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Interviewee: Kristi Morgansen,University of Washington
In what amounts to a small swimming pool in the basement of a building on the University of Washington campus, a graduate student is steering a radio-controlled toy shark along the bottom of the pool. Above and behind the toy, three robots that look and act surprisingly like fish are tracking the toy. No one is controlling the “Robofish” — they’re tracking the toy shark all on their own.
“There’s no human directly telling them what to do,” explains Kristi Morgansen, UW assistant professor of aeronautics and astronautics. She adds that, “They have a program on board and they’re getting various sensor information, either from their on-board sensors or stuff that’s transmitted over a wireless channel.”
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Cameras at the corners of the pool, along with computers, feed coordinates that tell the fish their locations and the location of the shark. Morgansen says this is a temporary step and that, “Longer term, what will likely happen is we’ll put more complicated sensors onto them to have them find their own way."
The “Robofish” are essentially self-propelled underwater computers. They belong to a group of devices known as autonomous underwater vehicles, or AUVs. While AUVs have been around for a while and have been used for things like clearing harbors of underwater mines, these Robofish are unique because they are designed to work as a group — a “school” of mechanical fish.
“Fin-essing” the Design
What also jumps out is that these robots are propelled differently. Instead of a propeller, these “fish” have mechanical “fins.” The rear fin flaps back and forth, causing the Robofish to look somewhat like a fish swimming through the water. Fins in the front can tilt to control depth, or flap to propel the fish forward.
Morgansen says the design mimics some of the advantages nature has given fish, explaining, “You don’t have the problems of getting caught in things like kelp or rope or fishing line or things like that, simply because you don’t have something winding.” Additionally, she notes that, “Fish are much more maneuverable in small spaces than things that we’ve been able to build in engineering with propellers."
Since its hard enough to keep one underwater robot working, why try for three or even more? Morgansen explains, “These vehicles would be used for … doing data collection or tracking things in the ocean, making maps, doing inspections around docks or things like that.” So, just like with people, the more you have working together, the better the information and the faster the information gets gathered. In tracking something, like a migrating whale, having multiple observations would result in more accurate readings of the whale’s location or depth.
Results of the initial robot design were presented at a conference on underwater robotics. Since then, the robots have been upgraded to include more complex on-board memory, as well as things like Bluetooth communication to allow the researchers to change the programming without opening the Robofish back up.
Using robots underwater has always posed special challenges. Since water quickly absorbs radio signals, underwater robots have previously been either autonomous or tethered, which limits the ‘bot’s range and mobility.
But Morgansen wanted these robots to be both autonomous, and able to work together. To do this, Morgansen says, “We use a lower frequency transceiver for the vehicles to talk to each other when they’re doing their tasks.” These lower frequencies are below that of AM radio and well below the frequencies used with typical radio controlled airplanes. While water, especially salty seawater, dampens all radio frequencies, lower frequencies are less subject to this dampening effect.
These prototype Robofish are mostly made from off-the-shelf parts. Morgansen says the fins are powered by “standard hobby-shop servos” and the batteries are also something that could be found in a hobby-shop. The body is mostly aluminum, while the fins are Styrofoam coated with fiberglass.
Research on this project was presented at the 2008 International Federation of Automatic Control’s Workshop on Navigation, Guidance and Control of Underwater Vehicles. It was funded by the National Science Foundation and the Air Force Office of Scientific Research.
Elsewhere on the Web:
Association for Unmanned Vehicle Systems International
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