown in the table above, four factors need to be considered: torque, step angle, time constant, and price, to determine the most suitable type of stepper motor. For example, PM motors use metal sliding bearings rather than roller bearings, as seen in HB motors. When subjected to elastic loads, the allowable radial or thrust load values of metal sliding bearings can easily fail if belts are used for load transfer or ball screws are used for torque transmission. Additionally, attention should be given to the operating temperature range when using PM motors. VR stepper motors require closed-loop control when applied as servo motors, making this use case uncommon. This is because VR stepper motors are priced similarly to HB stepper motors but offer only half the resolution, lower efficiency than permanent magnet motors, and weaker transient characteristics. HB stepper motors provide high torque and resolution, making them well-suited for positioning tasks or low-speed operation, though they are prone to issues with vibration and noise. 
1. Select the type of stepper motor (PM, VR, HB)
Stepper motors can be broadly categorized into three types based on rotor structure: the first is the PM stepper motors, which features a stator made of sheet metal claw poles and cylindrical coils, along with a permanent ferrite magnet; the second is the VR stepper motor, which does not include permanent magnets in the rotor; and the third is the HB stepper motor, which consists of a rotor with a magnet positioned between two magnetic poles. The characteristics of the three types of stepper motors are summarized in the following table:| PM | HB | VR | |
| Step Angle | 7.5°∼15°More | 1.8° More | 1.8°∼15° |
| Torque | Small | Large | Medium to Large |
| Time constant | Small to Medium | Small | Large |
| Price | Cheap | Expensive | Expensive |
2、Determine the required torque, as static torque is one of the key parameter in selecting a stepper motor.
When determining the required static torque, it is necessary to ensure that the stepper motor's output torque exceeds the torque required by the load to maintain smooth system operation. Loads are typically classified as either inertial or frictional loads. In actual situations, a single inertial load or a single friction load does not exist. During direct startup, both loads types must be considered: inertial loads are mainly considered during acceleration, while friction loads become more relevant during constant speed operation. When calculating the load torque of the entire mechanical system, the motor's torque-frequency characteristics must satisfy the demands of the mechanical load, with an added margin to ensure reliable operation (typically, a safety factor of 1.3–2 is used for stepper motors). In actual operation, the load torque at various frequencies must fall within the torque-frequency characteristic curve. Generally, the greater the motor’s static torque, the higher its output torque and its capacity to handle larger loads.3. How to determine the speed of a motor?
When selecting a market available product, it is crucial to ensure that the stepper motor operates optimally at the intended speed. During the selection process, try to avoid the situation of insufficient motor power and excessive performance. So, how to select an appropriate stepper motor from a speed perspective? This requires distinguishing between three operational speed states of stepper motor: ① operation exclusively at low speeds; ② operation at high speeds above 2000rpm; ③ operation across a wide speed range, from low to high speeds. When running at low speed, stepper motors are prone to vibration and resonance. To minimize these effects, motors with small step angles should be selected, as three-phase motors generally perform better than two-phase motors in this regard. When operating at high speed, coil inductance can limit the inflow of current to the coils. Therefore, motors with higher phase current and lower inductance should be selected to enhance input power. Additionally, when selecting a driver, a high supply voltage is recommended.4. Select the installation specifications of the motor
Currently, the most widely used stepper motor mounting specifications on the market include NEMA8 (20×20mm), NEMA11 (28×28mm), NEMA14 (35×35mm), NEMA16 (39×39mm), NEMA17 (42×42mm), NEMA23 (57×57mm), NEMA34 (86×86mm), and NEMA42 (110×110mm). Generally, the larger the stepper motor's frame size, the greater its output torque. If installation space is limited and there is insufficient output torque, you can consider MOONS' powerplus hybrid stepper motors. The motor’s torque enhancement technology can increase the output torque by 25% - 40% across the entire speed range. This improvement is achieved by optimizing the magnetic circuit design, without the need to increase input voltage or current.