Innovative anchor takes inspiration from the Ferrari of underwater diggers
By Darren Quick
November 23, 2009
Researchers at MIT have taken inspiration from the simple razor clam to design a “smart” anchor that burrows through the ocean floor. The so-called RoboClam could prove useful as tethers for small robotic submarines that are routinely repositioned to monitor variables such as currents and temperatures. The device can burrow into the seabed, be directed to a specific location and can also operate in reverse, making them easier to recover.
According to researcher Anette (Peko) Hosoi, an associate professor in the MIT Department of Mechanical Engineering, "the best anchoring technology out there is an order or magnitude worse than the clam - most are two or three orders worse."
Using relatively simple anatomy, the clam burrows into the bottom of its native mudflats at a rate of a centimeter per second. Hosoi's studies of the physics behind this remarkable ability have revealed that the digging is accomplished in two motions - a push upwards with its foot, which mixes the grains of solid into the liquid above, and a synchronized push down. The team discovered that the clam’s quick up-and-down, opening-and-closing movements turn the waterlogged sand around it into a liquid-like quicksand.
By borrowing this principle, Hosoi and graduate student Amos Winter have created a simple robot that is now being tested out in the salt water mudflats off of Cape Cod. The robot is operated electronically via a tether and is made to open and close via pressured air from a scuba tank. It digs just as fast as the living clam and is "small, lightweight, and does not use a lot of energy," says Hosoi.
Aside from making a more secure anchor the RoboClam could also be useful as a detonator for buried underwater mines.
The MIT researchers chose the razor clam, which is dubbed the Ferrari of underwater diggers, not only because of its speed, but also because it can dig deeply – up to about 70 cm (27.5-inches). Plus, in a measure of anchoring force, or how hard you pull before an anchor rips out the soil compared to energy required to embed the anchor, “razor clams beat everything, including the best anchors, by at least a factor of 10," Winter said.