Russ Tedrake is a roboticist and professor at MIT and vice president of robotics research at TRI. He works on control of robots in interesting, complicated, underactuated, stochastic, difficult to model situations.

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EPISODE LINKS:
Russ's Website: http://groups.csail.mit.edu/locomotion/russt.html
Russ's YouTube: https://www.youtube.com/watch?v=_1CtAHVea8I
TRI: https://www.tri.global/team/dr-russ-tedrake
Underactuated Robotics: http://underactuated.mit.edu
Drake: https://drake.mit.edu

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OUTLINE:
0:00 - Introduction
4:29 - Passive dynamic walking
9:40 - Animal movement
13:34 - Control vs Dynamics
15:49 - Bipedal walking
20:56 - Running barefoot
33:01 - Think rigorously with machine learning
44:05 - DARPA Robotics Challenge
1:07:14 - When will a robot become UFC champion
1:18:32 - Black Mirror Robot Dog
1:34:01 - Robot control
1:47:00 - Simulating robots
2:00:33 - Home robotics
2:03:40 - Soft robotics
2:07:25 - Underactuated robotics
2:20:42 - Touch
2:28:55 - Book recommendations
2:40:08 - Advice to young people
2:44:20 - Meaning of life

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The following is a conversation with Russ Tedrick, a roboticist and professor at MIT and vice president of robotics research at Toyota Research Institute or TRI.

He works on control of robots in interesting, complicated, underactuated, stochastic, difficult to model situations.

We'll get into a lot of topics in this conversation from his time leading MIT's DARPA Robotics Challenge Team to the awesome fact that he often runs close to a marathon a day, to and from work, barefoot.

For a world-class roboticist interested in elegant, efficient control of underactuated dynamical systems, like the human body, This fact makes Russ 1 of the most fascinating people I know.

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And now here's my conversation with Russ Tedrick.

What is the most beautiful motion of a animal or robot that you've ever seen?

I think the most beautiful motion of a animal or robot that you've ever seen?

I think the most beautiful motion of a robot has to be the passive dynamic walkers.

I think there's just something fundamentally beautiful.

The ones in particular that Steve Collins built with Andy Ruina at Cornell, a 3D walking machine, so it was not confined to a boom or a plane, that you put it on top of a small ramp, give it a little push, it's powered only by gravity.

No controllers, no batteries whatsoever, It just falls down the ramp.

And at the time, it looked more natural, more graceful, more human-like than any robot we'd seen to date.

Well, okay, the simplest model, it's kind of like a slinky.

1 of the simplest models we use to think about it is actually a rimless wheel.

So imagine taking a bicycle wheel, but take the rim off.

If you give that a push, it still wants to roll down the ramp, but every time its foot, its spoke comes around and hits the ground, it loses a little energy.

Every time it takes a step forward, it gains a little energy.

Those things can come into perfect balance and actually they want to.

If it's going too fast, it'll slow down and it comes into a stable periodic motion.

Now you can take that rimless wheel, which doesn't look very much like a human walking, take all the extra spokes away, put a hinge in the middle.

That can still, you give it a little push, starts falling down a ramp.

Looks a little bit more like walking, at least it's a biped.

But what Steve and Andy and, Tad McGeer started the whole exercise, but what Steve and Andy did was they took it to this beautiful conclusion where they built something that had knees, arms, a torso, the arms swung naturally, give it a little push, and that looked like a stroll through the park.

I think there's a science to getting close to the solution.

I think there's certainly art in the way that they made a beautiful robot.

But then the finesse, because they were working with a system that wasn't perfectly modeled, wasn't perfectly controlled, There's all these little tricks that you have to tune the suction cups at the knees, for instance, so that they stick, but then they release at just the right time.

Or there's all these little tricks of the trade, which really are art, but it was a point.

We were at that time, the walking robot, the best walking robot in the world was Honda's ASIMO.

