Fast Company

Robotic Ghost Knifefish Swims in Every Direction, Causes Brainiacs to High-Five [Video]

The robot imitates a bizarre fish with a ribbon-like fin enabling underwater acrobatics.

Researchers at Northwestern University have created a robotic ghost knifefish. It was no small feat: the ghost knifefish has a strange, ribbon-like fin that gives it incredible maneuverability, both horizontally and vertically. GhostBot, as the robot is called, could represent the first step on the road to sophisticated robots that could perform underwater rescues, among other things. The robot and its features are reported in a recent issue of the Journal of the Royal Society Interface (PDF).

The research all began in earnest when one of the scientists involved, Oscar Curet, noticed a real-life knifefish make a sudden, unexpected vertical movement. The fish was in a tank owned by Malcolm MacIver, an engineering professor at Northwestern's McCormick School of Engineering and Applied Science who has also served as a scientific consultant on the movie Tron: Legacy and the TV series Caprica. "We thought, 'How could it be doing this?'" recalled MacIver, according to a press release.

MacIver, Curet, and others studied the fish further. Typically, when moving horizontally, the fish would wiggle its fin one way or the other, thereby moving forward or back. But when it managed to burst upwards, the scientists saw that it did something remarkable. Rather than begin a wave at just one tip of the fin, it would simultaneously begin waves at either end. The waves would then meet in the middle, creating a burst of force that propelled the fish upwards. In the words of the release: "horizontal thrust is canceled and the fluid motion generated by the two waves is funneled into a downward jet from the center of the fin, pushing the body up. The flow structure looks like a mushroom cloud with an inverted jet."

“It’s interesting because you’re getting force coming off the animal in a completely unexpected direction that allows it to do acrobatics that, given its lifestyle of hunting and maneuvering among tree roots, makes a huge amount of sense,” said MacIver.

These were engineers, though, so they weren't content with just describing the motion. They had to recreate it. They collaborated with Kinea Design, a design firm spun off by some Northwestern professors, put up $200,000, and made their very own robotic ghost knifefish. They brought it to a flow tunnel at Harvard for a test run, and it performed beautifully. The ecstatic researchers high-fived each other.

This isn't just fun, though; the researchers think (naturally) that the robot will have some real-world applications, leading to underwater robots with unprecedented maneuverability. New kinds of rescue operations and more sophisticated monitoring of coral reefs could become possible. As MacIver points out, human beings are good at making fast but clumsy devices, like the car (which, after all, doesn't perform very well except when on roads). We're not so good at making slow, pliable, graceful devices, that move with precision. GhostBot is an effort to change that.

[Image: Kinea Design]

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