Hopping robot powered by explosions

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CHICAGO­ —Tiny explosions may be the next big leap for jumping robots.

Igniting a mix of oxygen and liquid butane releases a burst of energy that can propel a new soft-bodied robot skyward. Inflating the bot’s rubbery legs before the explosion can control which way it hops, researchers from Harvard and Cornell reported September 15 at the IEEE/RSJ International Conference on Intelligent Robots and Systems.

The robot has potential for use in disaster zones, said MIT engineer Sampriti Bhattacharyya, where rubble littering the ground can make it difficult for rescue robots to walk. “You want something very fast that can climb over broken stuff.”

Unlike traditional search-and-rescue robots, with rigid metal or plastic parts, robots with soft bodies can be resilient to damage and may pose less physical threat to humans. But making squishy bots hustle is a challenge, said study coauthor Michael Tolley, a Harvard mechanical engineer.

He and colleagues recently built an untethered soft robot that could survive fire, snow and even being run over by a car. But the silicone-based machine crawled along the ground about as fast as a garden snail.

Large leaps would make for faster travel, but “jumping is quite difficult,” said Mathieu Babel, an engineer at Parrot, a Paris-based electronics company. “You need to release a lot of energy in a very short amount of time. That’s why combustion is a good way to do it.”

In a project partially funded by DARPA, Tolley and his team built a pie-sized bot with a tripod of silicone legs that each look something like a Slinky dipped in melted erasers. The three legs extend from a central chamber that holds the robot’s brains and guts. A fourth, springlike limb protrudes down from the chamber’s middle.

To position the robot, a program cues a built-in air compressor to pump up the legs, which inflate like balloons and tilt the body in the direction of the jump. Then, the bot releases oxygen and a bit of butane into the springlike limb from a canister stashed inside the body.

The gas and fuel mix and an electrical spark triggers an explosion that forces the springlike limb to shove off the ground, rocketing the bot into the air. In about a second, such a launch can fling the bot as far and high as 0.6 meters, about the height of two 2-liter soda bottles stacked on top of one another.

Tolley’s team got the bot to jump onto a chair-high box and slide to the ground on the other side. But before the robot is ready to bound over rubble, researchers need to figure out how to stick the landing. The bot often lands on its head, Tolley said. “We’re working on that.” To make successive jumps, he said, “you can either land on your feet every time, or you can flip yourself when you land.”