New robot burrows like a clam using little energy

MIT researchers have developed a robot that mimics the ability of the Atlantic razor clam to burrow into undersea soil at high speed using very little energy.
The device, known as 'RoboClam', could be used to dig itself into the ground to bury anchors or destroy underwater mines, according to its developer, Amos Winter, the Robert N Noyce Career Development Assistant Professor of Mechanical Engineering at Massachusetts Institute of Technology.
Despite its rigid shell, the Atlantic razor clam (Ensis directus) can move through soil at a speed of 1 centimetre per second. The animal is able to dig up to 0.5 kilometres using only the amount of energy contained in a AA battery.

"The clam's trick is to move its shells in such a way as to liquefy the soil around its body, reducing the drag acting upon it," Winter said.
"This means it requires much less force to pull its shell into the soil than it would when moving through static soil," Winter said.
To develop a robot that can perform the same trick, Winter and his co-developer, Anette Hosoi, professor of mechanical engineering and applied mathematics at MIT, needed to understand how the clam's movement causes the soil to liquefy, or turn into quicksand, around its shell.

Now, in a paper to be published in the journal Bioinspiration and Biomimetics, the researchers showed for the first time the mechanics behind this process, and describe how their robot is able to mimic this action.

When the razor clam begins to dig, it first retracts its shell, releasing the stress between its body and the soil around it. This causes the soil to begin collapsing, creating a localised landslide around the animal.
As the clam continues to contract, reducing its own volume, it sucks water into this region of failing soil. The water and sand particles mix, creating a fluidised substrate - quicksand.
However, the timing is crucial. If the clam were to move its shell too slowly, the sand particles would collapse around the animal without fluidising, Winter said.
If the clam moved too quickly, it would not give the sand particles enough time to mix with the water flowing past, and they would simply remain stationary.

To develop a low-energy anchoring system that can create quicksand around itself in this way, the researchers built a mechanical puppet clamshell, consisting of two halves that can move together and apart in a similar way to an accordion.
The puppet clam is connected to a rod, which can open and close the shell and push it up and down, creating the same contractions as the animal can achieve.
To make it easier to test their RoboClam prototype in salt water, the researchers used a compressed air system to power the expansion and contraction of the shells.
In addition to anchoring underwater vehicles and detonating mines, the RoboClam could also be used to lay underwater cables, Winter said.