Coming to Coral Reefs 2: Jelly Bots

Picture: Universities of Southampton & Edinburgh.

Two days ago DIVERNET reported on “Bluebot” robotic fish as a means of carrying out environmental monitoring of coral reefs. Now we have news of another robotic approach to working in fragile underwater environments such as reefs or archaeological sites – based not on schools of fish but on “pulse-jet” animals such as jellyfish and squid.

Unlike the US-designed Bluebot, this invention was produced in Britain, by scientists at the Universities of Southampton and Edinburgh. Based on the shape and movement of the common jellyfish (Aurelia aurita), and on cephalopods such as squid and octopuses, the robot is lightweight and has a soft, flexible exterior.

In terms of their ratio of power to speed and weight the jellyfish is the most efficient animal in Nature. Despite its lack of a supportive skeletal structure it easily beats running and flying animals and bony fish, say the scientists.

The robot propels itself under water using “resonance”, large vibrations that occur when applying a force at the ideal frequency. In this way it uses minimal power to generate the large water jets that push it forward.

The mechanism consists of a rubber membrane enclosing eight 3D-printed flexible ribs to form a “propulsive bell”.

A small piston in the top half of the robot taps the bell repeatedly so that it expands and then springs back, mimicking a jellyfish’s swimming technique and producing the water jets.

Operating at the optimal frequency the robot can, like a jellyfish, cover one body length per second. This makes it 10-50 times more efficient than typical small prop-powered underwater vehicles.

24 January 2021

“Previous attempts to propel underwater robots with jetting systems have involved pushing water through a rigid tube, but we wanted to take it further so we brought in elasticity and resonance to mimic biology, and designed and built the robot in a matter of months,” said the study’s co-author Thierry Bujard from Southampton.

“I was confident that the design would work but the efficiency of the robot was much greater than I expected.”

The team now hope to use the breakthrough to produce a fully manoeuvrable and autonomous underwater robot capable of sensing and navigating in its environment. Their study is published in the journal Science Robotics.