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Open Dynamic Robot Initiative (2020)

open-dynamic-robot-initiative.github.io

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Re: Open Dynamic Robot Initiative (2020)

#21

Post by neotriple »

JabavuAdams wrote: post #20
robomartin wrote: post #18

Earlier quoted context omitted.

> 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 moto…

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?

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).

Re: Open Dynamic Robot Initiative (2020)

#22

Post by neotriple »

mech422 wrote: post #7

How does this relate to MIT's mini-cheetah(1)? A quick search didn't turn up any plans/code for the cheetah except some simulator software(2). Is this an open source 'work-alike' ? 1) https://biomimetics.mit.edu/ 2) https://github.com/mit-biomimetics/Cheetah-Software edit: I don't think the cheetah plans are actually open source ?

The MIT cheetah plans (specifically, having access to things like their motors) are not open source.

Re: Open Dynamic Robot Initiative (2020)

#24

Post by fvncc »

JabavuAdams wrote: post #11
undoware wrote: post #4

Finally, as I get my proteins denatured by a quadruped-mounted face-finding energy weapon in Civil War II, I can go out singing Stallman's song. You will be free, hackers. You will be free

Energy weapons are expensive to build. Chemical weapons are cheap. The War of the Machines is going to be all nerve gas, all the time. :(

Actually chemical weapons don’t do well on “cost effectiveness”, apparently:

https://acoup.blog/2020/03/20/collections-why-dont-we-use-ch...

Re: Open Dynamic Robot Initiative (2020)

#25

Post by Animats »

teraflop wrote: post #17
Animats wrote: post #14

Very nice. What makes this work is the motors.[1] It's using 3-phase drone prop motors with no gear reduction. With direct drive, the mechanics of the joints are simple. Not too expensive, either. Each motor is about US$120. I used to work on legged running back in the 1990s. But there were no motors good enough to build a small machine like this back then. All we had were R/C servos, gearboxes, and screw drive actua…

> It's using 3-phase drone prop motors with no gear reduction. If I'm understanding correctly, this is not accurate. The paper and the Github repository describe it as a "dual stage timing belt transmission with a 3:1 gear reduction on each stage". https://github.com/open-dynamic-robot-initiative/open_robot_...

Aw, you're right. We're still not there on tiny direct drive. I've seen direct drive robots with large "pancake" motors, and thought they were driving those little guys that way. But no. They still need a lot of reduction. I'm surprised that they bounce as well as they do while back-driving through 9:1

Re: Open Dynamic Robot Initiative (2020)

#26

Post by robomartin »

JabavuAdams wrote: post #20
robomartin wrote: post #18

Earlier quoted context omitted.

> 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 moto…

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?

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.

Re: Open Dynamic Robot Initiative (2020)

#27

Post by robomartin »

neotriple wrote: post #21
JabavuAdams wrote: post #20

Earlier quoted context omitted.

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?

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).

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.

Re: Open Dynamic Robot Initiative (2020)

#28

Post by mech422 »

neotriple wrote: post #22
mech422 wrote: post #7

How does this relate to MIT's mini-cheetah(1)? A quick search didn't turn up any plans/code for the cheetah except some simulator software(2). Is this an open source 'work-alike' ? 1) https://biomimetics.mit.edu/ 2) https://github.com/mit-biomimetics/Cheetah-Software edit: I don't think the cheetah plans are actually open source ?

The MIT cheetah plans (specifically, having access to things like their motors) are not open source.

Bummer. Thanks for clarifying that.

Re: Open Dynamic Robot Initiative (2020)

#29

Post by Animats »

robomartin wrote: post #18
Animats wrote: post #14

Very nice. What makes this work is the motors.[1] It's using 3-phase drone prop motors with no gear reduction. With direct drive, the mechanics of the joints are simple. Not too expensive, either. Each motor is about US$120. I used to work on legged running back in the 1990s. But there were no motors good enough to build a small machine like this back then. All we had were R/C servos, gearboxes, and screw drive actua…

> 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 moto…

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.

Re: Open Dynamic Robot Initiative (2020)

#30

Post by Animats »

robotresearcher wrote: post #13
heavyset_go wrote: post #8

I have an tangential question about open source projects and names. "Boston Dynamics" is a trademark of Boston Dynamics Inc. Can using "Dynamic" like this project does cause legal problems, considering the name can be an allusion to the trademark?

I doubt it. Canadian chain restaurant 'Boston Pizza' can't prevent you using the word 'pizza', though it's directly concerned with their business. General Dynamics predates Boston Dynamics by decades. ('General Dynamics' is a wonderful company name. Imagine if you'd heard it for the first time today. Cool name.)

It's very 1950s.

* General Dynamics

* General Atomic

* General Houses (briefly, late 1940s)

following, of course

* General Motors

* General Electric

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