Jacqueline Conciatore

Desert dwellers and 'bots reveal physics of movement

NSF.gov | January 2nd, 2014 | Visit the original article online

Physicist Daniel Goldman and his fellow researchers at the Georgia Institute of Technology shed light on a relatively unexplored subject--how organisms such as sea turtles and lizards move on (or within) sand.

If you've ever struggled to walk with even a modicum of grace on a soft, sandy beach, you may appreciate the question. The answers that Goldman's CRAB lab (Complex Rheology and Biomechanics Laboratory) uncovers--with the help of living animals and biologically inspired robots--deepen our understanding not only of animal survival, evolution and ecology, but also, potentially, the evolution of complex life forms on Earth. The lab's research also assists the design and engineering of robots that must traverse unstable, uneven terrain--those used in search and rescue operations at disaster sites, for example.

Goldman first investigated the properties of sand, which can act like a solid, fluid or even a gas, when he was a doctoral student of physics at University of Texas at Austin. Later, as a postdoc in the University of California-Berkeley lab of biologist Robert J. Full (a leader in the field of nature-inspired robots), he helped investigate locomotion on complex terrain--cockroaches' climbing of vertical surfaces, for example, or spiders running over surfaces with few footholds. A fellow researcher, Wyatt Korrf, was interested in movement on a different kind of complex terrain--granular, shifting media. Goldman became hooked, and the two men started working together.

"Some of the insights and tools we developed then were incredibly helpful in my early and current research, in particular, air fluidized beds as a way to control ground properties," Goldman says.

To a student or lover of critters, Goldman's job might seem like a dream. He has worked with a large variety of desert dwellers and other animals, including geckos, zebra-tailed lizards, sidewinders , ghost crabs, sandfish, wind scorpions, funnel weaver spiders and hatchling loggerhead sea turtles.

In the lab and in the field, he and his colleagues observe these animals as they creep, crawl, walk, run, slither and otherwise transport themselves over or in granular matter. The researchers pin down precise details--the flexible spines on a spider's legs that appear to facilitate movement over a wire mesh, for example, or the way a snake flattens itself when climbing a slope. Then they design robots with the physical elements and movement patterns they want to know more about. With these tests as well as computer simulations and analyses, the team can develop, challenge and refine hypotheses related to physics principles inspired by the animals' movements.

The CRAB lab's cast of robot characters to date includes a robot modeled after baby sea turtles, as well as a sandfish robot.

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