Posted: March 21, 2012 in by John Dilligent
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The Robojelly robotic jellyfish could run forever drawing power from its surroundings


Robojelly – a robot jellyfish called that feeds on water – could aid in underwater search and rescue operations, say its creators.

Researchers at Virginia Tech built Robojelly from materials known as shape-memory alloys, which return to their original shape when bent. Eight moving segments wrapped in carbon nanotubes and coated with a platinum powder replicate the jellyfish’s natural opening-and-closing method of propulsion.

The robot is powered by heat produced from chemical reactions between the oxygen and hydrogen in the water and the platinum powder, which causes the alloys to change shape. “To our knowledge, this is the first successful powering of an underwater robot using external hydrogen as a fuel source,”  says Yonas Tadesse, who led the research, published in the journal Smart Materials and Structures today.

More work is needed to make the hydrogen-powered robot fully functional, however. The video above shows an electricity-powered Robojelly swimming freely in a tank of water, but the hydrogen-powered version has so far only been tested while clamped to the bottom of the tank. The researchers’ next step is to figure out a way to deliver hydrogen to each segment separately, allowing them to be controlled individually, so that the robot can move in different directions.


Technical Overview

Artificial muscles powered by a renewable energy source are desired for joint articulation in bio-inspired autonomous systems. In this study, a robotic underwater vehicle, inspired by jellyfish, was designed to be actuated by a chemical fuel source.

The fuel-powered muscles presented in this work comprise nano-platinum catalyst-coated multi-wall carbon nanotube (MWCNT) sheets, wrapped on the surface of nickel–titanium (NiTi) shape memory alloy (SMA). As a mixture of oxygen and hydrogen gases makes contact with the platinum, the resulting exothermic reaction activates the nickel–titanium (NiTi)-based SMA. The MWCNT sheets serve as a support for the platinum particles and enhance the heat transfer due to the high thermal conductivity between the composite and the SMA. A hydrogen and oxygen fuel source could potentially provide higher power density than electrical sources.

Several vehicle designs were considered and a peripheral SMA configuration under the robotic bell was chosen as the best arrangement. Constitutive equations combined with thermodynamic modeling were developed to understand the influence of system parameters that affect the overall actuation behavior of the fuel-powered SMA. The model is based on the changes in entropy of the hydrogen and oxygen fuel on the composite actuator within a channel.

The specific heat capacity is the dominant factor controlling the width of the strain for various pulse widths of fuel delivery. Both theoretical and experimental strains for different diameter (100 and 150 µm) SMA/MWCNT/Pt fuel-powered muscles with dead weight attached at the end exhibited the highest magnitude under 450 ms of fuel delivery within 1.6 mm diameter conduit size. Fuel-powered bell deformation of 13.5% was found to be comparable to that of electrically powered (29%) and natural jellyfish (42%).




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