Harvard Researchers Use Combustible Gases to Power Leaping Machines

Researchers are helping determine if robots can make some new moves, and that includes jumping.

With the help of small explosions produced by a mix of methane and oxygen, researchers at Harvard have designed a soft robot that can leap as high as a food in the air. The ability to jump could one day prove critical in allowing the robots to avoid obstacles during search and rescue operations, as described in a Feb. 6 paper in the international edition of Angewandte Chemie.

"Initially, our soft robot systems used pneumatic pressure to actuate," said Robert Shepherd, first author of the paper, former postdoctoral researcher in the Whitesides Research Group at Harvard, and now an assistant professor at Cornell. "While that system worked, it was rather slow - it took on the order of a second. Using combustion, however, allows us to actuate the robots very fast. We were able to measure the speed of the robot's jump at 4 meters per second."

Similar to other soft robots, the three-legged jumping system begins life as a mold and is then created by a 3-D printer. The robots are molded by using a soft silicone that allows them to stretch and flex.

However, as pneumatic robots are connected to tubing that pumps air, the jumping robots are lashed on to tubes that help deliver a delicate amount of methane and oxygen. With high-voltage wires embedded in each leg of the robot, researchers deliver a spark to ignite the gases, causing a small explosion that sends the robot into the air.

And among added design innovations, there is a combustion system to work, says Shepherd, which was the incorporation of a simple valve into each leg of the robot.

"We flow fuel and oxygen into the channels, and ignite it," Shepherd said. "The heat expands the gas, causing the flap to close, pressurizing the channel and causing it to actuate. As the gas cools, the flap opens and we push the exhaust out by flowing more gas in. So we don't need to use complex valve systems, all because we chose to mold a soft flap into the robot from the beginning."

While Shepherd said he hopes to see internal combustion systems developed that can allow robots to walk or even run, Shepherd said jumping made sense as a starting point.

"Because it releases so much energy so fast, it made sense for jumping to be the first 'gait' we explored with this system," he said. "The next step now is to learn how we can use this combustion system for other gaits, like running or even walking."