Methane explosions power these soft jumping robots

Posted by Thomas Anderson

Harvard researchers are currently devleoping "soft robots" that are capable of performing all sorts of functions robots made out of rigid materials, such as metal, are unable to do.

In the past, the researchers have managed to get the soft robots to stand, walk, wiggle under obstacles, and even change colors. Interestingly, engineers have now created a new soft robot with a different kind of skill, namely the ability to jump.

Yes, researchers are using small explosions produced by mixing methane and oxygen to make these flexible robots jump as far as a foot into the air. This ability to jump is important because it gives the robots a way to avoid obstacles, which is required if they are to become practical for use in the field in the future.

"Initially, our soft robot systems used pneumatic pressure to actuate," explained Professor Robert Shepherd.

"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."

The researchers created the three-legged jumping robot using a 3-D printer, which are made from a soft silicone material allowing the construct to flex and stretch. Tubes connect to the robot deliver an exact mix of methane and oxygen that is ignited using high-voltage wires embedded into each of the robots legs. That wire provides a spark that ignites the gases allowing the robots to jump into the air. The scientists also incorporated a simple valve into each of the robot's legs.

"We flow fuel and oxygen into the channels, and ignite it. The heat expands the gas, causing the flap to close, pressurizing the channel and causing it to actuate," Shepherd said.

"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."

When developing the jumping robotic systems, the scientists were concerned that the soft silicone material used in the robot construction might not be able to survive the small explosions.

"Nevertheless, it's a lot more powerful, but the question we had to answer was whether it was compatible - were the temperatures compatible - with this system," Shepherd noted.

"What we were able to show is, because the duration of the explosion is so short, the energies absorbed by the robot are small enough to be compatible with soft robots. What's more, the temperature of the robot increases by, on average, less than one kelvin."

Shepherd believes that the system could be used as a starting point to develop robots that are even able to run.

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