[robomartin]

> no gear reduction

It's 3:1 belt drive reduction.

I was involved in building --or more accurately, rebuilding-- one. I went as far as doing a whole new design CNC-machined out of aluminum.

One of the problems with this design is that these drone motors are not designed for static operation drawing lots of current without any cooling whatsoever. The 3D printed plastic parts are pretty much insulators. We had one motor smoking. The thing could not stand due to its own weight. This (and other factors) led to thinking of a new design using similar principles, a better motor and an aluminum structure that could be used to move some of the heat away from the motors.

[Animats]

cooling

I was wondering about that. The big innovation from Schaft was that they liquid-cooled their motors. That allowed them to build a full size humanoid without going hydraulic.

What happened that made electric motors so much better since the 90’s? It’s not like we made groundbreaking discoveries about magnetism, right?

Neodymium-cobalt magnets and 3-phase drive in small packages. Also, a big market for high-power low-weight drone motors brought the price down.

http://moticont.com/direct-drive-linear-motors.htm

That's a nice little device. Those might make good finger actuators.

Linear motors have long been a tiny niche. I'd looked at Aura linear motors, which was the leading brand back in the 1990s, but Aura got themselves into serious legal trouble. They're back now, but mostly as an aerospace supplier. Power to weight ratio in small linear motors has seldom been good. It's not clear whether this is fundamental or just lack of engineering effort due to small demand.

[JabavuAdams]

Thanks, that's great info. Am I mistaken in remembering that the video shows the thing standing? Is it actually not capable of this? Or is there some very short time-limit?

[robomartin]

I am sure it is. However, the design uses very expensive custom boards to save a lot of weight. The build I was involved with used Odrives and that was enough to have issues. Pre-stretching the belts is also important.

If I had to guess I would suggest that, while 3D printing is a great enabling technology one of the issues it suffers from is that of tolerances. I'll preface this by saying I did not take any measurements at all on the parts as printed. If I did, I would not be surprised to discover issues that, in the aggregate, could lead to performance issues.

[neotriple]

The robot definitely stands. In fact, it can do pretty dynamic things:

https://www.youtube.com/watch?v=YJnbFJ-8Fkg

That said, the platform does have its faults and requires a lot of hardware maintenance, but it certainly can stand and move around (walk around).

[robomartin]

The one I was involved with could never jump like that. My guess is that umbilical, at a minimum, carries power. Based on what I know, I cannot imagine the robot doing what is shown on these videos while loaded with the two battery packs that are part of the design.

Please keep in mind that this is a single data point. I am sure there have been many successful builds. It's a nice design. I was not intimately involved in the original build of the robot we dealt with. I was involved in a complete tear-down and reconfiguration to make it work. As I mentioned, this led to the design of a lightweight quadruped that is fully CNC machined and uses more powerful and capable customized drone motors.

[neotriple]

I'd be curious to learn more about the motor selection for the complete tear down and rebuild. One of the biggest buys of the Solo (in the article) design is the 'high bandwidth' current/torque control, and the price/performance seemed (at the time) to be pretty great.