Electronics 114: Stepper Motors & Microstepping Explained
A practical engineering guide to stepper motors: how they really work, why current control matters more than voltage, what microstepping actually does, and how to set up reliable motion systems for 3D printers, CNC machines, and precision positioning projects.
1) What is a stepper motor?
A stepper motor moves in discrete angular steps. Each step is produced by energising motor coils in a specific sequence.
2) Step angle & resolution
The step angle defines how far the shaft rotates per step.
- Common value: 1.8° (200 steps per revolution)
- Some motors: 0.9° (400 steps per revolution)
3) Bipolar vs unipolar steppers
| Type | Wiring | Pros | Cons |
|---|---|---|---|
| Bipolar | 4 wires | Higher torque | Requires H-bridge driver |
| Unipolar | 5–6 wires | Simpler drive | Lower torque |
4) Why current control matters
Stepper coils have low resistance. If driven directly from voltage, current rises too high.
5) What is microstepping?
Microstepping divides a full step into smaller electrical steps by controlling coil current sinusoidally.
- Smoother motion
- Reduced vibration
- Quieter operation
6) Microstepping myths
- Myth: Microstepping increases torque ? false
- Myth: More microsteps = more accuracy ? partially false
7) Stepper driver ICs explained
| Driver | Microsteps | Notes |
|---|---|---|
| A4988 | 1/16 | Cheap, basic |
| DRV8825 | 1/32 | Higher voltage |
| TMC2208 / 2209 | 1/256 (interp.) | Very quiet |
8) Choosing motor voltage & supply
Motor “rated voltage” is misleading. Higher supply voltage allows faster current rise.
9) Torque vs speed behavior
Torque drops as speed increases due to inductance and back EMF.
Fix: Increase supply voltage or reduce acceleration.
10) Thermal limits & cooling
Steppers are designed to run hot.
- 60–80°C case temperature is common
- Drivers need airflow or heatsinks
11) Driver setup checklist
- Set current limit correctly (Vref)
- Confirm coil wiring
- Choose appropriate microstepping
- Add bulk capacitors near driver
12) Common problems & fixes
- Motor vibrates but doesn’t turn ? wrong wiring
- Missed steps ? insufficient torque or acceleration too high
- Overheating driver ? current too high
- Noisy operation ? insufficient microstepping or poor supply
