Marc Raibert

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243 appearances 1 recordings 1 series first heard Feb 2024 last heard Feb 2024

Marc Raibert’s voice in public audio — every appearance, attributed to the second.

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Lex Fridman Podcast · #412 – Marc Raibert: Boston Dynamics and the Future of Robotics · 16 Feb 2024 podcast

And we made, back in about 1985 or 6, I can't remember, we had a simple robot doing somersaults. To do it in 3D, really the calculation is the same. You just have to be balancing in the other degrees of freedom. If you're just doing a somersault, it's just a planar thing.

When Rob was my graduate student and we were at MIT, which is when we made a two-legged robot do a 3D somersault for the first time. There, in order to get enough rotation rate, you needed to do tucking also. You know, withdraw the legs in order to accelerate it. And he did some really fascinating work on how you stabilize more complicated maneuvers.

You remember he was a gymnast, a champion gymnast before he'd come to me. So he had the physical abilities. And he was an engineer, so he could translate some of that into the math and the algorithms that you need to do that.

Unfortunately, though, humans don't really know how they do it, right? We're coached. We have ways of learning, but do we really understand in a physics way what we're doing? Probably most gymnasts and athletes don't know.

Atlas still doesn't walk like a person, and it still doesn't walk quite as gracefully as a person, even though it's been getting closer and closer. The running might be close to a human, but the walking is still a challenge.

And something weird about the knee, that you can kind of do this folding and unfolding, And get it to work out just, a human can get it to work out just right. There's compliances. Compliance means springiness in the design that are important to how it all works. Well, we used to have a motto at Boston Dynamics in the early days, which was, you have to run before you can walk.

For a quadruped, probably. Of course, it was probably the loudest, too. So we had this little racing go-kart engine on it, and we would get people from three buildings away sending us, complaining about how loud it was.

Well, it's always a balance between wanting to get where you really want to get and what's practical to do based on your resources or what you know and all that. So, I mean, the whole idea of the pogo stick was to do simplification. Obviously, it didn't look like a human.

I think a technical scientist could appreciate that we were capturing some of the things that are important in human locomotion without it looking complicated. like it without having a knee and ankle. I'll tell you the first sketch that Ben Brown made when we were talking about building this thing was a very complicated thing with zillions of springs, lots of joints.

It looked much more like a kangaroo or an ostrich or something like that, things we were paying a lot of attention to at the time. Um, you know, so my job was to, uh, say, okay, well let's do something simpler to get started and maybe we'll get there at some point.

Oh yeah. We, we did, uh, we filmed and digitized, uh, data from horses. I did a dissection of a ostrich at one point, which has absolutely remarkable legs.

Most of it's up in the feathers, but there's a huge amount going on in the feathers, including a knee joint. The knee joints way up there. The thing that's halfway down the leg that looks like a backwards knee is actually the ankle. The thing on the ground, which looks like the foot, is actually the toes. It's an extended toe. Fascinating.

But, you know, the basic morphology is the same in all these animals.

You know, the slow-mos of cheetahs running are incredible. You know, they're they, there's so much back motion and, uh, you know, grace. And of course they're moving very fast. Uh, The animals running away from the cheetah are pretty exciting.

You know, the pronghorn, which, you know, they do this all four legs at once jump called the prong to kind of confuse the, especially if there's a group of them, to confuse whoever's chasing them. So they do like a misdirection type of thing? Yep, they do a misdirection thing.

The front on views of the cheetahs running fast where the tail is whipping around to help in the turns, to help us stabilize in the turns. That's pretty exciting.

But they also turn very fast.

Everything in the body is probably helping turn, because they're chasing something that's trying to get away that's also zigzagging around. But I would be remiss if I didn't say humans are pretty good, too. You watch gymnasts, especially these days, they're doing just incredible stuff.

In Big Dog. Big Dog. Yeah, Big Dog came first, and then Little Dog was later. And you know, there was a... There's a big compromise there. Human knees have multiple muscles, and you could argue that there's, I mean, it's a technical thing about negative work. When you're contracting a joint, but you're pushing out, that's negative work.

And if you don't have a place to store that, it can be very expensive to do negative work. And in Big Dog, there was no place to store negative work in the knees. But Big Dog also had pogo stick springs down below. So part of the action was to comply in a bouncing motion. Later on in Spot, we took that out. As we got further and further away from the leg lab, we had more energy-driven controls.

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