Robojelly – a robot inspired by moon jellyfish

Engineers at Virginia Polytechnic Institute and State University (VirginiaTech) have used inspiration from nature and developed a robot whose design and motion patterns resemble moon jellyfish (Aurelia aurita). Named Robotjelly, the robot was developed for the U.S. Office of Naval Research back in 2009, and its latest improved iteration was presented at the 2011 meeting of the American Physical Society.

The natural moon jellyfish uses the bell section of its body to provide thrust by deforming and contracting. The lower section of the bell deforms slightly later in the swimming process than the rest of the bell. Previous version of Robojelly lacked this crucial piece of anatomy in its design, and its artificial materials tended to fold as they deformed.

However, the team from VirginiaTech managed to improve the performance of this silicone swimmer, enabling it to overcome the limitations of its artificial skin and mimic the motion of a real jellyfish more closely. After testing a number of designs and lengths for the folding margin, the team discovered that cutting slots into the bell reduced this unwanted folding effect.

Robojelly looks very similar to an actual jellyfish, with a bell diameter of 164 mm (6.45 inches) and a total mass of 242g (half a pound). Robot’s body is built out of RTV silicone and it uses shape memory alloy (SMA) actuators to swim. These actuators consist of smart materials called shape memory alloy arranged in a way that maximizes deformation. It consumes an average power on the order of 17 W with the actuators not having fully reached a thermal steady state.

Thrust measurements were performed on a natural jellyfish in order to compare those results with different configurations of the robot, and the researchers found that best performing configuration was a Robojelly with segmented bell and a passive flap structure which has a better swimming stroke, as well as a big boost in speed. It managed to perform with nearly 80 percent of its natural counterpart.

“These results clearly demonstrate that the flap plays an important role in the propulsion mechanism of Robojelly and provides an anatomical understanding of natural jellyfish”, said Alex Villanueva, VirginiaTech mechanical engineer.

Robojelly was designed for navy to conduct ocean underwater surveillance where it could monitor the presence of ships and submarines, but it could be used in civic purposes such as underwater chemical spills detection, or in marine life research where it could observe the migration of schools of fish.

Details on this new design and how it might provide new insights into jellyfish propulsion mechanisms were presented at the 2011 meeting of the American Physical Society’s Division of Fluid Dynamics in Baltimore, Maryland.

For more information, read the paper published in the journal Bioinspiration & Biomimetics named: “A biomimetic robotic jellyfish (Robojelly) actuated by shape memory alloy composite actuators”.