The Japanese spider crab is about to lose its title as the world's largest crustacean thanks to a new robot, the Crabster, developed in South Korea. For the past 2 years, researchers at the Korean Institute of Ocean Science and Technology (KIOST) have been working on a giant robot crab that is about the size and weight of a Smart car. This summer it will help scientists explore wrecks below the sea, weathering harsh tidal currents rushing over it at 1.5 m/s.

One of the key problems associated with traditional propeller-driven underwater remotely-operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) is they don't perform well in strong currents. Another problem is their propellers tend to kick up a lot of detritus, lowering operator visibility. To overcome these problems a team led by Principal Research Scientist Bong-huan Jun of KIOST designed a six-legged robot based on the characteristics of crabs and lobsters (hence the name).

The robot's six legs contain a total of 30 powerful joints. Like its biological cousins, the robot's two front legs are more articulated than the rest so they can be used as arms. Objects can be picked up and stored inside a frontal compartment to be brought to the surface. Even in shallow seas it can get pretty dark down there, so the Crabster is equipped with 10 optical cameras and a long-range scanning sonar which scans up to 200 m (650 ft) away.

The team used computer simulations to streamline the robot's main shell so that it would actually stabilize the robot under the force of the currents. By shifting its posture with its six legs, the body shell effectively reduces drag and increases lifting force. It's a bit like how real crabs stick out their arms to help steady themselves in fast-moving currents.

The Crabster has a frontal compartment for bringing objects to the surface

In about a month the Crabster and its control station will be transported by shipping container to waters off the coast of South Korea. There it will be lowered 200 meters by crane to the sea floor where it will undergo its first real world trials. The goal is to eventually explore historical wrecks and other sites.

It can remain on the sea floor as long as it has power, operating for more than 24 hours at a time through an external power cable. In the future, the researchers would like to cut the cord, and maybe even have the robot swim. They're studying how frogs, turtles, and water beetles propel themselves with their hind legs in the hopes the Crabster can mimic the ability. In the meantime it will simply crawl to get around.

The team started with a much smaller prototype called the Little Crabster, which performed walking tests on treadmills and uneven ground, before building the bigger version. You can see the robots, including a computer animation showing how it is intended to work, in the following videos.

Source: KIOST

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