IEEE Spectrum - North American - March 2017 - 42

Octopus Locomotion

Attaching [red]
Detaching [blue]

Elongating [red]
Shortening [blue]

Detaching [red]
Attaching [blue]

Shortening [red]
Elongating [blue]

STEP BY STEP: Studying the octopus's crawling technique reveals a four-stage process, which roboticists can copy to design
octo-bots that scoot along the seafloor. First the animal attaches one arm to a firm surface, then it elongates that arm to push its
body forward, then it detaches the limb from the surface, and finally the octopus shortens the arm so it catches up with the body.

ters, which could lead to better control strategies. A team
of researchers at the Worcester Polytechnic Institute, in
Massachusetts, is addressing just that challenge by embedding proprioceptive sensors in a robotic snake.
It's fun to imagine how an advanced robot octopus with
eight dexterous arms could perform in the wild. Take the
marine-energy industry, where there's interest in placing
tidal turbines on the seabed to harvest power from flowing
water. If the machinery breaks, repairs would be difficult
and expensive: Workers would have to haul turbines up to
the surface or send human divers down. Maybe, one day,
an octo-bot technician could be sent instead. With its agile
limbs, it could manipulate tools and make the fix.

We roboticists aren't interested in
the octopus for its limbs and muscles
alone-we also value its particular
brand of intelligence. The octopus's
brain and peripheral nervous system
are well developed compared with
those of other mollusks, but they're still fairly limited.
It's surprising, then, that they can control a huge range
of movements in eight independent arms. So our next
challenge under the Octopus project was to study the
animal's control mechanisms, looking for ways to manage a flexible robot's complex movements.
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MAR 2017

NoRth AMeRicAN

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Biologists have determined that the octopus's brain
doesn't issue top-down commands for every small movement of its twisty limbs. In Octopus vulgaris, the common
octopus, the brain actually contains far fewer neurons
than the peripheral nervous system. Biologists believe
that the brain initiates motions, while lower motor centers
control the precise neuromuscular activity. Experiments
have shown that even if you sever the nerves descending from an octopus's brain, its arms can still recoil from
unpleasant stimuli and reach out as if to grab something.
And here's what we found even more interesting: The
octopus's limbs don't need comprehensive directions to
produce the desired movement. Thanks to millions of
years of evolution, their bodies are designed to respond to
their environment in certain automatic and useful ways.
This concept is often called morphological computation
by roboticists, while artificial intelligence researchers
refer to it as embodied intelligence.
When translated to the robot world, this principle means
we should design our robots so that the physical properties
of their bodies automatically produce the desired movements. With this strategy, extremely simple commands
can cause a robot to efficiently carry out complex tasks.
My team, including my colleague Marcello Calisti and
others, kept this principle in mind when we first set out
to make a robot octopus that could crawl along the seafloor. We studied the locomotion strategy of the real aniillustration by

James Provost

http://SPectRUM.ieee.oRG

Table of Contents for the Digital Edition of IEEE Spectrum - North American - March 2017