New Technique Helps Robots Walk Through Sand

Lee Rannals for — Your Universe Online

“Terradynamics” could be the next big thing in robotics, helping robots move on granular and other complex surfaces like beaches.

Studying the field of terradynamics involves researching and understanding how small-legged robots move on and interact with complex materials like sandy beaches. The team who coined the name terradynamics wrote about their achievements in the field in the journal Science.

“We now have the tools to understand the movement of legged vehicles over loose sand in the same way that scientists and engineers have had tools to understand aerodynamics and hydrodynamics,” said Daniel Goldman, a professor in the School of Physics at the Georgia Institute of Technology. “We are at the beginning of tools that will allow us to do the design and simulation of legged robots to not only predict their performance, but also to optimize designs and allow us to create new concepts.”

[ Watch the Video: Terradynamics Helps Robots Move Through Sand ]

Designers could use terradynamics to better develop robots like those designed to go on search-and-rescue missions. Currently, robots in this field rely on wheels for locomotion, but Goldman says new techniques need to be developed using terradynamics.

The researchers examined the motion of a small-legged robot as it moved on granular surfaces. They created a variety of shapes for legs using a 3D printer and studied how different configurations affected the robot’s speed along a track bed. They also measured granular force in experiments to predict forces on the legs.

Goldman said the key finding in their examinations was that the forces applied to independent elements of the robot legs could be summed together to provide a reasonably accurate measurement of the net force on a robot moving through granular media. This technique worked well for legs moving in diverse kinds of granular surfaces.

“We discovered that the force laws affecting this motion are generic in a diversity of granular media, including poppy seeds, glass beads and natural sand,” said Li, who is now a Miller postdoctoral fellow at the University of California at Berkeley. “Based on this generalization, we developed a practical procedure for non-specialists to easily apply terradynamics in their own studies using just a single force measurement made with simple equipment they can buy off the shelf, such as a penetrometer.”

The researchers also learned convex legs made in the shape of the letter “C” worked better than other variations.

“As long as the legs are convex, the robot generates large lift and small body drag, and thus can run fast,” Goldman said. “When the limb shape was changed to flat or concave, the performance dropped. This information is important for optimizing the energy efficiency of legged robots.”

Terradynamics worked well for more complicated granular materials, but future studies might need to look into the degree to which particles resemble a sphere. After more research, their technique could eventually provide designers with a better understanding of motion through media that flows around legs of terrestrial animals and robots.

“Using terradynamics, our simulation is not only as accurate as the established discrete element method (DEM) simulation, but also much more computationally efficient,” said Tingnan Zhang, who is a graduate student in Goldman’s laboratory. “For example, to simulate one second of robot locomotion on a granular bed of five million poppy seeds takes the DEM simulation a month using computers in our lab. Using terradynamics, the simulation takes only 10 seconds.”

Goldman said terradynamics opens up a new era, providing tools that help understand why lizards have feet and bodies of certain shapes.

“We think that the kind of approach we are taking allows us to ask questions about the physics of granular materials that no one has asked before,” Goldman added. “This may reveal new features of granular materials to help us create more comprehensive models and theories of motion. We are now beginning to get the rules of how vehicles move through these materials.”

In 2009, another group of researchers looked into finding out why robots get stuck in the sand. The team wrote in the journal Proceedings of the National Academy of Sciences about how they discovered that when a robot rotates its legs too fast or the sand is packed loosely enough, it transitions from rapid walking motion to a slower swimming motion.

Not only do these research projects pave the path for future “Baywatch” robots, but they also could help in further advancing our exploration of other planets.