Wall-scaling tank-bot inspired by geckos

A tank-like robot that uses a gecko-inspired strategy to scale smooth surfaces like glass has been developed by a group of B.C. researchers.

A tank-like robot that uses a gecko-inspired material to scale smooth surfaces like glass has been developed by a group of B.C. researchers.

Jeff Krahn, a research assistant in the engineering science department at Simon Fraser University in Burnaby, B.C. and his colleagues, demonstrated their new robot rolling up a whiteboard in a video posted on YouTube. The segmented robot has two tank-like treads at the back and two in the front, separated by a motorized joint. The design allows the robot to bend around a corner as it moves from a horizontal plexiglass surface and starts heading down a vertical one in the video.

The robot itself may not look much like a gecko, a small lizard famous for its sticky feet and its ability to run up and down slippery walls or even across the ceiling. But at a microscopic level, the tank treads are made of a material designed to imitate the stickiness of a gecko's feet.

The researchers suggest similar robots could make their way across slippery surfaces to scale normally inaccessible sites, so they could be used to inspect pipes and parts of buildings or airplanes, or be used in search and rescue operations.

The prototype was described in an article published this week in the journal Smart Materials and Structures.

A Tokay gecko clings upside-down to the glass of an enclosure at a reptile park in Singapore. Geckos are famous for their ability to climb smooth surfaces, thanks to the design of special hairs on their feet. (STR New/Reuters)
A gecko's feet have pads covered in small hairs made of a material that can interact with many surfaces using Van der Waals forces, a weak attraction that forms between molecules when they temporarily develop opposite charges where they contact one another.

That allows them to do what magnets, suction cups or claws have trouble with – stick to and climb smooth surfaces such as glass or plastic.

The treads on Krahn's tank-bot uses a material called polydimethylsiloxane, which can make use of Van der Waals forces and has other qualities that make it practical for robot-building.

"It's very liquid, so it can easily fill the forms of our molds," Krahn said in an interview Wednesday.

"It's easily cleaned and long-lasting. And, of course, it seems to have good adhesion compared to other materials."

The hairs on a gecko's feet are branched, allowing them to make better contact with uneven surfaces.

"They're kind of like the fibres that we created," Krahn said.

The "fibres" on the tank treads are a flat-topped mushroom shape that were easier to fashion using a mold, and have been found to make good contact with uneven surfaces made of smooth materials such as glass.

Krahn chose to put the material on tank treads that automatically attach to a surface and then peel off again at an angle as they move around a belt, because this approach to locomotion is far simpler than controlling four legs and feet. And peeling a foot away from a surface is a particular problem, he said – pulling it directly away isn't very effective due to the strength of the "sticking" forces, so a legged robot would need to employ a special peeling motion to make that easier.

Researchers at Stanford University developed a gecko-like robot called "Stickybot" in 2010 that climbed on four "feet." However, Krahn's robot is a simpler machine that can achieve the same goal — climbing smooth, vertical surfaces to reach sites that are normally hard to access.

He was partly inspired by other tank-like climbing robots that have been built. Those relied on an actual wet glue to stick to surfaces rather than a dry, gecko-inspired material. They also had a rigid tail to help apply more pressure to the front treads and keep them from peeling off.

However, the tail would get in the way as the robot moved from the floor to a wall, so Krahn used a different strategy to keep the front of the robot from peeling away from a surface. When the robot detects that the front treads are losing contact, the motors on the joint rotate to apply more force at the front.

Krahn, who hopes to start his Ph.D. in January, would like to improve the design of both the tread material and the robot itself. He said his colleagues are working on a "spider-like" gecko-inspired robot.