Stepper Motor
Motor
A motor that moves in precise, discrete steps when energized in sequence, ideal for position control without sensors.
Schematic symbol
Motor
How stepper motor appears in a circuit diagram.
Types & variants
Key specs
Step angle
degrees (°)Degrees per step (common: 1.8° = 200 steps/rev). Smaller = more precision.
Holding torque
N·m or kg·cmTorque when energized but not moving. Must exceed load torque.
Voltage rating
VNominal voltage per coil. Higher voltage = faster response (with driver).
Current rating
AMax current per coil. Driver must supply this.
Steps per revolution
steps/revTotal steps for full rotation (e.g., 200, 400, 1000).
Laws that govern it
- Lorentz force lawF = q(E + v × B)
Each energised phase pulls the rotor to a defined magnetic position — the discrete steps you count instead of measuring.
- Self-inductance formula — v = L di/dtv = L × di/dt, E = ½LI²
v = L·di/dt is the stepper's speed limit: at high step rates the current has no time to reach full value, so torque falls off a cliff.
- Hopkinson's law — reluctance formulaMMF = Φ × S, S = l / (μ₀μᵣA)
Detent torque with the power off is reluctance: the rotor prefers the lowest-reluctance alignment even without current.
- Lenz's lawthe minus sign in EMF = −N × dΦ/dt
Back-EMF from a hand-spun stepper is genuinely large — it is a generator, which is why drivers get destroyed by disconnecting a spinning motor.
Each law is stated in full — with its diagram, variables and worked meaning — on the electrical laws page.
How it compares
- Stepper Motor vs Servo Motor
Side by side with Servo Motor — specs, variants and which one the job calls for.
Markings
Usually labeled with voltage, current, step angle, and model number. Bipolar motors have 2 coils; unipolar have 4 or 5 wires (center tap).
Standard values
Common step angles: 1.8° (200 steps/rev), 0.9° (400 steps/rev), 7.5° (48 steps/rev). Voltage: 5V, 12V, 24V, 48V. Current: 0.5A to 5A.
How to choose
1) Determine required torque and speed. 2) Choose step angle for precision needs. 3) Match voltage/current to driver. 4) Consider size/weight constraints. 5) Bipolar for more torque, unipolar for simpler wiring.
Pinout & package
4-wire (bipolar: 2 coils), 5-wire (unipolar: 2 coils + center tap), 6-wire (unipolar: 2 coils + dual center tap). NEMA sizes (e.g., NEMA 17) define mounting pattern.
Example circuits
- 3D printer axis control
- CNC machine positioning
- Camera lens focus system
- Robot joint movement
- Linear actuators
Common failures
Coil burnout (overheating from excessive current), gear wear (reduced torque/noise), shaft binding (mechanical overload), missed steps (load exceeds torque).
How to test
1) Check coil continuity with multimeter (should show low resistance between coil pairs). 2) Test for shorts between coils or to motor case (infinite resistance). 3) Test shaft for free rotation.
Substitutes
Brushless DC motors with encoder for smoother motion; servo motors for closed-loop control; different size/step angle if torque/speed requirements allow.