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Soft Bots Jump With the Boom


by Charles Q. Choi

Engineers looking to make soft, rubbery droids that could be useful in future search-and-rescue operations more mobile are researching tiny explosions to propel them as much as a foot in the air.

If successful, future soft bots may contain internal combustion engines to drive them on missions, such as squirming through rubble to find trapped disaster victims.

Conventional robots are made of rigid parts, making them vulnerable to damage from bumps, scrapes, falls and twists, which could make it impossible to wriggle past obstacles. Inspired by creatures such as octopuses, worms and starfish that thrive despite lacking hard skeletons, researchers have recently devised flexible robots from soft, elastic plastic and rubber that can squeeze under obstacles, lift up to 120 times their own weight and change colors to hide in or stand out from their surroundings.

Soft robots are typically controlled by driving bursts of compressed air in and out of a series of pneumatic channels running through each of their limbs. However, these systems are rather slow, taking on the order of seconds to work.

"We were working with pneumatically powered soft robots and doing a lot of interesting stuff with them — grippers, mobile robots that can navigate obstacles — but the time to actuate them was taking a little long," says Cornell University researcher Robert Shepherd.

Now, Shepherd says, explosions could help those soft robots move very quickly. “We can now use combustion as a power source in soft robots,” he says.

The team made their three-legged prototype robots from silicone rubber that could bend and flex. The molds for these devices were created simply, cheaply and quickly using 3-D printers. These machines work by depositing layers of material much like ordinary printers — many print with hot plastic–building layers vertically that automatically fuse with the one below.

While conventional soft robots are connected to tubes that pump air, these new soft robots are connected to tubes that can deliver combinations of methane and oxygen at concentrations designed to minimize the formation of soot that could clog valves. Next, high-voltage wires embedded in each of the robot legs can deliver sparks to ignite the gases. The hot, expanding gases then pressurize the legs. As the gas cools, flaps open that allow the exhaust from the explosions to escape when more gas flows in.

The explosions cause the droids to leap at speeds of up to roughly eight miles per hour. In contrast, pneumatic robots only walk at speeds of roughly 350 feet per hour. Combustion happens quickly, so the robot’s temperature rises by less than one degree Celsius on average, easily allowing the droids to survive.

One weakness of pneumatic soft robots is how difficult it seems to power them in the field — they would either need to drag tubes behind them to remain connected to an air supply, or lug around canisters of compressed air. The Cornell team’s new findings suggest that combustion engines could provide the power for soft robots to walk, run or jump free from tethers.

The researchers note they could improve these robots further by using more potent fuels and stronger and lighter soft materials. Better control of the sparks could also help improve the energy efficiency of combustion and direct the jumps of the robots.

Shepherd, along with George Whitesides at Harvard University and their colleagues, detailed their findings online Feb. 4 in the journal Angewandte Chemie.

Top Image: Screen capture from Youtube video. Courtesy Harvard.

imageCharles Q. Choi
 has written for Scientific American, The New York Times, Wired, Science and Nature, among others. In his spare time, he has traveled to all seven continents, including scaling the side of an iceberg in Antarctica, investigating mummies from Siberia, snorkeling in the Galapagos, climbing Mt. Kilimanjaro, camping in the Outback, avoiding thieves near Shaolin Temple and hunting for mammoth DNA in Yukon.

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