Many of today's underwater robots need to periodically come up to the surface to communicate with their human supervisors. But researchers at the University of Washington (UW) have developed a new kind of underwater vehicle. The Robofish can work cooperatively with each other. 'The Robofish, which are roughly the size of a 10-pound salmon, look a bit like fish because they use fins rather than propellers.' According to the researchers, such robots 'could cooperatively track moving targets underwater, such as groups of whales or spreading plumes of pollution, or explore caves, underneath ice-covered waters, or in dangerous environments where surfacing might not be possible.' But read more...
You can see above a team of UW autonomous fin-actuated underwater vehicles. (Credit: UW Nonlinear Dynamics and Control Lab) "Currently, the robots are communicating with full-wave and half-wave wire antennas mounted externally to eliminate any radio loss incurred as a result of an air-water interface. The communication protocol currently implements a straight serial pass-through with Manchester (bi-phase) coding. A software state machine is used to continuously decode the output of the receiver, capturing any valid data and outputting it to the serial port."
And above is a side view of the RoboFish 2.0. (Credit: UW Nonlinear Dynamics and Control Lab) Please note the red acoustic modem on the top of the robot. Here is a link to a larger version of this photograph.
Finally, you can see above an inside view of the RoboFish. (Credit: UW Nonlinear Dynamics and Control Lab) as you can notice, the side panels are removable for easy access to electronics. Here is a link to a larger version of this photograph.
This research project has been led by Kristi Morgansen, a UW assistant professor of aeronautics and astronautics in charge of the Nonlinear Dynamics and Control Lab (NDCL). She worked with UW doctoral students Daniel Klein and Benjamin Triplett who are members of her lab. She also collaborated with UW graduate student Patrick Bettale in electrical engineering and Julia Parrish, an associate professor in the UW's School of Aquatic and Fishery Sciences.
So how did all the researchers found a way to coordinate the movements of the robots? According to the UW article, they faced "major challenges in having robots transmit information through dense water. [...] The energy required to send the information over long distances is prohibitive because the robots have limited battery power. What's more, signals can become garbled when they reflect off the surface or off of any obstacles. Messages were sent between the robots using low-frequency sonar pulses, or pressure waves. The new results showed that only about half the information was received successfully, yet because of the way the Robofish were programmed they were still able to accomplish their tasks. Robots that can independently carry out two simple sets of instructions -- swimming in the same direction or swimming in different directions -- will allow them to carry out more complicated missions."
You'll find more details about the Robofish by looking at the NDCL research projects. Here is an excerpt about the "Fin Actuated Autonomous Underwater Vehicles" project. "Inspired by nature, our intent is to generate novel bio-inspired systems that can out-perform existing engineered systems in speed, agility and efficiency. We focus on bioinspired actuators (based on fish-fin type structures) to control fluid dynamic artifacts (both in and away from the boundary layer) that will ultimately affect speed, agility, and stealth of air and underwater autonomous vehicles. Many underwater vehicles use propellers: propellers provide high thrust, high drag, and low maneuverability. Vehicles using a fish-tail type system are more maneuverable, have the potential to turn in much shorter and more constrained spaces, to have lower drag, to be quieter, and to be more efficient."
For your viewing pleasure, this specific page about Fin Actuated Autonomous Underwater Vehicle carries additional details including videos and photos which I've picked for this post.
But for more technical information, you can browse the impressive NDCL list of publications. Here is my selection of two papers worth reading. The first one has been published in IEEE Transactions on Robotics under the name "Geometric methods for modeling and control of free-swimming fin-actuated underwater vehicles" (Volume 23, Issue 6, Pages 1184-1199, December 2007). Here are two links to the abstract and to the full paper (PDF format, 15 pages, 775 KB).
The second paper is named "Autonomous Underwater Multivehicle Control with Limited Communication: Theory and Experiment" and was included in the Proceedings of the Second IFAC Workshop on Navigation, Guidance and Control of Underwater Vehicles (NGCUV 2008), which was held in Killaloe, Ireland, in March, 2008. Here is a link to this paper (PDF format, 6 pages, 294 KB), from which the top image in this post has been extracted.
Sources: Hannah Hickey, University Week, Vol. 25, No. 30, University of Washington, June 5, 2008; and various websites
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