Of all the animals scientists could try to replicate in robotics, the humble jellyfish would not seem to be on the top of the list. Why not a whale? Or a shark? But a jellyfish’s movement allows it to travel through the water easily, basically silently, and with minimal energy. And so instead of a robotic shark, we have a robotic jellyfish, the Robojelly.
Robojelly could also be called into duty by the U.S. Navy, posing as a stealth surveillance bot in jellyfish camouflage. The floppy bot could also aid scientists as a research tool, unobtrusively watching the ocean—observing fish migrations, following around icebergs—collecting data over extended periods without disturbing the ocean wildlife.
The live moon jellyfish, on which Robojelly is modeled, is a stunningly efficient animal, says bot builder and Virginia Tech graduate student Alex Villanueva. "We looked at the way it moves, swims … our goal was to create a robot to replicate these things."
Robojelly has a rubbery silicone dome that puffs and unpuffs, mimicking the motion of the real live moon jellyfish. The expansion and contraction of the dome is controlled by a heat-sensitive smart material—"They’re wires that look like hair," Villanueva explains—that curl when hot and relax into their original shape when cooled.
The wires, located under the dome, are rigged up to strings that thread their way outward through each of eight sections on the silicone dome. The wires are coated with platinum and carbon nanotubes. When hydrogen and oxygen meet on the wires, the platinum and carbon act as a catalyst, kicking off a reaction that releases heat. When the hot wires contract, they tug at the strings, pulling the ends of the dome inward. And thus, the Robojelly moves through the ocean.
In its first incarnation, Robojelly ran on electricity. A live current would heat up and contract the wires, and Robojelly would puff forward. The new Robojelly runs on hydrogen and oxygen (those two elements are conveniently found in bulk in water). They’re also a better bet, Villanueva explains, because hydrogen is an energy-dense fuel and goes a longer way, making the robot better suited to long, unattended stints in the ocean.
Robojelly will need to be tweaked a tad before it actually hits the surf. The design needs to be compacted, so everything fits under the bell, Villanueva says. There are plans to create a mechanism which will let Robojelly suck in hydrogen and oxygen from the very water it’s swimming in, making it fully energy independent, Villanueva says, but that’s for the far future. For now, it carries its oxygen and hydrogen with it.
When it’s ready, Robojelly will join the ranks of ocean-going bots like the wave-powered Wave Glider, just another robot swimming with the fishes.