Introduction: How to 3D Print a Multi-Stage Planetary Gearbox
A few months ago I got interested in planetary gearboxes. I want to eventually make a robotic arm using this type of actuator, that could lift something heavier than a phone while still being cost effective. So I started looking look around the internet on how to design one of this types of gearboxes, and in this instructable I will be sharing with you what I found.
- Access to a 3D printer
- A motor - It could be any kind of motor ( brushed DC, Stepper, brush-less, etc.)
- Variable power supply
- An Arduino board
- An L298N motor driver
- A joystick
Step 1: Gear Specifications
To be able to design each of the gears, I first needed to layout the known's and make some assumptions.
- Motor RPM = 2100 rev/min
- Train value "e" = 2/8 = 0.25
- Sun gear teeth = 16
- Planet gears teeth = 24
- Ring gear teeth = 64
- Material = PLA
- Train value "e" = 0.25
- pressure angle = 20 degrees
- module (sun and planet gears) = 0.75 mm
- module (ring gear) = 0.76 mm
- backlash (sun and planet gears) = 0.6 mm
- backlash (ring gear) = -0.5 mm
- Gear thickness = 4 mm
With the information above I calculated the center distance of the gears, the pitch diameters and approximated the output rpm of each stage. I wrote the equations in a colab notebook if you guys want to try different tooth numbers. Then I used a CAD software (Fusion 360) to create each of the gears.
Step 2: Design the Housing
When designing the housing I tried to make it as compact as possible. In addition to that I wanted the gearbox to be modular. I want use this gearbox for several different projects like a robot arm, an rc car or a two wheel balancing bot in the future. So by having the flexibility of adding or subtracting stages to the gearbox, I can vary the output rpm and torque, to make it suitable for each project. You can find "STL" files for this design on my thingiverse.
Step 3: Print the Parts
I used Cura Ultimaker to slice the parts. For the gears I printed them with rafts, all the other parts I just used a skirt. I know I don't have the best settings at the moment, but they work for now. If you guys have suggestions on how to improve this settings let me know below.
Step 4: Test the Final Product and Future Iterations
To test the gearbox I attached a rod I had laying around, to see how much it could lift.
I used a variable power supply, an Arduino board, a joystick, and an L298N motor driver to perform the tests. The code that I used can be found in my github, it is modified from other creators like How To Mechatronics, Braini Bits, and DroneBot Workshop. I recommend checking them out if you are looking for a more thorough explanation on how to program the motor driver.
I tested lifting a motor with a slightly bigger gearbox at 9 and 12 volts, but it did not perform very well. I kept increasing the voltage and saw the best results at 18 volts or higher.
In future iterations I hope to reduce the backlash and to design a better housing, so that it can stand on its own when testing. I would also like to compare spur gears vs helical gears to see if there is any difference in performance between them.
Participated in the
Make it Move Contest 2020