Big, blue and full of air, the AntRoach blow-up

Big, blue and full of air, the AntRoach blow-up robot is both light on its feet and as strong as an ox – Sara Reardon saddles up

I'VE ridden horseback before, but nothing could prepare me for riding a 5-metre-long balloon through a dusty pipe-organ factory. My mount, named AntRoach for its anteater-like nose and six legs, lurches from side to side as engineers use a laptop to navigate the semi-autonomous inflatable robot across the wood floor. Each step is accompanied by the loud exhaust of pressurised air from its joints, as I cling nervously to AntRoach's polyester sides.

"You comfortable there?" asks Peter Lynn, who describes himself as the "chief seamstress officer" at Otherlab, a start-up in San Francisco's Mission district that manufactures inflatable robots along with hydraulic controls for solar-power systems and the odd electric vehicle. I nod, all too aware of the designers and engineers watching, amused, as the blue creature lumbers through the doorway and past an antique coffee bar where they lounge.

I am the first reporter to ride AntRoach: Otherlab's demonstration of a pneumatic control system that rapidly pumps air in and out of small compartments sewn into the robot's joints to make it walk - and swivel its proboscis. The system, modelled on a squid's musculature, inflates the compartments to around four times atmospheric pressure, causing them to push off one another and generate movement.

Engineered correctly, an inflatable robot could move as fast as a car's airbag inflates, Otherlab founder Saul Griffith says. AntRoach isn't there yet - it can reach about 8 kilometres per hour. But the prototype is very strong, I'm relieved to hear. Despite weighing only 35 kilograms when deflated, it can carry up to 450 kg.

Besides having a high strength-to-weight ratio, inflatable robots should have the edge over more conventional ones in agility, because they can quickly inflate and deflate the small chambers that act as pneumatic "gears". Griffith has his sights set on BigDog - the rugged pack-mule-like robot built by Boston Dynamics - as the one to beat. With the right control system and software, he says, an inflatable robot could "beat BigDog in a cage fight - if BigDog isn't allowed to carry a knife".

Poppability notwithstanding, softer robots have other advantages. They would be less painful to bump into around the house than a metal robot, for one thing. With few mechanical parts, and given the right kind of stitching, they should also be relatively quick to manufacture. That will make them affordable as test beds for new software for artificial intelligence or control systems, Griffith says. They are cheap to power, too: a canister of compressed air could power an inflatable robot for as long as a battery no bigger than the canister itself. Best of all, they can be folded up and carried around in a backpack.

Although unlikely to replace traditional robots entirely, inflatable devices could have the upper hand in tasks that require a soft touch, like lifting a hospital patient out of bed or evacuating wounded soldiers from the battlefield. The possibility has interested the US military's Defense Advanced Research Projects Agency enough for it to offer partial funding for Otherlab's work.

I experience some of that potential when, at Lynn's behest, I stick my head into the claw-like appendage of Otherlab's newest robot, which is modelled on an elephant's trunk. The pressure on my temples feels immense, though so far it can only lift about 5 kg. Much more friendly is their "human" arm robot with fully movable fingers, which shakes my hand with a grip that is firm yet gentle. Lynn says both robots could be 10 times stronger if built out of Kevlar or another material that can withstand higher pressures.

Elastic robots pass the eggshell test

At the Massachusetts Institute of Technology, George Whitesides is developing both pneumatic robots and starfish-like automatons made of elastic materials that stretch and slide through tight spaces. Their niche, he says, will be in tasks such as surgery and search and rescue - "anything where you don't want a set of grippers ripping into you," he says.

His team has tested their elastic gripper by having it pick up an uncooked egg. Even the most precise metal grippers would struggle not to crack the shell, but soft robots avoid this as they simply mould themselves to an object's shape. Such robots "will find new tasks to do" that their metal and plastic counterparts cannot manage, Whitesides says.

Issue 2873 of New Scientist magazine