Views: 0 Author: July Publish Time: 2026-09-23 Origin: Site
Stepper motors are widely used in automation equipment, CNC machines, printers, robotics, positioning systems, and other motion-control applications. However, achieving the expected torque, speed, and positioning performance depends not only on the motor itself, but also on proper driver matching, operating conditions, wiring configuration, and motor selection.
This guide explains the basic working principle of stepper motors, heat generation, efficiency optimization, motor and driver matching, and stepper motor selection methods.
A typical stepper motor uses a permanent-magnet rotor and a stator with multiple windings. When current flows through the stator windings, the windings generate a magnetic field that interacts with the rotor and causes it to rotate to a specific angular position.
When the stator's magnetic field changes position, the rotor follows the magnetic field and rotates accordingly.
Each electrical pulse causes the motor to move through a specific angle, known as the step angle. Therefore:
· The angular displacement is proportional to the number of input pulses.
· The motor speed is proportional to the pulse frequency.
· The rotation direction can be changed by changing the energizing sequence of the motor windings.
As a result, the position, speed, and direction of a stepper motor can be controlled by adjusting the number of pulses, pulse frequency, and phase excitation sequence.
Most electric motors contain an iron core and winding coils. The windings have electrical resistance, and when current flows through them, power is dissipated as heat.
The winding loss is generally referred to as copper loss, and it is related to resistance and the square of the current.
When the current is not a standard DC or sinusoidal waveform, additional harmonic losses can also occur.
The motor's iron core experiences hysteresis and eddy-current losses when exposed to an alternating magnetic field. These losses are affected by factors such as:
· Material
· Current
· Frequency
· Voltage
Copper loss and iron loss are ultimately manifested as heat, which affects motor efficiency.
Stepper motors generally prioritize positioning accuracy and torque output. Their operating current can be relatively high, and their current waveform contains harmonic components. Since the alternating current frequency also changes with motor speed, stepper motors commonly experience noticeable heat generation.
Although stepper motors are widely used, they cannot simply be operated like conventional DC or AC motors. A complete stepper motor system generally requires pulse signals, power drive circuitry, and a control system.
Proper use therefore involves considerations related to mechanical systems, motors, electronics, and control.
In many applications, a stepper motor may appear to have insufficient torque even when its rated specifications seem adequate. Increasing the motor size or rated current is not always necessary. The problem may instead come from improper motor selection or incorrect driver-current settings.
Proper matching between the motor and driver is therefore important for achieving the expected performance.
Most modern two-phase stepper motor drivers use a full-bridge output configuration.
For a four-wire two-phase stepper motor, setting the driver according to the motor's rated current is generally considered the appropriate configuration and can provide the expected output torque.
Many newer stepper motors use this configuration.
Earlier stepper motors were commonly available in:
· Two-phase six-wire configurations
· Two-phase eight-wire configurations
The wiring configuration affects the motor's electrical characteristics and operating performance.
A two-phase six-wire stepper motor generally has two connection methods.
The center taps are not used, and the two coils in each phase are connected in series.
This configuration provides:
· Higher holding torque
· Higher efficiency
· Lower high-speed performance
The center tap and one end of the winding are connected.
This configuration provides better high-speed performance. However, one coil section in each phase remains unused, resulting in:
· Lower holding torque
· Lower efficiency
When using a six-wire stepper motor, the driver current must therefore be considered carefully.
According to the source material, when the two-phase six-wire motor uses the series connection, the phase resistance increases and the rated operating current decreases. Simply setting the driver to the motor's marked current may therefore prevent the motor from reaching its expected output.
The recommended calculation given is:
Driver Current = Rated Motor Phase Current × 0.7
For example, if a two-phase six-wire stepper motor has a rated current of 3 A:3 A × 0.7 = 2.1 A
The driver current should therefore be set to approximately 2.1 A according to this method.
Eight-wire stepper motors also provide two common connection methods.
The two coil sections are connected in series.
According to the source material, the driver current should be set to approximately:
Rated Motor Phase Current × 0.7
This configuration produces lower heat generation but has relatively weaker high-speed performance.
The coil sections are connected in parallel.
In this configuration, the driver current is set to approximately:
Rated Motor Phase Current × 1.4
The advantages include:
· Better high-speed performance
· Higher output torque
· Improved dynamic performance
The disadvantage is higher heat generation.
A certain amount of heat is considered normal during stepper motor operation, provided the motor remains below its specified demagnetization temperature.
When using a stepper motor driver with a preset output current, proper motor selection becomes especially important.
For example, if the driver output current is 2 A, a two-phase four-wire 2 A motor can be selected.
If a two-phase six-wire motor is used, the source material gives the following calculation:
2 A ÷ 0.7 ≈ 2.9 A
Therefore, a six-wire motor with a rated phase current of approximately 2.9 A should be selected according to this method.
Proper motor-driver matching helps make better use of the available driver output and motor performance.
Selecting a stepper motor and driver should be based on the actual requirements of the mechanical system.
