Robots mimic razor clams
MIT researchers have developed a robot inspired by the razor clam. According to the engineers, this RoboClam could lead to a 'smart' anchor that burrows through the ocean floor to reposition itself and could even reverse. These small robots, which have the size of a cigarette lighter, could be used as 'tethers for small robotic submarines that are routinely repositioned to monitor variables such as currents and temperature. [They also could] be directed to a specific location could also be useful as a detonator for buried underwater mines.' But read more...
You can see above a picture of the MIT's RoboClam close to a real razor clam. "Inspired by the amazing ability of the small clam to dig and wedge itself far deeper and more securely than would be thought, they show the robo-clam, a metal device on the right, anchored in sand in a testing device right next to a razor clam in the sand to the left." (Credit for photo: Donna Coveney, MIT) Here is a link to a larger version of this photo.
This research work has been conducted in the Hatsopolous Microfluids laboratory (HML) by Anette (Peko) Hosoi, an associate professor in the MIT's Department of Mechanical Engineering and her research group including Amos Winter, a graduate student in her lab, and engineers at Bluefin Robotics Corp.
First, what led this team to focus on the razor clam to build a robotic anchor? "The first stage of the research, Winter said, 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.
So the engineers started to study these clams, but they were puzzled by their results. "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 solve this problem, the team decided to film the clams put into glass-sided box filled with water and beads and discovered the secrets of the burrowing clams. '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 reported."
After this discovery, building a robot mimicking the clam by copying this moving system was just an engineering process. "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."
This research work has been presented on November 24, 2008 at the 61st Annual Meeting of the American Physical Society's Division of Fluid Dynamics under the title "Drag reduction mechanisms employed by burrowing razor clams (Ensis directus)." Here is a link to the abstract. "In this work we describe how razor clams use localized fluidization to reduce drag and efficiently burrow through a granular substrate. Razor clams require nearly two orders of magnitude less force to move through sand than a blunt body of the same size and shape. By visualizing substrate deformation during burrowing, we investigate the clamshell kinematics which fluidize a small pocket of substrate around the body of the organism. Through experimentation and scaling arguments, we show that moving through a fluidized substrate rather than a packed granular medium dramatically reduces the drag force on the clam's body to a point within the animal's strength capabilities."
For more information, you also might want to check the following links.
- A movie on Amos Winter site (64 MB)
- Robot Clam Achieves Feat with Foot (Cynthia Graber, 60-Second Science podcast, Scientific American, December 2, 2008)
- To put up an oil rig, follow that clam (Ivan Semeniuk, New Scientist, July 15, 2008)
- Experimental Investigations of Elastic Tail Propulsion At Low Reynolds Number (MIT, 5 pages, 212 KB, August 23, 2006)
Sources: Elizabeth A. Thomson, MIT News Office, November 25, 2008; and various websites
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