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Square tails grip better: researchers discover advantages in the seahorse tail that could be applied to robots.

Seahorses don't gallop through the oceans. They are, in fact, the slowest swimming fish in the world. Instead, seahorses spend their days holding onto sea grasses and other objects with tong, plated tails, waiting for tasty crustaceans to float by.

Those tails are made of 36 segments, each squarish in cross-section, which is odd for the animal world. "Almost all animal tails have circular or oval cross-sections--but not the seahorse's," said Michael Porter, an assistant professor of mechanical engineering at Clemson University in South Carolina. "We wondered why."

Porter and colleagues at the University of California, San Diego, Oregon State University in Corvallis, and Ghent University in Belgium believe they have found the answer. They have demonstrated that not only do square tails grasp better than round ones, but the square plates make the seahorse tail stiffer, stronger, and more resistant to strain.

To better study how the seahorse tail works, Porter and his team designed and built two artificial exoskeletal tails--one made up of four, overlapping L-shaped plates like a seahorse tail, and a similar one made with quarter-circles instead of right angles. The plates were 3-D printed and held together with springs and elastic bands.

When the engineers ran the two model tails through their paces, the limits of the round one became quickly apparent. The round tail twisted easily, but it required some effort to straighten it out. By contrast, although the square tail didn't twist as much, it more readily returned to its original shape.

What's more, while both square and round tails could bend with the same radius of curvature, the square tail provided more points of contact. The square tail may provide the seahorse a better grip on underwater objects. (Many animals--like monkeys--have prehensile tails with round cross-sections, but they are covered in flesh or fur, which deform to grip objects.!

The square tail also performs as armor. Under crushing pressure--as if a predator was taking a bite--plates of the round tail splayed outward at the sides, while L-shaped plates simply slid next to one another. In lab tests, the square cross-section 3-D printed tail supported a compressive load three times greater than the round one.

The insights into the seahorse's tail may be applicable to robots. Researchers are looking at building robots from soft, deformable parts, but squishy machines are prone to damage. Covering moving parts in armor designed to deform and protect could enable robotic tendrils to snake along and grab objects, or to work their way through rubble. Porter also is interested in developing a steerable catheter, but that's an application where using square corners may be unwise, no matter how strong or flexible they are.

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Title Annotation:TECH BUZZ
Publication:Mechanical Engineering-CIME
Geographic Code:1USA
Date:Sep 1, 2015
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