Stepper Motor, NEMA17, 1.7A, 1.8°, 42x42x40mm, Bipolar

The NEMA17 JK42HS40-1704 stepper motor is a bipolar hybrid motor with 4 wires, used for axis movement in 3D printers, CNC routers, laser engravers and other linear positioning systems where precise, step-based rotation is needed, without a position sensor.

To work, it absolutely needs a driver with current control, for example A4988, and a microcontroller that generates the step pulses. In this tutorial we use an Arduino Uno R3 board and an A4988 driver, the most commonly used combination for this type of motor in 3D printing and CNC projects.

How it works:

The motor has a step angle of 1.8 degrees, meaning 360 divided by 1.8 results in 200 steps for a full rotation, when driven in full step mode. Each pulse applied to the STEP pin of the driver makes the coils switch to another polarity combination, the rotor advancing by a single step.

The rotation speed is given by the frequency of the STEP pulses. The formula is frequency in Hz equals speed in RPM multiplied by the number of steps per rotation, all divided by 60. For example, for 60 RPM in full step mode, this results in 60 x 200 divided by 60, that is 200 Hz, so a STEP pulse every 5 ms.

The A4988 driver also allows microstepping, meaning it divides each full step into substeps, for example at 1/16 microstep this results in 200 x 16, that is 3200 steps per rotation, for a finer and quieter movement.

The current through the coils is limited from the potentiometer on the driver, following the formula Vref equals the desired current multiplied by 8 and by the sense resistor Rs. For an Rs of 0.1 ohm, marked R100 on most A4988 boards, the formula becomes Vref equals the current multiplied by 0.8. For this motor, with a rated current of 1.7 A, a limit of 1.2 to 1.5 A is recommended for long-term operation, that is a Vref between 0.96 and 1.2 V.

What you need:

• 1 x NEMA17 Stepper Motor 1.7A 1.8 degrees 42x42x40mm Bipolar
• 1 x Uno R3 Development Board with ESP8266 Wifi, Arduino compatible
• 1 x A4988 Stepper Driver + Heatsink
• 1 x 12V, 2A Power Supply
• 1 x 100uF Electrolytic Capacitor
• 1 x 40 Dupont Wires 10cm, Female-Female
• 1 x Breadboard 830 points MB-102

Wiring:

The motor is connected to the coil outputs of the A4988 driver, and the driver is connected to Arduino for the control signals and separately to an external 12 - 24 VDC power source for powering the motor.

The driver is powered separately on VMOT and GND with 12 - 24 VDC from an external source, not from Arduino, while VDD and logic GND are connected to 5V and GND on the Arduino. STEP is connected to D3, DIR to D2, and ENABLE to D4. The motor power wires work at a voltage higher than 5V, so they should never be connected directly to the Arduino pins. Install an electrolytic capacitor of at least 100 uF between VMOT and GND, as close as possible to the driver.

Board and libraries:

In Arduino IDE select the Arduino Uno board from the Arduino AVR Boards package, which comes included by default with Arduino IDE and does not require an additional URL in Preferences. The program only uses the standard digitalWrite and delayMicroseconds functions, so you do not need to install any library.

The code:

The code rotates the motor one full rotation clockwise, then one full rotation counterclockwise, repeating the cycle and displaying each stage on the serial monitor.

