Video: The artificial fish share information on the direction they are swimming in to let all three school together (Footage courtesy Washington University)
Robotic fish with flapping fins and tails have been programmed to swim in a school by researchers at the University of Washington in Seattle. They say that artificial fish with group behaviour could track marine pollutants or wildlife such as whales.
"With a group of vehicles you can get more data collection at the same time than with just one. You get better spatial distribution and cover more area," says Kristi Morgansen, a roboticist at the University of Washington in Seattle, US.
Artificial fish have been on the wish lists of oceanographers and the military for years. It is hoped that mimicking nature's propulsion methods could allow vehicles to be more efficient and manoeuvrable, and deploying them in shoals would allow more complex missions.
But coordinating robots underwater is difficult, not least because radio signals travel badly in water. Previous trials have relied on robots periodically surfacing to receive new orders from a central controller, or being linked by cables.
Instead, Morgansen and colleagues' fish are more independent - controlling and coordinating their own actions, just like real fish do. Currently restricted to a test tank, fish use radio only over short distances.
So far, the team's shoals can only consist of three fish, either swimming in close formation where they all take the same heading, or dispersing to cover as wide an area as possible.
Each robot fish weighs 3 kilograms (6.6 pounds) and measures a half meter long (around 20 inches). A tail provides propulsion, along with two pectoral fins which also steer. These combine to let the fish swim in any direction, make tight turns and even go backwards.
Each fish has an onboard computer, depth sensor, and compass, as well as a radio transceiver. During the experiment, the three broadcast their headings to each other, and used any information received to adjust their own courses.
Morgansen says that the group remained coordinated despite about half of all information packets being lost - showing that the system is relatively robust.
Eventually, the same technique could allow schools of swimming robots to spread out and track a pollution spill, or to report the location of whales or other marine life being studied, Morgansen says.
But communicating over longer distances underwater using radio is difficult or impossible. Acoustic modems that use sonar-like "pings" to communicate are suitable, though. That kind of set-up will be installed on another University of Washington underwater robot, called Seaglider, to allow schooling trials in the open ocean.
Eventually, Morgansen says, she hopes to build more robust versions of the fin-driven robots and test them in open water as well.
Scott David Kelly at the University of Illinois at Urbana-Champaign, US, works on the mechanics underlying natural and artificial fish propulsion. He says Morgansen's research is unusual because she has combined a good understanding of hydrodynamics, robotics, and coordinated motion control in her work.
External link: http://www.newscientist.com/article/dn14101