DIY 3D Printed Robotic Arm Actuator

Today, we will learn how to make a robotic arm actuator from scratch.

The system is based on a planetary gear system and designed using Fusion 360.

The end product is available at the end of this tutorial. Consider downloading the parts on my Printables page!

The entire gear system is 3D printed.

But the following parts will be required for a smoother operation.

All listed parts are from McMaster-Carr but are available in most specialized shops:

• 1x Stepper motor NEMA 17: 6627T64
• 4x Ball bearing 686-2RS: 4668K231
• 1x Ball bearing 7201-2RS: 6680K35
• 4x M2.5 Screw, 22 mm Long: 91292A312
• 4x M2.5 Washer: 91100A110
• 4x M2.5 Hex nut: 90591A270

I've decided to go with a planetary gear system.

I recommend checking this website to help you choose the correct number of planet gears, the number of teeth, and all that according to your desired output ratio.

[Image 1]

Once that's done, you can start designing in Fusion 360. Some plugins like SpurGear (integrated into Fusion360) can help you with the design, but I recommend HelicalGear, as the name suggests, allows you to make Helical gears.

Helical gears allow a quieter operation than straight gears.

In [image 2], we can see some variables from the HelicalGear plugin. To make this tutorial short, I won't go through them. But I recommend checking this video, which contains all the information you need to carry on with your customized planetary gear.

I recommend taking extra care in that video because you will need to modify the ring gear for the planets to adequately fit.

Remember to leave enough backlash since 3D printed parts (FDM in my case) tend to shrink.

In my case, I set -0.35mm for the ring gear and 0.2mm for the others.

With the gear system designed and set up, it's time to make a support for the stepper motor.

In my design, the carrier is an output while the ring gear is static.

Next, you need to take care of the clearances! A real pain, but let me help you overcome this thanks to the tests performed on my Anycubic Predator.

I've printed a test part to verify that the bearings can fit with a push. You can find the results in [image 5].

Overall, for the inner diameter of the bearing -0.15mm is enough, while for the outer diameter, 0.3mm is needed.

NB: Make sure to adapt the tolerances to your printer! For example, FDM tolerances will float with an SLS!

Neither are all FDM printers the same. You can find valuable information at hubs' KB on design guidelines.

Almost there!

If you've made it so far, your parts are ready to be printed! Yet, they need to be organized for an optimal print.

I am using PrusaSlicer, which gives me a lot of freedom. It is a personal choice. I've used Cura in the past, but PrusaSlicer ended as a better fit for my printer.

• Avoid support materials on the gears at all costs. If not properly removed after printing, it will cause interferences.
• Adequately rotate the parts to avoid supports (You can check my rotation setup in [image 6]).
• Make sure to set the seam position to random. Otherwise, some parts might not fit together.
• I've used 0.2mm layer height and 15% infill. The values can be set to one's liking.

The system is operated by an Arduino, with a Stepper driver A4988 powered by a 24V PSU.

Here marks the end of this tutorial.

Congratulation on reaching this far!

If you're still having some issues with parts not fitting, triple-check the clearances or activate External Perimeter First which will make the parts 'ugly-looking' but dimensionally accurate.

Let me know in the comment section what you've printed or if you have any questions!