This was in 97 when they first released it sort of announced P2 and then it went through, it was ASIMO by then in

And it looks like this very cautious walking, like you're walking on hot coals or something like that.

Neither was Atlas when we worked on Atlas.

None of our robots that have been that complicated have been very energy efficient.

But there's a thing that happens when you do control, when you try to control a system of that complexity.

You try to use your motors to basically Counteract gravity.

Take whatever the world's doing to you and push back.

Erase the dynamics of the world and impose the dynamics you want because you can make them simple and analyzable, mathematically simple.

And this was a very sort of beautiful example that you don't have to do that.

And you just have to give it a little bit of energy.

To walk on the flat, you have to give a little energy at some point.

But maybe instead of trying to take the forces imparted to you by the world and replacing them, what we should be doing is letting the world push us around and we go with the flow.

Yeah, but okay, so that sounds very zen, but I can also imagine how many like failed versions they had to go through.

Like how many, like I would say it's probably, would you say it's in the thousands that they've had to have the system fall down before they figured out how to get it?

I don't know if it's thousands, but it's a lot.

It takes some patience, there's no question.

So in that sense, control might help a little bit.

Oh, I think Everybody, even at the time, said that the answer is to do that with control.

But it was just pointing out that maybe the way we're doing control right now isn't the way we should.

The ones that figured out how to move efficiently?

Is there anything you find inspiring or beautiful in the movement of any particular animal?

So it sort of goes with the passive walking idea.

So is there, you know, how energy efficient are animals?

Okay, there's a great series of experiments by George Lauder at Harvard and Mike Tranifilo at MIT.

They were studying fish swimming in a water tunnel, okay?

And 1 of these, the type of fish they were studying were these rainbow trout, Because there was a phenomenon well understood that rainbow trout, when they're swimming upstream at mating season, they kind of hang out behind the rocks.

And it looks like, I mean, that's tiring work swimming upstream.

Maybe there's something energetically interesting there.

They put in this water tunnel a rock, basically a cylinder that had the same sort of vortex street,

eddies coming off the back of the rock that you would see in a stream.

And they put a real fish behind this and watched how it swims.

And the amazing thing is that if you watch from above what the fish swims when it's not behind a rock, it has a particular gate.

You can identify the fish the same way you look at a human walking down the street.

You sort of have a sense of how human walks, the fish has a characteristic gait.

You put that fish behind the rock, its gait changes.

And what they saw was that it was actually resonating and kind of surfing between the vortices.

Now, here was the experiment that really was the clincher, because there was still, it wasn't clear how much of that was mechanics of the fish, how much of that is control, the brain.

So the clincher experiment, and maybe 1 of my favorites to date, although there are many good experiments.

They took a dead fish, they put a string that went, that tied the mouse of the fish to the rock so it couldn't go back and get caught in the grates.

And then they asked what would that dead fish do when it was hanging out behind the rock?

And so what you'd expect, it sort of flopped around like a dead fish in the vortex wake until something sort of amazing happens.

The dead fish basically starts swimming upstream, right?

It's completely dead, no brain, no motors, no control, but it somehow, the mechanics of the fish resonate with the vortex street and it starts swimming upstream.

Is that just evolution constantly just figuring out by killing a lot of generations of animals, like the most efficient motion?

Is that, or maybe the physics of our world completely, is evolution applied not only to animals, but just the entirety of it somehow drives to efficiency?

I don't know if that question even makes any sense.

Yeah, somehow co, yeah, like, I don't know if an environment can evolve, but.

there are experiments that people do, careful experiments that show that animals can adapt to unusual situations and recover efficiency.

So there seems like at least in 1 direction, I think there is reason to believe that the animal's motor system and probably its mechanics adapt in order to be more efficient.

But efficiency isn't the only goal, of course.

Sometimes it's too easy to think about only efficiency.

But we have to do a lot of other things first, not get eaten, And then all other things being equal, try to save energy.

By the way, let's draw a distinction between control and mechanics.