The main factors include:
· Required torque
· Operating speed
· Motor size
· Positioning accuracy
· Vibration requirements
· Motor current
· Driver microstepping
· Driver supply voltage
Holding torque is one of the primary parameters used when selecting a stepper motor.
For larger loads, a higher-torque motor is required. Motors with higher torque ratings generally have larger frame sizes.
When higher speed is required, a motor with suitable phase current and lower inductance should be considered.
A higher driver supply voltage can also be selected according to the motor and driver specifications.
Common stepper motor frame sizes include:
· 57 mm
· 86 mm
· 110 mm
The appropriate frame size is mainly related to the required torque.
If the application requires improved positioning performance or reduced vibration, the required microstepping level should be evaluated.
Several key parameters should be evaluated before choosing a stepper motor.
Selection Parameter | Main Consideration |
Step Angle | Determines basic positioning resolution |
Holding Torque | Determines load-driving capability |
Current | Affects motor output and operating temperature |
Speed | Determines required motor electrical characteristics |
Frame Size | Related to available torque and installation space |
Inductance | Important for high-speed performance |
Number of Phases | Influences step angle and operating characteristics |
Environment | Determines whether a specialized motor is required |
The required step angle depends on the positioning accuracy of the load.
The minimum required movement of the load should first be converted into the corresponding angular movement at the motor shaft. The motor's step angle should be equal to or smaller than this required angle.
Common step angles include:
· 0.36° / 0.72° for some five-phase motors
· 0.9° / 1.8° for two- and four-phase motors
· 1.5° / 3° for three-phase motors
Holding torque is often used as the starting point for selecting the motor size.
The load can generally be considered in terms of:
· Inertial load
· Friction load
Both should be considered during direct starting, while inertial load becomes particularly important during acceleration.
The source material gives the following approximate selection ranges:
Required Torque | Suggested Motor Frame |
Below 0.8 N·m | 20, 28, 35, 39, or 42 mm |
Around 1 N·m | 57 mm |
Several N·m or higher | 86, 110, 130 mm and larger |
The actual motor should still be selected according to the specific mechanical load and operating conditions.
Stepper motor output torque generally decreases as rotational speed increases.
At low speeds, such as several hundred RPM or lower, a stepper motor can provide relatively high torque. At higher speeds, torque decreases.
For high-speed applications, motors with lower inductance can provide better high-speed torque performance.
For applications requiring high torque at low speed, motors with higher inductance and resistance may be considered according to the required operating characteristics.
The starting frequency, also known as the no-load starting frequency, is an important parameter when selecting a stepper motor.
If an application requires frequent starting and stopping at around 1,000 RPM or higher, acceleration control is generally required.
If the motor must reach a high speed immediately after starting, the source material recommends considering reactive or permanent-magnet stepper motors with a higher no-load starting frequency.
The number of motor phases also affects operating performance.
Motors with more phases can achieve smaller step angles and generally lower vibration.
Two-phase stepper motors are widely used in many applications.
For applications requiring high speed and high torque, three-phase stepper motors may be considered.
Special-purpose stepper motors can be selected for specific operating environments.
For example, motors designed for resistance to water or oil can be used in applications requiring additional environmental protection.
Special applications should be evaluated according to their specific operating conditions.
Special specifications can be considered when the standard motor does not meet the mechanical requirements.
Potential customization requirements include:
· Shaft diameter
· Shaft length
· Shaft orientation
· Motor dimensions
· Electrical specifications
· Other mechanical requirements
When special specifications are required, it is recommended to communicate with the manufacturer's technical engineers to confirm whether the requested design can be manufactured.
In industrial production, improving equipment efficiency can directly affect manufacturing productivity.
The source material identifies several approaches for improving stepper motor gearbox efficiency:
1. Improve machining accuracy to ISO 5–6 grade.
2. Optimize the gearbox structural design.
3. Improve bearing quality and service life.
4. Improve theoretical calculations and design methods, including gear strength calculations, tooth modification, deformation calculations, optimization design, root fillet transitions, and new structural designs.
· Stepper motor performance depends on proper motor, driver, wiring, and control-system matching.
· Motor heat is mainly associated with copper loss, iron loss, and harmonic losses.
· Six-wire and eight-wire stepper motors have different wiring configurations that affect current, torque, heat, and high-speed performance.
· Holding torque, speed, step angle, current, frame size, and operating environment are important selection factors.
· Higher-speed applications require careful consideration of motor inductance, starting frequency, and acceleration.
· Proper motor-driver matching can help achieve the expected torque and operating performance.
· Special motor specifications can be considered when standard products do not meet mechanical requirements.
Selecting and using a stepper motor effectively requires more than simply choosing a motor with a higher torque rating or larger current.
The motor, driver, wiring configuration, load, speed, positioning requirements, and operating environment all affect the final performance of the motion system.
By evaluating these factors carefully and matching the stepper motor with the appropriate driver, engineers can make better use of the motor's available torque, speed, and positioning capabilities.
For applications requiring special dimensions, shaft configurations, electrical specifications, or environmental protection, customized stepper motor solutions can also be considered.
