[Editors] MIT building robotic fin for submarines

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

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MIT team building robotic fin for submarines
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For Immediate Release
MONDAY, JULY 30, 2007
Contact: Elizabeth A. Thomson, MIT News Office
Phone: 617-258-5402
Email: thomson at mit.edu

VIDEO, PHOTOS AVAILABLE

STORY ONLINE AT: http://web.mit.edu/newsoffice/2007/robofin-0730.html

CAMBRIDGE, Mass--Inspired by the efficient swimming motion of the 
bluegill sunfish, MIT researchers are building a mechanical fin that 
could one day propel robotic submarines.

The propeller-driven submarines, or autonomous underwater vehicles 
(AUVs), currently perform a variety of functions, from mapping the 
ocean floor to surveying shipwrecks. But the MIT team hopes to create 
a more maneuverable, propeller-less underwater robot better suited 
for military tasks such as sweeping mines and inspecting harbors-and 
for that they are hoping to mimic the action of the bluegill sunfish.

"If we could produce AUVs that can hover and turn and store energy 
and do all the things a fish does, they'll be much better than the 
remotely operated vehicles we have now," said James Tangorra, an MIT 
postdoctoral associate working on the project.

The researchers chose to copy the bluegill sunfish because of its 
distinctive swimming motion, which results in a constant forward 
thrust with no backward drag. In contrast, a human performing the 
breaststroke inevitably experiences drag during the recovery phase of 
the stroke.

Tangorra and others in the Bio-Instrumentation Systems Laboratory, 
led by Professor Ian Hunter of the Department of Mechanical 
Engineering, have broken down the fin movement of the bluegill 
sunfish into 19 components and analyzed which ones are critical to 
achieving the fish's powerful forward thrust.

"We don't want to replicate exactly what nature does," said Tangorra, 
who will soon be joining the faculty of Drexel University. "We want 
to figure out what parts are important for propulsion and copy those."

So far, the team has built several prototypes that successfully mimic 
the sunfish fin. They reported the successful testing of their most 
recent fin, which is made of a cutting-edge polymer that conducts 
electricity, in the June issue of the Bioinspiration & Biomimetics 
journal.

The latest fin is made of a thin, flexible material that conducts 
electricity. The fin is able to replicate two motions that the 
researchers identified as critical to the propulsion of the sunfish 
fin: the forward sweep of the fins and the simultaneous cupping of 
the upper and lower edges of the fin.

When an electric current is run across the base of the fin, it sweeps 
forward, just like a sunfish fin. By changing the direction of the 
electric current, the researchers can make the fin curl forward at 
the upper and lower edges, but it has been a challenge to make the 
fin sweep and curl at the same time. Strategically placing Mylar 
strips along the fins to restrict their movement to the desired 
direction has proven successful, but the team continues to seek 
alternative solutions.

Their first-generation fin successfully replicated the sweeping and 
cupping motions of the sunfish fin, but the motors that controlled 
the fin were too large and noisy for use in an AUV. The researchers' 
new approach, using the new conducting polymer, could eliminate the 
need for electric motors. The material can be assembled from a 
solution of chemicals, giving the designers more control over its 
molecular structure.

"This gives us the potential to build machines or robots in a manner 
closer to how nature creates things," said Tangorra.

In future research, the team plans to look at other aspects of the 
sunfish's movement, including interactions between different fins and 
between fins and the fish's body. That will help engineers figure out 
how to best adapt nature's principles to designing robotic vehicles, 
Tangorra said.

"To be appropriate for AUVs, you can't just look at these as 
propeller replacements," he said.

This research is funded by the Office of Naval Research.

--MIT--

Written by Anne Trafton, MIT News Office