The off-road robo-roach
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Koditschek, working with Full, found that when a cockroach runs, its legs, though jointed, act like pogo-sticks. So, the team built their robot with six unjointed, C-shaped, flexible plastic rods for legs, which act as the machine’s shock absorbers. Each leg is powered by a motor, which spins the leg alongside the body like a one-spoked wheel. The legs hit the ground in the classic cockroach tripod gait and then swing over the shoulder to come down again. The resulting robot looks like a four-year-old’s drawing of a cockroach – a rectangle two-feet long with six sticks coming off it. Using a cockroach-inspired walk and suspension system, it runs stably over rocky ground, through vegetation, and can climb stairs.

Engineers at Stanford chose a design that takes the cockroach model a little more literally. Though the robot’s legs are, like the Michigan lab’s model, simple jointless pogo-sticks, its swinging stride and elastic hip joints mimic those of an actual cockroach.

Each of the robot’s legs is a pneumatic piston (a rod that moves within a nearly air-tight tube, like the motion damper on the top of many school and church doors), which, when filled with air, pushes its inner rod down and back, moving the robot forward. The legs themselves aren’t flexible, but a constant air pressure maintained in the hollow piston tube absorbs shocks and gives the legs their springiness.

The robot has another shock absorber in its hip, which Mark Cutkosky, the mechanical engineering professor who runs Stanford’s cockroach robot lab, and his team designed about four years ago. Roach hips contain resilin, the highly elastic material that launches fleas on their epic jumps, explains cockroach biologist Ritzmann.The resilin stretches during the backswing of the step and springs the leg forward again when the roach lifts its foot. Cutkosky’s team’s robot has a soft polyurethane hip joint that works the same way, automatically springing the legs back into stepping position after each tripod step.The hip-spring saves energy and is tuned to give the six-inch long robot, which can climb over obstacles as tall as its hip and run up to 2.5 body lengths per second, an extra degree of stabilizing suspension.