Robotic ghost knifefish is born (w/ Video)

Jan 19, 2011 By Megan Fellman

(PhysOrg.com) -- Researchers at Northwestern University have created a robotic fish that can move from swimming forward and backward to swimming vertically almost instantaneously by using a sophisticated, ribbon-like fin.

The -- created after observing and creating of the black ghost knifefish -- could pave the way for nimble robots that could perform underwater recovery operations or long-term monitoring of coral reefs.

Led by Malcolm MacIver, associate professor of mechanical and at Northwestern’s McCormick School of Engineering and Applied Science, the team’s results are published in the Journal of the Royal Society Interface.

The black ghost knifefish, which works at night in rivers of the Amazon basin, hunts for prey using a weak electric field around its entire body and moves both forward and backward using a ribbon-like fin on the underside of its body.

MacIver, a robotics expert who served as a scientific consultant for “Tron: Legacy” and is science advisor for the television series “Caprica,” has studied the knifefish for years. Working with Neelesh Patankar, associate professor of mechanical engineering and co-author of the paper, he has created mechanical models of the fish in hopes of better understanding how the nervous system sends messages throughout the body to make it move.

Planning for the robot -- called GhostBot -- began when graduate student Oscar Curet, a co-author of the paper, observed a knifefish suddenly moving vertically in a tank in MacIver’s lab.

“We had only tracked it horizontally before,” said MacIver, a recent recipient of the prestigious Presidential Early Career Award for Scientists and Engineers. “We thought, ‘How could it be doing this?’”

Further observations revealed that while the fish only uses one traveling wave along the fin during horizontal motion (forward or backward depending on the direction on the wave), while moving vertically it uses two waves. One of these moves from head to tail, and the other moves tail to head. The two waves collide and stop at the center of the fin.

The team then created a computer simulation that showed that when these “inward counterpropagating waves” are generated by the fin, 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,” MacIver said.

The group then hired Kinea Design, a design firm founded by Northwestern faculty that specializes in human interactive mechatronics, and worked closely with its co-founder, Michael Peshkin, professor of mechanical engineering, to design and build a robot. The company fashioned a forearm-length waterproof robot with 32 motors giving independent control of the 32 artificial fin rays of the lycra-covered artificial fin. (That means the robot has 32 degrees of freedom. In comparison, industrial robot arms typically have less than 10.) Seven months and $200,000 later, the GhostBot came to life.

The group took the robot to Harvard University to test it in a flow tunnel in the lab of George V. Lauder, professor of ichthyology and co-author of the paper. The team measured the flow around the by placing reflective particles in the water, then shining a laser sheet into the water. That allowed them to track the flow of the water by watching the particles, and the test showed the water flowing around the biomimetic robot just as computer simulations predicted it would.

“It worked perfectly the first time,” MacIver said. “We high-fived. We had the robot in the real world being pushed by real forces.”

The robot is also outfitted with an electrosensory system that works similar to the knifefish’s, and MacIver and his team hope to next improve the robot so it can autonomously use its sensory signals to detect an object and then use its mechanical system to position itself near the object.

Humans excel at creating high-speed, low-maneuverability technologies, like airplanes and cars, MacIver said. But studying animals provides a platform for creating low-speed, high-maneuverability technologies -- technologies that don’t currently exist. Potential applications for such a robot include underwater recovery operations, such as plugging a leaking oil pipe, or long-term monitoring of oceanic environments, such as fragile coral reefs.

While the applied work on the robot moves ahead in the lab, the group is pursuing basic science questions as well. “The robot is a tool for uncovering the extremely complicated story of how to coordinate movement in animals,” MacIver said. “By simulating and then performing the motions of the fish, we’re getting insight into the mechanical basis of the remarkable agility of a very acrobatic, non-visual fish. The next step is to take the sensory work and unite the two.”

Explore further: Telerobotics puts robot power at your fingertips

More information: rsif.royalsocietypublishing.org/

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User comments : 7

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antialias
5 / 5 (2) Jan 19, 2011
Next they should see how efficient such a propulsion system would be.

The thing I like most about this compared to propellers on regular subs or boats: You can't jam a fin like this with debris or get a cable stuck in them. This would make them ideal for difficult terrain or high risk environments where propulsion must not fail.
sstritt
5 / 5 (1) Jan 19, 2011
Also could have acoustic stealth applications for the navy- no cavitation from props.
Mercury_01
not rated yet Jan 19, 2011
Did anyone else think this rig was overly complicated? Why use pulleys and belts to move such small angles? Why not solenoids or electronic muscle fibers?
gwrede
not rated yet Jan 19, 2011
Did anyone else think this rig was overly complicated? Why use pulleys and belts to move such small angles? Why not solenoids or electronic muscle fibers?
Solenoids are more complicated to control accurately, and muscle fibers are too expensive for their budget? This was a quick-and-cheap experiment, like a proof of concept. I bet showing this gives them funding for a much better one.
dinkster
not rated yet Jan 19, 2011
Right off the bat, I see a military application for a very, very, quiet submarine propulsion system. If this could propel a sub as fast as a prop in full thrust without any of the micro bubble sonar noise, fantastic!
ekim
not rated yet Jan 19, 2011
Did anyone else think this rig was overly complicated? Why use pulleys and belts to move such small angles? Why not solenoids or electronic muscle fibers?

Hydraulics would also work well. Alternating pressure in two reservoirs running down each side combined with some switches opening valves on each ray.
antialias
5 / 5 (1) Jan 20, 2011
This looks like a typical PhD project. While all of the alternative actuator methods mentioned are valid you have to understand under what kinds of constraints such projects are under:

1) tight budget
2) tight timeline
3) you don't know whether it's even going to work (this is research, not enineering)

Under such conditions you go with the simplest/cheapes approach first. After the feasibility has been demonstrated you (i.e. the next PhD student) can make an improved prototype.