Building a Cycloidal Robotic Actuator

YouTuber Koshiro Robot Creator (KRC) has decided to build a quadruped robot to sharpen his technical skills. Constructing such a robot, however, requires a significant amount of background knowledge and technology, including powerful yet compact actuators to control joint movement. Rather than simply buying such actuators – which would mean skipping out on a potential learning opportunity – KRC instead decided to spec’, design, and manufacture one himself, as outlined in the video below.

In the first part of the video, KRC first explains why an outrunner BLDC (brushless DC) motor – featuring moderate speed and high torque – would work best. Another advantage is that there is a significant amount of space in the middle of the motor that can be used for gear reduction. This can take the form of a planetary, cycloidal, or harmonic gear arrangement. He decided on a cycloidal setup, highlighting this gear system’s robustness and high-torque capabilities.

To meet this type of gearing’s relatively complicated machining requirements, the design was manufactured by JLC3DP, which sponsored the video. With parts in hand, KRC then assembled everything together with bearings and grease, and wrapped the stator, first with 20, then 22 AWG wire.

As shown at the end of the video, the device is demonstrated with a benchtop power supply and a low-cost ESC. While it takes a little push to get started, and it makes some contact (and noise) while spinning, with a bit more work this design can hopefully become a critical element in KRC’s future four-legged walker. The CAD model is found here on GitHub if you would like to examine it in more detail.