Video: Sand swimming robot

Just like a sandfish (Image: Yang Ding and Dan Goldman)

TO ADD to the robots that can crawl over land, fly through air and swim underwater comes one that can swim through sand. Such robots could help find people trapped in the loose debris resulting from an earthquake.

Navigating through sand is harder than moving through water or air because sand can behave as both a solid and a fluid. We have no equations to describe how such substances flow, let alone to predict how an object can “swim” efficiently through them.

But the sandfish lizard, Scincus scincus, can travel through sand effortlessly, so Daniel Goldman and Ryan Maladen’s team at the Georgia Institute of Technology in Atlanta decided to find out how they do it. They found that once the sandfish is submerged, it tucks its limbs into its sides and propels itself forward by wiggling from side to side.


Working with Paul Umbanhowar of Northwestern University in Evanston, Illinois, the team plugged their results into a computer model, which they used to show that a snake-like robot with just seven body segments could travel through a granular medium like sand.

Encouraged, the team built a 35-centimetre-long version of the robot, made from seven aluminium segments linked by six motors, all clothed in spandex to prevent the motors from becoming jammed.

The team then tested their robot by burying it in a container filled with plastic spheres 6 millimetres across. When the robot undulated its body at a frequency similar to the lizard, they found it could move forward at speeds of up to 0.3 body lengths per wave cycle – just below the 0.4 body lengths per cycle that a submerged lizard can achieve.

The robot could eventually match the lizard for speed, says Goldman, if more jointed segments are added to make its movements smoother.

Howie Choset, a roboticist at Carnegie Mellon University in Pittsburgh, Pennsylvania, thinks that the physics and the biology-inspired approaches to robot movement will one day meet and “at the intersection will be a deeper understanding of how biology works and how to make robots better”. The team will present their robot at the 2010 Robotics: Science and Systems Conference in Zaragoza, Spain, next week.