Stepper
A stepper motor moves through a sequence of magnetic alignments as its windings are driven. A 1.8° full-step motor has 200 full steps per revolution. Counting commands estimates position only while the rotor follows them; it does not prove the actual shaft position.
The stator's changing magnetic field pulls a permanent-magnet, variable-reluctance or hybrid rotor toward successive alignments. A suitable driver sequences winding currents. Microstepping uses intermediate current levels for smoother movement, but smaller commanded increments are not a guarantee of equal mechanical accuracy.
In plain terms
A ratchet wheel: instead of turning smoothly, it advances in defined clicks, and the controller can count the clicks to know the position exactly — as long as no step is skipped.
Why designers use it
- Commanding incremental motion with a suitable driver.
- Open-loop positioning where load and acceleration remain within the system's capability.
- Combining a motor with a mechanical transmission to obtain the required travel.
Best for
- 3D printers
- CNC
- Lab instruments
Key specifications
- Motion: Full-step angle, supported drive modes and positioning requirements
- Torque: Distinguish energized holding torque, unpowered detent torque and running torque
- Drive: Winding connection, phase-current limit and compatible driver
- Mechanical load: Check inertia, acceleration, resonance and thermal conditions
When not to use it
- When loss of position cannot be tolerated without feedback or an independent reference.
- When the required torque at speed exceeds the motor-and-driver capability.
- When heating, vibration or resonance cannot be managed.
Common mistakes
- Assuming every commanded step occurred, despite excessive load or acceleration.
- Removing holding current without evaluating the load. Some rotor designs have unpowered detent torque, but it may not hold the mechanism safely.
- Confusing driver supply voltage with the motor winding's current and thermal limits.
- Assuming microstep count equals absolute positioning accuracy.
Where you will find it
- A positioning stage can count drive commands, provided its motor follows them and a reference establishes the starting position.
- For illustration, 200 full steps and 1/16 microstepping give 3,200 commanded increments per revolution. Mechanical accuracy must be evaluated separately.
A short history
Stepper motors convert electrical pulses into discrete mechanical steps by sequentially energizing stator coils, causing a permanent magnet or variable reluctance rotor to align with the resulting magnetic field. This lets users track position by counting steps rather than using a feedback sensor, making steppers useful for precision positioning tasks like driving a 3D printer's table, though they can miss steps under excessive load.
Good to know
- Microstepping increases command resolution; it does not remove load-dependent position error.
- Unpowered detent torque and energized holding torque are different specifications.