Eight months ago he built a quadrupedal robot that could step sideways using three of them per leg. I’m not going to link that, you’ll have to find it from his YouTube page because you should look around.
Sorry for going off topic. "Electric Motor Scaling Laws and Inertia in Robot Actuators" by Ben Katz who designed the MIT Mini Cheetah in 2018 is very well known in the legged robotics community. His master’s thesis on actuator design is also widely referenced.
During the COVID period, some Chinese companies even sold variants of actuators inspired by the Mini Cheetah design.
Aaed Musa has also mentioned in some of his videos that his actuator designs were inspired by the Mini Cheetah actuator. Yes, His capstan drive video is especially impressive.
For example, in Aaed Musa’s video "I Built a Rubik's Cube Solving Robot" (https://www.youtube.com/watch?v=m0bMMALYMYk), he states in the description that the design was inspired by Ben Katz’s work.
I did a bit of a deep dive into motor control and actuators in building a two axis gimbal for tracking satellites with an RF antenna (with the eventual goal of building a mount for optical tracking).
Ben's vids were kind of mind-blowing for me at that time. I couldn't believe some of the control that was possible with relatively pedestrian electronics. Aaed's vids do a wonderful job of making it accessible in an applied way.
It's something I think a lot of the folks on HN would find interesting to tinker with. Nice mix of software and hardware that actually does work in physical reality. It also gives me a level of appreciation for the advances in humanoid robots that I don't think I would have had otherwise. (If you *do* get into it, I'd highly recommend getting into field oriented control with brushless motors and encoders. Small hobby servos are fun but they encapsulate a lot of the interesting parts and tend to have limited options available for things like the capstan vid linked above)
Thanks for this. I almost never have the patience for any videos, but this one hooked me and kept me engaged throughout. Worth it for that random "yo mama" joke alone.
This channel about retrofitting industrial robotic arm control systems is quite practical. Could always run the playback at 1.25 speed for slow talkers/edits =3
If you pay attention to Smarter Every Day videos he’s occasionally in the background, which makes me suspect he’s still active but doing behind the scenes stuff and less in his garage.
I hate the phrase "zero backlash" that gets used right in the intro. Nothing has zero backlash. If it did, that would mean the material is incompressible & unstretchable: it would have an infinite speed of sound. You could implement FTL communication using zero-backlash actuators. Capstan drives have backlash because the rope stretches. It's very low if using a low-stretch rope, but nonzero.
Backlash & a lack of stiffness have the same effect, but the cause happens at different scales. Just because the gaps are in between the atoms of the dyneema doesn't mean there are no gaps! There's still play due to a lack of stiffness, just less of it. The positioning errors should be lower than the feedback resolution on the servo encoders, but they won't be zero.
I disagree; backlash is unrelated to force. If you were to graph error over force for backlash it would be a straight line but for something like dyneema it would directly scale with force applied.
In a driven system the dead zone is graphable and that deadzone time or area does not change based on velocity, A lack of rigidity in couplings, gears or belts IS affected by velocity
Dyneema has remarkably low elongation, in addition to its very high strength to weigh ratio. Higher than Kevlar (but less heat resistant). It’s why they used it for sail cloth before rigid body sails took over most competition sailing.
Aaed I believe is preloading his devices, which should eliminate most of the remaining give but also increase wear rate. Though it sounds like from the video that the biggest problem is rubbing the cord against itself, hence the channels to guide the cords.
https://youtube.com/watch?v=MwIBTbumd1Q
Eight months ago he built a quadrupedal robot that could step sideways using three of them per leg. I’m not going to link that, you’ll have to find it from his YouTube page because you should look around.