I’ve been working on a large robot project for a while now, and throughout the process, I kept hearing more and more about 3D-printed cycloidal drives. If you’re not familiar, these are high-torque, precision gear systems that are commonly used in robotics. Naturally, I had to dive in and see what the hype was all about.

I’ve seen a variety of motor-powered cycloidal drives, but I was particularly interested in how a stepper motor would handle one. While large-scale drive arms would be great for my project, I also wanted to explore smaller, light-load-bearing cycloidal drive setups that could work with stepper motors.

Wanting to get straight to testing without reinventing the wheel, I found an excellent open-source 3D Printed Cycloidal Drive for Robot Arms project.

This allowed me to jump right into printing and assembling the drive. However, one key realization struck me—this build only rotates about 190 degrees and doesn’t include stop switches or encoders. That meant I needed a way to control and test its movement, track torque, and evaluate the strain of a NEMA stepper motor.

So, I set out to write some Arduino code to manually control the movement, and was fairly quick to setup.

The Build Process

This project took a few weekends to come together. It didn’t take long to get to trimming and assembling, but at the end I hit my first roadblock—the drive wouldn’t budge. Just as a helpful note, tolerances are really key for this print project. A little bit of silicone grease and some tips from the video helped loosen things up, and before long, I had a functional cycloidal drive ready for testing.

Wiring It Up: The H-Bridge Setup

Now for the fun part—getting the stepper motor moving! Unlike a traditional motor, a stepper requires precise control over each movement. That’s where the H-Bridge motor driver comes in. This little piece of hardware allows us to control the direction and speed of the motor using an Arduino.

Basic Wiring Setup

• Motor power supply → H-Bridge (provides power to the motor)
• H-Bridge outputs → Stepper motor (controls movement direction)
• Arduino control pins → H-Bridge inputs (sends movement commands)

Here’s a simple wiring diagram for reference:

  Arduino          H-Bridge          Stepper Motor
  --------        ----------        --------------
  Pin 8  --------> IN1                
  Pin 9  --------> IN2
  Pin 10 --------> IN3
  Pin 11 --------> IN4
  GND    --------> GND
  5V     --------> VCC
                   Motor 1 + <------- Pin 2
                   Motor 1 - <------- Pin 3   
                   Motor 2 + <------- Pin 4
                   Motor 2 - <------- Pin 5     

With everything wired up, it’s time to write some code to bring it to life!

Writing the Arduino Code

I needed a way to manually position the motor, set a zero reference, define a max position, and create an oscillation mode for repeated movement testing. Here’s what I came up with: https://github.com/macroflux/simple-stepper-motor-robot-arm-test-control

#include <Stepper.h>

const int stepsPerRevolution = 600;
Stepper myStepper(stepsPerRevolution, 8, 9, 10, 11);
int stepSize = 10;
bool oscillate = false;
int maxPosition = 1000;
int currentPosition = 0;

void setup() {
  myStepper.setSpeed(30);
  Serial.begin(9600);
  Serial.println("Stepper Motor Ready. Use + to move forward, - to move back, o to oscillate, s to stop.");
}

void loop() {
  if (Serial.available()) {
    String command = Serial.readStringUntil('\n');
    command.trim();
    if (command == "+") {
      myStepper.step(stepSize);
      currentPosition += stepSize;
      Serial.print("Moved forward. Position: ");
      Serial.println(currentPosition);
    } else if (command == "-") {
      myStepper.step(-stepSize);
      currentPosition -= stepSize;
      Serial.print("Moved backward. Position: ");
      Serial.println(currentPosition);
    } else if (command == "o") {
      oscillate = true;
      Serial.println("Starting oscillation...");
    } else if (command == "s") {
      oscillate = false;
      Serial.println("Stopping motion.");
    }
  }
  if (oscillate) {
    Serial.println("Moving to max position...");
    myStepper.step(maxPosition - currentPosition);
    currentPosition = maxPosition;
    delay(500);
    Serial.println("Returning to zero...");
    myStepper.step(-maxPosition);
    currentPosition = 0;
    delay(500);
  }
}

This script lets me manually move the stepper, define a zero position, set a max range, and run a simple oscillation test to simulate arm movements.

Testing and Results

Once the Arduino code was uploaded, I powered up the setup and put it through its paces. At first, the movements were stiff (probably due to tight tolerances in the 3D-printed parts), but after a few cycles, things started running much smoother. The oscillation mode worked well, cycling the arm back and forth consistently. Joint tested!

Note: I found that this build puts slightly more strain on the stepper than normal pulley and belt application. Depending on power source, the NEMA stepper motor may get very warm.

Final Thoughts

This project was an interesting dive into NEMA stepper motors as alternatives in robotic joints through the cycloidal drive. My takeaways are that this is a great light duty drive and application. Due to oscillation harmonics in the drive, it may not be advisable to push too much speed through the motor, but as the original video poster project used as a goal for lifting moderate weighted equipment, this design is perfect. For next steps I want to continue to involve optimizing movement precision and testing heavier loads to see how well the cycloidal drive holds up.

If you’re into robotics and always wanted to try a straightforward, simple effective cycloidal drive, I highly recommend giving this project a try!