The 5439 Workshop Takes a Novel Approach to a 3D-Printable Bipedal Robot Actuator
A twist on the rope-drive approach could deliver a more compact yet still robust 3D printed actuator, if teething issues can be resolved.
Pseudonymous YouTuber "The 5439 Workshop," hereafter simply "5439," is working on a project to build a bipedal robot — beginning with designing a novel type of 3D-printable actuator, driven by an Espressif ESP32 microcontroller.
"I've wanted to build a bipedal robot for a long time — and now it's finally happening! I'm taking the Disney walking robot as inspiration, but I will make it my own design," 5439 explains. "The thing I love about it is that it is full of character and animated not only for efficiency but to also to convey emotions in the way it moves. I'm designing custom 3D-printed robotic actuators — the core of the robot. Instead of using the typical setup when it comes to a rope/cable drivetrain, I've developed a new actuator design (at least I haven't seen this exact approach before!). It's not the easiest way, but it's the path I enjoy."
The problem 5439 is trying to solve — other than an itch to do something new — is simple: the tendency for 3D-printed actuators to wear out too soon. The typical fix for this is to use a rope-drive system instead of traditional gears, which is better suited to 3D printing but results in a bulkier actuator than desired.
"Here's the idea," 5439 says of the project's novel approach. "We'll take the rope drive and bend it over two pulleys. Then we'll take the driver and open it up so it fits around the drive train. And finally, we place the encoder inside of the stator."
Initial testing of the design showed an issue with flexing, which limited the torque to around 6.5 newton-meters (Nm). The addition of metal sheets increased rigidity, but the torque still didn't scale: 1A delivered 5Nm, but 5A only raised that to 9Nm. "I tried a bunch of stuff," 5439 says, "until I found this: the pulley wheels are splitting at higher forces, creating a lot of friction and resistance. This explains our results."
The full video is available embedded above and on 5439's YouTube channel; design files for the actuator have not yet been publicly released.