How to Use 100:1 Metal Gearmotor 37Dx73L mm 24V with 64 CPR Encoder (Helical Pinion): Examples, Pinouts, and Specs

The 100:1 Metal Gearmotor 37Dx73L mm 24V with 64 CPR Encoder, manufactured by Pololu (Part ID: 4695), is a compact and efficient gearmotor designed for high-torque applications. It features a 100:1 gear ratio, operates at 24V, and includes a built-in quadrature encoder with 64 counts per revolution (CPR) for precise position and speed feedback. The helical pinion design ensures smoother operation and reduced noise compared to traditional straight-cut gears.

• Robotics (e.g., mobile robots, robotic arms)
• Automated systems (e.g., conveyor belts, actuators)
• Precision motion control
• Industrial machinery
• Hobbyist and DIY projects requiring high torque and precise feedback

The motor has two main terminals for power and four additional pins for the encoder. The pinout is as follows:

Note: The encoder outputs are open-drain and require pull-up resistors for proper operation.

1. Powering the Motor:

   • Connect the motor terminals (M+ and M-) to a motor driver capable of handling the motor's voltage (24V) and current (up to 5.5A).
   • Use a motor driver with PWM control for speed regulation.

2. Connecting the Encoder:

   • Supply power to the encoder by connecting the VCC pin to a voltage source (3.5V–20V) and the GND pin to ground.
   • Connect the A and B pins to microcontroller GPIO pins configured as digital inputs.
   • Add pull-up resistors (e.g., 10 kΩ) to the A and B lines if not already provided by the microcontroller.

3. Controlling the Motor:

   • Use a motor driver or H-bridge to control the motor's direction and speed.
   • For precise position or speed control, read the encoder signals (A and B) to determine the motor's rotation and direction.

• Power Supply: Ensure the power supply can provide sufficient current (up to 5.5A) to avoid voltage drops or motor stalling.
• Heat Dissipation: Prolonged operation at high loads may cause the motor to heat up. Allow adequate ventilation or use a heat sink if necessary.
• Encoder Signal Noise: Use shielded cables for the encoder connections to minimize noise interference.
• Mounting: Secure the motor using the mounting holes to prevent vibration or misalignment during operation.

Below is an example of how to read the encoder signals using an Arduino UNO:

// Define encoder pins
const int encoderPinA = 2; // Channel A connected to digital pin 2
const int encoderPinB = 3; // Channel B connected to digital pin 3

volatile int encoderCount = 0; // Variable to store encoder count
int lastEncoded = 0;           // Tracks the last encoder state

void setup() {
  pinMode(encoderPinA, INPUT_PULLUP); // Enable pull-up resistor on pin A
  pinMode(encoderPinB, INPUT_PULLUP); // Enable pull-up resistor on pin B

  // Attach interrupts to encoder pins
  attachInterrupt(digitalPinToInterrupt(encoderPinA), updateEncoder, CHANGE);
  attachInterrupt(digitalPinToInterrupt(encoderPinB), updateEncoder, CHANGE);

  Serial.begin(9600); // Initialize serial communication
}

void loop() {
  // Print the encoder count to the serial monitor
  Serial.print("Encoder Count: ");
  Serial.println(encoderCount);
  delay(100); // Delay for readability
}

void updateEncoder() {
  // Read the current state of the encoder pins
  int MSB = digitalRead(encoderPinA); // Most significant bit
  int LSB = digitalRead(encoderPinB); // Least significant bit

  int encoded = (MSB << 1) | LSB; // Combine the two bits
  int sum = (lastEncoded << 2) | encoded; // Track state changes

  // Update encoder count based on state transitions
  if (sum == 0b1101 || sum == 0b0100 || sum == 0b0010 || sum == 0b1011) encoderCount++;
  if (sum == 0b1110 || sum == 0b0111 || sum == 0b0001 || sum == 0b1000) encoderCount--;

  lastEncoded = encoded; // Update the last state
}

Note: This code assumes the encoder outputs are connected to pins 2 and 3 on the Arduino UNO. Adjust the pin numbers as needed for your setup.

1. Motor Does Not Spin:

   • Cause: Insufficient power supply or incorrect wiring.
   • Solution: Verify the power supply voltage and current. Check the motor driver connections.

2. Encoder Signals Are Unstable:

   • Cause: Electrical noise or missing pull-up resistors.
   • Solution: Use shielded cables for the encoder and add pull-up resistors to the A and B lines.

3. Motor Overheats:

   • Cause: Prolonged operation at high loads or insufficient ventilation.
   • Solution: Reduce the load or provide better cooling.

4. Incorrect Encoder Readings:

   • Cause: Misaligned wiring or incorrect interrupt configuration.
   • Solution: Double-check the encoder pin connections and ensure the microcontroller is configured correctly.

• Q: Can I use this motor with a 12V power supply?

  • A: While the motor is designed for 24V, it can operate at lower voltages with reduced performance (e.g., lower speed and torque).

• Q: What is the maximum RPM of this motor?

  • A: The no-load speed is approximately 100 RPM at 24V.

• Q: Do I need external pull-up resistors for the encoder?

  • A: Yes, the encoder outputs are open-drain and require pull-up resistors for proper operation.

• Q: Can I use this motor for continuous operation?

  • A: Yes, but ensure proper cooling and avoid exceeding the motor's rated load to prevent overheating.