A robot that runs and swims like a salamander

This is Pleurobot.

Pleurobot is a robot that we designed
to closely mimic a salamander species

called ??

Pleurobot can walk, as you can see here,

and as you'll see later, it can also swim.

So you might ask,
why did we design this robot?

And in fact, this robot has been designed
as a scientific tool for neuroscience.

Indeed, we designed it
together with neurobiologists

to understand how animals move,

and especially how the spinal cord
controls locomotion.

But the more I work in biorobotics,

the more I'm really impressed
by animal locomotion.

If you think of a dolphin swimming
or a cat running or jumping around,

or even us as humans,

when you go jogging or play tennis,

we do amazing things.

And in fact, our nervous system solves
a very, very complex control problem.

It has to coordinate more
or less 200 muscles perfectly,

because if the coordination is bad,
we fall over or we do bad locomotion.

And my goal is to understand
how this works.

There are four main components
behind animal locomotion.

The first component is just the body,

and in fact we should never underestimate
what extent the biomechanics

already simplify locomotion in animals.

Then you have the spinal cord,

and in the spinal cord you find reflexes,

like multiple reflexes that create
a sensory motor coordination loop

between neural activity in the spinal cord
and mechanical activity.

A third component
are central pattern generators.

These are very interesting circuits
in the spinal cord of vertebrate animals

that can generate, by themselves, very
coordinated rhythmic patterns of activity

while receiving only
very simple input signals.

And these input signals come from
descending modulation

from higher parts of the brain,
from the motor cortex, the cerebellum,

the basal ganglia, will all modulate
activity of the spinal cord

while we do locomotion.

But what's interesting is to what extent
just a low level component,

the spinal cord, together with the body,
already solves a big part

of the locomotion problem,

and you probably know it by the fact
that you can cut the head of the chicken,

it can still run for a while,

showing that just the lower part,
spinal cord and body,

already solves a big part of locomotion.

Now, understanding how this works
is very complex,

because first of all,

recording activity in the spinal cord
is very difficult.

It's much easier to implant electrodes
in the motor cortex

than in the spinal cord, because
it's protected by the vertebrae.

Especially in humans,
it's very hard to do.

A second difficulty is that locomotion
is really due to a very complex

and very dynamic interaction
between these four components.

So it's very hard to find out
what's the role of each over time.

This is where biorobots like Pleurobot
and mathematical models

can really help.

So what's biorobotics?

Biorobotics is a very active field
of research in robotics

where people want to take inspiration
from animals to make robots

to go outdoors,

like service robots
or search-and-rescue robots

or field robots,

and the big goal here is
to take inspiration from animals

to make robotics that can handle
complex terrain --

stairs, mountains, forests,

places where robots
still have difficulties

and where animals can do
a much better job.

The robot can be
a wonderful scientific tool as well.

There are some very nice projects
where robots are used

like a scientific tool for neuroscience,
for biomechanics, or for ?? dynamics.

And this is exactly
the purpose of Pleurobot.

So what we do in my lab
is to collaborate with neurobiologists

like Jean-Marie Cabelguen,
a neurobiologist in Bordeaux in France,

and we want to make spinal cord models
and validate them on robots.

And here we want to start simple.

So it's good to start with simple animals

like lampreys, which are
very primitive fish,

and then gradually go toward
more complex locomotion,

like in salamanders,

but also in cats and in humans,

in mammals.

And here, a robot becomes
an interesting tool

to validate our models,

and in fact, for me, Pleurobot
is a kind of dream becoming true.

Like, more or less 20 years ago
I was already working on a computer

making simulations of lamprey
and salamander locomotion

during my Ph.D.

But I always knew that my simulations
were just approximations.

Like, simulating the physics in water
or with mud or with complex ground,

it's very hard to simulate that
properly on a computer.

Why not have a real robot
and real physics?

So among all these animals,
one of my favorites is the salamander.

You might as why, and it's because
as an amphibian,

it's a really key animal
from an evolutionary point of view.

It makes a wonderful link

between swimming, as you find it
in eels or fish,

and quadruped motion, as you see
in mammals, in cats and humans.

And in fact, the modern salamander

is very close to the first
terrestrial vertebrate,

so it's almost a living fossil,

which gives us access to our ancestor,

the ancestor to all terrestrial tetrapods.

So the salamander swims by doing
what's using what's called

a ??? swimming gate,

so they propagate a nice traveling wave
of muscle activity from head to tail.

And if you place the salamander
on the ground,

it switches to what's called
a walking trot gate.

In this case, you have nice
activation of the limbs

which are very nicely coordinated
with this standing wave undulation

of the body,

and that's exactly the gate
that you are seeing here on Pleurobot.

