"
The key to performing well, regardless of the conditions of the sand, seemed to lie in how the turtles controlled their wrists.
"On hard ground, their wrists locked in place, and they pivoted about a fixed arm," Goldman said. "On soft sand, they put their flippers into the sand, and the wrist would bend as they moved forward. We decided to investigate this using a robot model."
These findings led to the development of FlipperBot, the first robot to employ flippers against malleable surfaces. The small droid is about 7.5 inches (19 centimeters) long, weighs 2 lbs. (970 grams), and has two motor-driven flippers with flexible wrists similar to sea turtle wrists
In experiments involving a bed of poppy seeds that simulated sand, the flexible wrist helped FlipperBot minimize slipping while moving forward. The flexible wrist also helped keep the robot's body angled away from the ground, minimizing drag from belly friction that could slow it down.
"It was surprising how sensitive this locomotion was to small changes in how the flippers move," Goldman said. "If you change things — even by a millimeter — it could be enough to make the thing move either well or poorly."
The robot and the turtles often did poorly when their limbs encountered sandy ground that had already been disturbed.
"If the ground the flippers go into was disturbed already, the flippers penetrate more deeply, and that causes the body to not lift as high and the belly to drag more," Goldman said. Successful flipper-based movement may depend on having flexible wrists that allow them to move without disturbing too much sand.
"Very small changes in gait or body structure can cause dramatic decreases in speed," Umbanhowar added.
These findings might help scientists better understand how turtle flippers work — which, in turn, could help build robots designed to both swim through water and walk on land.
"This work can provide fundamental information on what makes flippers good or bad," Goldman said.
In future studies, the robots could also help researchers understand how turtles, and other creatures with limbs designed for swimming, evolved to walk on land.
"We are now working with paleontologists on studying what the first animals moving on land were like with more paleontologically realistic robots," Goldman said. "These animals were not moving on concrete, on hard rock, but likely encountered materiallike sand and mud — which can flow and yield upon footsteps —and their limbs were likely flipperlike."
The robots could also help conserve endangered sea turtles.
"The natural beach habitat of hatchling sea turtles is endangered by human activity," Mazouchova said. "Robot modeling can provide us with a tool to test environmental characteristics of the beach and implement efforts for conservation."
Goldman, Mazouchova and Umbanhowar detailed their findings April 24 in the journal Bioinspiration & Biomimetics.