I mean, I think part of the point is that we shouldn't draw a line as clearly as we tend to.

But on a robot, we have motors and we have the links of the robot, let's say.

If the motors are turned off, the robot has some passive dynamics.

You can put springs, I would call that mechanics, right?

If we have springs and dampers, which our muscles are springs and dampers and tendons.

But then you have something that's doing active work, putting energy in, which are your motors on the robot.

The controller's job is to send commands to the motor that add new energy into the system.

So the mechanics and control interplay somewhere.

The divide is around, you know, did you decide to send some commands to your motor or did you just leave the motors off, let them do their work?

So would you say is most of nature on the dynamic side or the control side?

So like if you look at biological systems, or if you know, we're living in a pandemic now, Like do you think a virus is a, do you think it's a dynamic system or is there a lot of control, intelligence?

I think it's both, but I think we maybe have underestimated how important the dynamics are, right?

I mean, even our bodies, the mechanics of our bodies, certainly with exercise, they evolved.

But so I actually, I lost a finger in early 2000s and, it's my fifth metacarpal.

It turns out you use that a lot, in ways you don't expect when you're opening jars.

Even when I'm just walking around, if I bump it on something, there's a bone there that was used to taking.

Contact my fourth metacarpal wasn't used to taking contact, it used to hurt, still does a little bit, but actually my bone has remodeled, right?

Over a couple years, the geometry, the mechanics of that bone changed to address the new circumstances.

So the idea that somehow it's only our brain that's adapting or evolving is not right.

Maybe sticking on evolution for a bit, because it's tended to create some interesting things.

Do you, Why the heck did evolution give us, I think we're, are we the only mammals that walk on 2 feet?

No, I mean, there's a bunch of animals that do it a bit.

I think we are the most successful bypass.

I think I read somewhere that the reason the evolution made us walk on 2 feet is because there's an advantage to being able to carry food back to the tribe or something like that.

So like you can carry, it's kind of this communal, cooperative thing, so like to carry stuff back to a place of shelter and so on to share with others.

Do you understand at all the value of walking on 2 feet from both a robotics and a human perspective?

Yeah, there are some great books written about evolution of, walking evolution of the human body.

I think it's easy though to make bad evolutionary arguments.

Most of them are probably bad, but what else can we do?

I mean, I think a lot of what dominated our evolution probably was not the things that worked well sort of in the steady state, you know, when things are good.

But for instance, people talk about what we should eat now because our ancestors were meat eaters or whatever.

But probably, you know, the reason that 1 pre-homo sapien species versus another survived was not because of whether they ate well when there was lots of food.

But when the ice age came, you know, probably 1 of them happened to be in the wrong place.

1 of them happened to forage a food that was okay even when the glaciers came or something like that.

there's a million variables that contributed and we can't, and are actually the amount of information we're working with in telling these stories, these evolutionary stories is very little.

So yeah, just like you said, it seems like, if we study history, it seems like history turns on like these little events that otherwise would seem meaningless, but in the grant, like when you, in retrospect, were turning points.

And that's probably how, Like somebody got hit in the head with a rock because somebody slept with the wrong person back in the cave days and somebody get angry and that turned, you know, warring tribes can combine with the environment, all those millions of things and the meat eating, which I get a lot of criticism because I don't know what your dietary processes are like, but these days I've been eating only meat, which is, there's a large community of people who say, yeah, probably make evolutionary arguments and say you're doing a great job.

There's probably an even larger community of people, including my mom, who says it's deeply unhealthy, it's wrong, but I just feel good doing it.

But you're right, these evolutionary arguments can be flawed, but is there anything interesting to pull out for folk walking?

There's a great book, by the way, well a series of books by Nicholas Taleb about fooled by randomness and black swan.

Highly recommend them, but yeah, they make the point nicely that probably it was a few random events that, yes, maybe it was someone getting hit by a rock, as you say.