Now, one thing which is very surprising
and fascinating in fact

is the fact that all this can be generated
just by the spinal cord and the body.

So if you take ?? salamander --

it's not so nice
but you remove the head --

and if you electrically stimulate
the spinal cord,

a low level of stimulation
this will use a walking-like gate.

If you stimulate a bit more,
the gate accelerates,

and at some point, there's a transfer,
and automatically,

the animal switches to swimming.

This is amazing,

just changing the global drive
as if you are pressing the gas pedal

of descending modulation
to your spinal cord,

makes a complete switch
between two very different gates.

And in fact, the same
has been observed in cats.

If you stimulate the spinal cord of a cat,

you can switch between
walk, trot, and gallop.

Or in birds, you can make a bird
switch between walking,

at low levels of stimulation,

and flapping its wings
at high level stimulation.

And this really shows that the spinal cord
is a very sophisticated

locomotion controller.

So we studied salamander locomotion
in more detail,

and we had in fact access
to a very nice x-ray video machine

from Professor Martin Fischer
in Jena University in Germany.

And thanks to that, you really have
an amazing machine

to record all the bone motion
in great detail.

That's what we did.

So we basically figured out
which bones are important for us

and collected their motion in 3D.

And what we did is collect
a whole database of motions,

both on ground and in water,

to really collect the whole database
of motor behaviors

that a real animal can do,

and then our job as roboticists
was to replicate that in our robot.

So we did a whole optimization process
to find out the right structure,

where to place the motors,
how to connect it together,

to be able to replay
these motions as well as possible.

And this is how Pleurobot came to life.

So let's look how closely it is
to the real animal.

So what you see here is almost
a direct comparison

between the walking
of the real animal and the Pleurobot.

You can see that we have almost
A one-to-one exact replay

of the walking gate.

If you go backwards and slowly,
you see it even better.

But even better, we can do swimming.

So for that we have a dry suit
that we put all over the robot --

(Laughter) --

and then we can go in water
and start replaying the swimming gates.

And here, we were very happy,
because this is difficult to do.

The physics of interaction are complex.

Our robot is much bigger
than a small animal,

so we had to do what's called
dynamical scaling of the frequencies

to make sure we had the same
interaction physics.

But you see at the end
we have a very close match,

and we were very, very happy with this.

So let's go do the spinal cord.

So here what we did
with Jean-Marie Cabelguen

is model the spinal cord circuits.

And what's interesting is that
the salamander has kept

a very primitive circuit

which is very similar to the one
we find in the lamprey,

pretty much this eel-like fish,

and it looks like during evolution,

new neuronal oscillators have been added
to control the limbs,

to do the leg locomotion.

And we know where
these neuronal oscillators are

but what we did was to make
a mathematical model

to see how they should be coupled

to allow this transition between
the two very different gates.

And we tested that on board of a robot.

And this is how it looks.

So what you see here

is a previous version of Pleurobot

that's completely controlled
by our spinal cord model

programmed on board of the robot.

And the only thing we do
is send to the robot

through a remote control

the two descending signals
it normally should receive

from the upper part of the brain.

And what's interesting is,
by playing with these signals,

we can completely control
speed, heading, and type of gate.

For instance,

when we stimulate at a low level,
we have the walking gate,

and at some point, if we stimulate a lot,
very rapidly it switches

to the swimming gate.

And finally, we can also do turning

very nicely by just stimulating more one
side of the spinal cord than the other.

And I think it's really beautiful

how nature has distributed control

to really give a lot of responsibility
to the spinal cord

so that the upper part of the brain
doesn't need to worry about every muscle.

It just has to worry about
this high-level modulation,

and it's really the job of the spinal cord
to coordinate all the muscles.

So now let's go to cat locomotion,
and the importance of biomechanics.

So this is another project

where we studied cat biomechanics,

and we wanted to see how much
the morphology helps locomotion.

And we found three important
criteria in the properties,

basically, of the limbs.

The first one is that a cat limb

more or less looks
like a pantograph-like structure.

So a pantograph is a mechanical structure

which keeps the upper segment
and the lower segments always parallel.

So a simple geometrical system
that kind of coordinates a bit

the internal movement of the segments.

A second property of cat limbs
is that they are very lightweight.

Most of the muscles are in the trunk,

which is a good idea, because then
the limbs have low inertia

and can be moved very rapidly.

The last final important property is this
very elastic behavior of the cat limb,

so to handle impacts and forces.

And this is how we designed Cheetah-Cub.

So let's invite Cheetah-Cub onstage.

So this is Peter Eckert,