Stepper motors

Learn

What you’ll learn

• How a stepper moves in exact steps
• The two common types and their drivers
• When to choose a stepper instead of a servo or DC motor

Steps

A stepper has several coils. Energising them in sequence pulls the rotor round one step at a time. A common NEMA 17 motor has 200 steps per revolution (1.8° per step). Count steps and you know the position exactly, with no sensor, as long as it never skips steps.

Two common types

Motor	Driver	Notes
28BYJ-48 (5 V, unipolar, geared)	ULN2003 board	Cheap, slow, about 2048 steps per output turn
NEMA 17 (bipolar)	A4988, DRV8825, TMC2208	Used in 3D printers; strong and precise

Drivers like the A4988 need only two pins: STEP (one pulse = one step) and DIR (direction). They also offer microstepping (1/2, 1/4 … 1/16 steps) for smoother, quieter motion.

Choosing a motor

Need	Use
Spin continuously, fast (wheels)	DC gear motor
Go to an angle within ~180°	Servo
Many exact positions, full turns, holding torque	Stepper

Caution

Steppers draw current even when standing still and can get hot. Set the current limit on driver boards like the A4988 before use.

Examples

Example: A4988 STEP/DIR control

const int STEP = 3, DIR = 4;

void setup() {
  pinMode(STEP, OUTPUT);
  pinMode(DIR, OUTPUT);
}

void loop() {
  digitalWrite(DIR, HIGH);
  for (int i = 0; i < 200; i++) {   // one turn
    digitalWrite(STEP, HIGH); delayMicroseconds(800);
    digitalWrite(STEP, LOW);  delayMicroseconds(800);
  }
  delay(1000);
}

Example: how far is one step?

A lead screw moves 8 mm per turn. With 200 steps per turn: 8 ÷ 200 = 0.04 mm per step. With 1/16 microstepping: 0.0025 mm. That’s why 3D printers are so precise.

Practice

Try it in the virtual Arduino

Press Start simulator, replace diagram.json, paste the sketch and press ▶. (In the simulator the stepper connects straight to the pins; a real one always needs a driver board.) If Wokwi says a library is missing, click its Install button and press ▶ again.

diagram.json

{
  "version": 1,
  "author": "RoboLearn",
  "editor": "wokwi",
  "parts": [
    {
      "type": "wokwi-arduino-uno",
      "id": "uno",
      "top": 0,
      "left": 0,
      "attrs": {}
    },
    {
      "type": "wokwi-stepper-motor",
      "id": "stepper1",
      "top": -170,
      "left": 140,
      "attrs": {
        "size": "17"
      }
    }
  ],
  "connections": [
    [
      "stepper1:A-",
      "uno:8",
      "green",
      []
    ],
    [
      "stepper1:A+",
      "uno:9",
      "green",
      []
    ],
    [
      "stepper1:B+",
      "uno:10",
      "blue",
      []
    ],
    [
      "stepper1:B-",
      "uno:11",
      "blue",
      []
    ]
  ],
  "dependencies": {}
}

sketch.ino

#include <Stepper.h>

const int STEPS_PER_REV = 200;   // 1.8° per step
Stepper motor(STEPS_PER_REV, 8, 9, 10, 11);

void setup() {
  motor.setSpeed(30);            // rpm
}

void loop() {
  motor.step(STEPS_PER_REV);     // one full turn
  delay(500);
  motor.step(-STEPS_PER_REV / 2);  // half a turn the other way
  delay(500);
}

Stepper motorOpen full screen ↗

Start simulator

Runs on Wokwi, free, no account needed.

Quarter turnsEasy

Make the stepper move a quarter turn, pause, and repeat. motor.step(50); (200 ÷ 4) followed by delay(500);

Exact angleMedium

How many steps for 135° with a 1.8° stepper? 135 ÷ 1.8 = 75 steps.

Clock handHard

Make the stepper act like a seconds hand: one full turn per 60 seconds, in 60 even ticks. 200 steps ÷ 60 ticks isn’t a whole number. Keep a running total so the error doesn’t add up.

Show an answer

int done = 0;
void loop() {
  for (int tick = 1; tick <= 60; tick++) {
    int target = tick * 200 / 60;   // where we should be
    motor.step(target - done);
    done = target;
    delay(1000);
  }
  done = 0;
}

Quick check

1. How many steps per turn does a 1.8° stepper have?

100180200360

2. What do the A4988’s STEP and DIR pins do?

Measure speedOne pulse = one step; DIR sets directionSet the voltageRead the angle

3. Best motor for a printer that needs many exact positions?

DC motorStepperBuzzerSolenoid

Check my answers