That said, do you think, I don't know how to ask this question or how to talk about this, but there's something elegant and beautiful about moving on 2 feet.

Obviously biased because I'm human, but from a robotics perspective too, you work with robots on 2 feet.

Is it all useful to build robots that are on 2 feet as opposed to 4?

I think the most, I mean the reason I spent a long time working on bipedal walking was because it was hard.

And it challenged control theory in ways that I thought were important.

I wouldn't have ever tried to convince you that you should start a company around bipeds or something like this.

There are people that make pretty compelling arguments, right?

I think the most compelling 1 is that the world is built for the human form.

And if you want a robot to work in the world we have today, then, you know, having a human form is a pretty good way to go.

There are places that a biped can go that would be hard for other form factors to go, even natural places.

But, you know, at some point in the long run, we'll be building our environments for our robots probably, and so maybe that argument falls aside.

Do you wanna make an evolutionary argument for why running barefoot is advantageous?

What have you learned about human and robot movement in general from running barefoot?

Well you know it happened the other way, right?

So I was studying walking robots and I was, there's a great conference called the dynamic walking conference, where it brings together both the biomechanics community and the walking robots community.

And so I had been going to this for years and hearing talks by people who study barefoot running and other, the mechanics of running.

The other thing I had going for me is actually that I, I wouldn't, I wasn't a runner before and I learned to run after I had learned about barefoot running, or I mean started running longer distances so I didn't have to unlearn.

And I'm definitely, I'm a big fan of it for me, but I'm not going to, I tend to not try to convince other people.

There's people who run beautifully with shoes on and that's good.

It's all about the long term game, right?

So I think it's just too easy to run 10 miles, feel pretty good.

And then you get home at night and you realize, my knees hurt.

If you take your shoes off, then if you hit hard with your foot at all, then it hurts.

You don't like run 10 miles, and then, and then realize you've done something, some damage.

You have immediate feedback telling you that you've done something that's maybe suboptimal and you change your gait.

If I right now, having run many miles barefoot, if I put a shoe on, my gait changes in a way that I think is not as good.

And I think my, my goals for running are to do it for as long as I can into old age, not to win any races.

And so for me, this is a way to protect myself.

Yeah, I think, first of all, I've tried running barefoot many years ago, probably the other way, just reading Born to Run.

But just to understand, because I felt like I couldn't put in the miles that I wanted to, and it feels like running for me, and I think for a lot of people, was 1 of those activities that we do often and we never really try to learn to do correctly.

Like, it's funny, there's so many activities we do every day like brushing our teeth, right?

I think a lot of us, at least me, probably have never deeply studied how to properly brush my teeth, right?

Or wash, as now with a pandemic, or how to properly wash our hands.

We do it every day, but we haven't really studied, like, am I doing this correctly?

But running felt like 1 of those things that it was absurd not to study how to do correctly because it's the source of so much pain and suffering.

I do it because I hate it, but I feel good afterwards.

But I think it feels like You need to learn how to do it properly.

And then I quickly realized that my gait was completely wrong.

I was taking huge steps and landing hard on the heel, all those elements.

And so yeah, from that I actually learned to take really small steps.

I already forgot the number but I feel like it was 180 a minute or something like that.

And I remember I actually just took songs that are 180 beats per minute and then like try to run at that beat.

And just to teach myself, it took, it took a long time.

And I feel like, after a while you've, you learn to run, but you adjust it properly without going all the way to barefoot, but I feel like barefoot is the legit way to do it.

I mean, I think a lot of people would be really curious about it.

Can you, if they're interested in trying, what would you, how would you recommend they start or try or explore?

That's the biggest thing people do is they are excellent runners and they're used to running long distances or running fast and they take their shoes off and they hurt themselves instantly trying to do something that they were used to doing.

I think I lucked out in the sense that I I couldn't run very far when I first started trying.

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Russ Tedrake: Underactuated Robotics, Control, Dynamics and Touch | Lex Fridman Podcast #114