/*
  Board: Arduino Uno (Arduino AVR Boards)
  Driver: A4988 Stepper Motor Driver
  Motor: NEMA17 stepper motor JK42HS40-1704, bipolar, 1.8 deg/step (200 steps/rev)
  Wiring:
    A4988 STEP   -> Arduino D3
    A4988 DIR    -> Arduino D2
    A4988 ENABLE -> Arduino D4
    A4988 VDD    -> Arduino 5V
    A4988 GND (logic) -> Arduino GND
    A4988 1A / 1B -> Motor coil A (black / green)
    A4988 2A / 2B -> Motor coil B (red / blue)
    A4988 VMOT   -> External 12-24V power supply (+)
    A4988 GND (power) -> External power supply GND
  Libraries: none required, uses only the built in digitalWrite and delayMicroseconds functions
*/
const int stepPin = 3;
const int dirPin = 2;
const int enablePin = 4;
const int stepsPerRevolution = 200;
int stepDelayMicros = 1000;
void rotateSteps(int steps, bool clockwise) {
  digitalWrite(dirPin, clockwise ? HIGH : LOW);
  for (int i = 0; i < steps; i++) {
    digitalWrite(stepPin, HIGH);
    delayMicroseconds(stepDelayMicros);
    digitalWrite(stepPin, LOW);
    delayMicroseconds(stepDelayMicros);
  }
}
void setup() {
  Serial.begin(9600);
  pinMode(stepPin, OUTPUT);
  pinMode(dirPin, OUTPUT);
  pinMode(enablePin, OUTPUT);
  digitalWrite(enablePin, LOW);
  Serial.println("NEMA17 stepper motor ready");
}
void loop() {
  Serial.println("Rotating one full turn clockwise");
  rotateSteps(stepsPerRevolution, true);
  delay(1000);
  Serial.println("Rotating one full turn counterclockwise");
  rotateSteps(stepsPerRevolution, false);
  delay(1000);
}

How the code works:

At the beginning of the program the stepPin, dirPin and enablePin pins are defined, along with the number of steps per rotation stepsPerRevolution and the stepDelayMicros variable which controls the speed, a smaller delay meaning a higher speed.

In the setup function the pins are configured as outputs and the driver is enabled with digitalWrite on enablePin set to LOW, since A4988 has inverted enable logic, and serial communication starts at 9600 baud.

The rotateSteps function takes the number of steps and the direction, sets the dirPin pin according to the desired direction, then sends pulses on stepPin, each pulse consisting of a HIGH edge followed by a LOW edge, separated by the stepDelayMicros interval.

In the loop function, rotateSteps is called for a full rotation clockwise, then waits one second, then is called again for a full rotation counterclockwise, the cycle repeating indefinitely.

Result:

Open the serial monitor at 9600 baud. You will see the status messages, and the motor will visibly perform one full rotation in each direction, with a one second pause between them.

NEMA17 stepper motor ready
Rotating one full turn clockwise
Rotating one full turn counterclockwise
Rotating one full turn clockwise
Rotating one full turn counterclockwise
Rotating one full turn clockwise
Rotating one full turn counterclockwise

Common issues:

The motor vibrates but does not rotate: one of the coil pairs is wrong. Check with a multimeter that the black and green wires form one coil, and red and blue the other coil, and that each pair is connected to the same driver output (1A/1B, respectively 2A/2B).

The motor does not move at all: check that the driver is powered on VMOT with 12 - 24 VDC, that the ENABLE pin is LOW and that the GND wire of the external power source is common with the Arduino GND.

The motor loses steps or skips movements at high speed: the Vref current limit is too low for the load, or the requested speed is too high for the available torque. Slightly increase Vref, within the limit of 1.5 A, or reduce the speed by decreasing the stepDelayMicros value.

The driver or motor gets very hot: the current is set too close to 1.7 A without sufficient cooling. Install a heatsink on the A4988 and reduce Vref towards 1.2 A for long-term operation.

The motor rotates in the opposite direction from what you expect: swap the wires of a single coil, for example black with green, or change the value sent to dirPin in the code.

Limitations and tips:

The control is in open loop, without position feedback, so under too high a mechanical load the motor may lose steps without the driver or program knowing it. The available torque decreases as the rotation speed increases, so for fast applications a compromise is needed between speed and required torque. For quieter and finer movement you can replace the A4988 with a driver with finer microstepping, for example TMC2208 or TMC2209. Make sure the external power supply can provide the current needed for all motors connected simultaneously in a multi-axis system.