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Underwater Robots > Robojelly
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Underwater Robots > Robojelly

Robojelly, first created by engineers at Virginia Polytechnic Institute and State University (VirginiaTech) in 2009, is a robot jellyfish that is continuously being upgraded and refined in order to create a robot which moves through the water just like a natural jellyfish – and in so doing, reverse engineer a full understanding of how the jellyfish and other soft-body creatures manage to propel themselves through liquid.

It was originally developed for the US Office of Naval Research, as an underwater surveillance robot, however its capabilities left a great deal to be desired. In the years since, major improvements have been showcased twice, at the 2011 meeting of the American Physical Society’s Division of Fluid Dynamics and in the journal Smart Materials and Structures in early 2012.

The robot is essentially a silicone sheath over a shape memory-alloy core. It uses a gaseous fuel, a mix of oxygen and hydrogen which is consumed to provide the power to contract the nickel-titanium shape memory alloy used to provide the actuators inside the shell, and to provide the propulsion boost when the combusted materials are ejected.

The original robot failed to fully mimic the jellyfish, and engineers were at a loss to explain why. In nature the jellyfish uses the bell section of its body, which deforms and contracts to provide thrust. The lower, or lagging, section of the bell is known as the flexible margin, and it deforms slightly later in the swimming process than the rest of the bell.

In robotics, there was no realistic way of reproducing this effect when the robot was first created. This is the fault that led to rather less than satisfactory performance in 2009. Any attempt to recreate the two-part contraction in an aquatic, soft-body robot failed. Unlike their natural counterparts, the artificial materials tended to fold as they deformed, reducing Robojelly’s performance.

A solution found in 2011 was a paradigm shift. Instead of trying to initiate a second contraction phase in the lower half, a simple solution was to cut slots into the bell itself. Simple fluid dynamics forced the lower half to contract slightly later. The very presence of the water as it forces through the slits is the key to this secondary contraction, rather than the jellyfish's own muscles.

The strokes still aren't exact to an actual jellyfish, but they are a lot closer, and as a side effect, the jellyfish robot's speed is drastically increased.

The U.S. Navy's Office of Naval Research is funding the continued development of Robojelly, and as the design continues to improve, the original dream of using these robots to monitor the state of operations underwater – anything from tracking shoals of fish, to checking for leaks in pipes, to search and rescue from an underwater vector. There are many more military uses for a robot that looks like a jellyfish and swims like a jellyfish, but is able to feed video data back to it's HQ.

References

Robojelly Gets an Upgrade: Underwater robot learns to swim more like the real thing (PDF)

Robotic jellyfish fuelled by hydrogen invented

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