Sticky tank climbs the walls

By Hamish Johnston

A major breakthrough in gecko physics occurred in 2002 when Kellar Autumn and colleagues at Lewis and Clark College in Oregon showed that the lizards use Van der Waals forces to stick to (and scurry up) smooth vertical walls.

Since then, researchers have worked hard to mimic the structures found on gecko feet. Indeed, Stanford University’s Sangbae Kim has already built a “Stickybot” robotic lizard that is capable of climbing walls. Stickybot solved an important problem facing a gecko-inspired climber – how to make a foot that sticks when you want it to, yet releases when the climber takes a step upwards. Kim’s solution is “directional adhesion”, whereby the stickiness of a foot depends on the directions of the forces applied to it.

Another approach to the stick/release problem involves using continuous treads of an adhesive material that resemble those you would find on an army tank or bulldozer. The main problem with such “tank” climbers is that a tail is needed to ensure that there is an inward force at the front of the tread so that it grabs onto the wall.

Now, Jeff Krahn and colleagues at Simon Fraser University in Canada have invented a tank robot that doesn’t need a tail – something that greatly simplifies the robot’s design. You can see the robot in action in the video above.

Another feature of the robot, according to the researchers, is that it is the first tank robot to use treads with microstructures that mimic gecko feet (right). Previous climbing tanks had used flat, unstructured materials.

Krahn’s robot, however, has treads covered in tiny mushroom-like structures that protrude slightly from the surface. The caps of the mushrooms are about 10 µm in diameter, with the stalks being about half that size. According to Krahn, this overhang allows the treads to grab on to rough surfaces.

The robot is described in a paper published in Smart Materials and Structures.