[Editors] MIT unveils robotic clam

[Jen Hirsch]

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RoboClam could lead to “smart” anchors, more
--Research behind device sheds light on real animal’s behavior
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For Immediate Release
MONDAY, NOV. 24, 2008

Contact: Jen Hirsch, MIT News Office
E: jfhirsch at mit.edu, T: 617-253-1682

Photo and Video Available

CAMBRIDGE, Mass. -- The simple razor clam has inspired a new MIT robot  
that could lead to a “smart” anchor that burrows through the ocean  
floor to reposition itself and could even reverse, making it easier to  
recover.

The RoboClam is being developed to explore the performance  
capabilities of clam-inspired digging, as well as to shed light on the  
behavior of the real animal.

“Our original goal was to develop a lightweight anchor that you could  
set then easily unset, something that’s not possible with conventional  
devices,” said Anette “Peko” Hosoi, an associate professor in the  
Department of Mechanical Engineering whose collaborators on the work  
are Amos Winter, a graduate student in her lab, and engineers at  
Bluefin Robotics Corp.

Such devices could be useful, for example, as tethers for small  
robotic submarines that are routinely repositioned to monitor  
variables like currents and temperature. Further, a device that can  
burrow into the seabed and be directed to a specific location could  
also be useful as a detonator for buried underwater mines.

Winter presented the team’s latest results Nov. 23 at a meeting of the  
American Physical Society.

For several years Hosoi’s research has focused on novel propulsion  
mechanisms inspired by nature. So when faced with the anchor problem,  
“We thought, ‘is there an animal that’s well adapted to moving through  
sediments on the seafloor?’”

The first stage of the research, said Winter, involved “looking at all  
the organisms I could find that dig into the ocean bottom, stick to it  
or cling to it mechanically.”

He found what the researchers dub the Ferrari of underwater diggers:  
the razor clam. The animals, about seven inches long by an inch wide,  
“can go about a centimeter a second, so you have to dig fast to catch  
them,” said Winter, who became a licensed clam digger as a result of  
the research.

Another reason why razors make a good model for novel anchors: they  
can dig deeply (up to about 70 centimeters). Plus, in a measure of  
anchoring force, or how hard you pull before an anchor rips out of the  
soil, compared to the energy required to embed the anchor, “razor  
clams beat everything, including the best anchors, by at least a  
factor of 10,” Winter said.

Research subject in hand, one of the team’s first tests gave  
perplexing results. They pushed a clam shell cast in epoxy into “sand”  
composed of glass beads, and compared the amount of force necessary to  
do so to what the living animal is capable of. They found a major  
discrepancy between the two.

“They’re much too weak to do what they do,” Hosoi said. “So we knew  
they were doing something tricky.”

To find out what, Winter created a glass-sided box filled with water  
and beads, added a living clam, and watched the animal burrow. It  
turns out to be a multi-step process. The animal’s tongue-like “foot”  
wiggles down into the sand, then the animal makes a quick up-and-down  
movement accompanied by opening and closing its shell. Together these  
movements propel it.

By filming the movement of the beads, Winter made a startling  
discovery. The clam’s quick up-and-down, opening-and-closing movements  
turn the waterlogged “sand” around it into a liquid-like quicksand.  
Experiments showed that “moving through a fluidized substrate [the  
quicksand] rather than a packed granular medium [ordinary sand]  
drastically reduces the drag force on the clam’s body, bringing it to  
a point within the animal’s strength capabilities,” Winter will report  
Nov. 23.

Over the past summer, Winter completed the RoboClam itself. Although  
only about the size of a lighter, it is supported by a large apparatus  
of pressure regulators, pistons and more that control such things as  
how hard the robot is pushed in each direction.

“Right now we’re getting it up and running” for tests, Winter said.  
Among them, “we want to use RoboClam to verify the theory we’ve  
generated to describe how to dig like a clam.”

This work was sponsored by Bluefin, Battelle, and Chevron.

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By Elizabeth Thomson, MIT News Office
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