A stepper motor is an electric motor that turns in small, repeatable angle increments instead of spinning freely like a simple DC motor. This makes it useful in robotics, 3D printers, CNC machines, camera sliders, and lab instruments where position control matters. A hybrid stepper motor combines a toothed permanent magnet rotor with toothed stator poles to create precise magnetic alignment positions.
Each electrical pulse sent to the motor driver moves the shaft by one step or a fraction of a step.
Key Facts
- Step angle = 360 degrees / steps per revolution
- Position change = number of steps x step angle
- Hybrid steppers commonly have 200 full steps per revolution, so step angle = 1.8 degrees
- Torque tends to decrease as speed increases because coil current has less time to rise
- Holding torque is the maximum torque a powered stepper can resist while stopped
- Microstep angle = full step angle / microsteps per full step
Vocabulary
- Stepper motor
- A motor that moves its shaft in discrete angular steps controlled by electrical pulses.
- Hybrid stepper motor
- A stepper motor that uses a permanent magnet toothed rotor and toothed stator poles for high positioning accuracy.
- Phase coil
- A winding in the stator that creates a magnetic field when current flows through it.
- Microstepping
- A driving method that uses controlled current levels in multiple phases to divide a full step into smaller motion increments.
- Holding torque
- The torque a powered stepper motor can resist without moving from its commanded position.
Common Mistakes to Avoid
- Assuming a stepper always reaches every commanded step, because open-loop control does not measure the actual shaft position and missed steps can occur under overload.
- Ignoring the torque-speed curve, because a motor that has high holding torque may produce much less usable torque at high speed.
- Connecting a stepper directly to a microcontroller pin, because the coils require a motor driver that can switch higher current and control phase current safely.
- Confusing microstepping with perfect accuracy, because smaller commanded increments make motion smoother but mechanical friction, load, and motor geometry still limit true position accuracy.
Practice Questions
- 1 A hybrid stepper motor has 200 full steps per revolution. What is its full step angle in degrees?
- 2 A 1.8 degree stepper is driven at 16 microsteps per full step. How many microsteps are needed for one full revolution?
- 3 A robot arm joint uses a stepper motor without an encoder. Explain why the controller may think the joint is in the correct position even after the motor has missed steps.