[robomartin]

> these are all AI issues (as opposed to mechanical ones)

Actuation is still a massive problem in humanoid robotics. We have over 650 muscles. A humanoid today can't even approximate that. Sure, a robot might not need that many actuators to be extremely useful. However, to be general enough to be able to interact with any human environment, the number of required actuators will not be trivial.

Add to that gearing, couplings, driver electronics, encoders, thermal management, calibration, noise, maintenance and other per-actuator requirements and the picture quickly becomes overwhelming.

This is an area that is still looking for a significant breakthrough.

[Animats]

The big breakthroughs have already happened.

- Small, powerful 3-phase servomotors are cheap and easy to obtain. Mass production of drone motors has advanced small motor technology considerably. Tiny motors use to be either toy-grade junk or expensive Swiss precision. That's improved.

- Motors with built-in encoders are, at last, available. Encoders used to be fragile plastic boxes stuck on the end of the motor. Also, thermal sensing inside the motor is common, so you can tell if you're overheating it.

- Permanent magnets are small and powerful, and have such high coercitivity that you don't have to worry about demagnetizing them if you over-drive the motor. The main limit on motor power is cooling. You can way overdrive a motor momentarily, like muscles.

- Motor controllers are now small and cheap, They cost about $1000 per motor two decades ago. The power semiconductors are small. Controllers can be programmed to use very high power levels briefly, monitoring thermal sensors.

It would be nice to have good linear actuators. Linear motors do exist, but never really became a big thing.

[ebalit]

I'm totally with you on the evolution of motor tech because of drone and also personal mobility (scooters and hoverboard motors are a steal for what they can handle).

While high torque motors got way cheaper, especially with MIT Cheetah "clones" getting easily available, they're still at least 200-500 a pop (depending on the torque needed for each articulation) from what I could find.

I might not know where to search for the real gems though. Where do you search for cheap powerful servomotors?

[tim333]

It's impressive how well the hardware seems to work now, though the software is still clunky. You can see how well the hardware works under human nervous control in the recent MIT bionic foot https://youtu.be/1tD7qd68i3o?t=36

(from https://spectrum.ieee.org/prosthetic-leg)

[imtringued]

We need better electroactive polymers.