Machine Design


Body amplifiers are getting closer to reality.

Edited by Stephen J. Mraz

A software engineer straps himself into a metal suit suspended from above. When the man wearing the exoskeleton moves, the machine mimics his every motion. As he throws jabs and bounces from foot to foot, so too does the suit, like a boxer. Considering this high-tech suit weighs 150 lb, he’s light on his feet. Then, he snatches a 200-lb bar and snaps off 50 nearly effortless pulldowns. He’s been known to do 500 before boredom sets in.

Steve Jacobsen and a team of engineers at Sarcos — the Salt Lake City robotics company he started in 1983 which was recently purchased by defense giant Raytheon — developed the XOS (exoskeleton) with funding from the Pentagon’s Defense Advanced Research Projects Agency (Darpa). But Jacobsen sees applications in construction and the medical field as well. (Imagine an orderly whose strength was amped up by, say, a factor of 10.)

The team is on the cusp of realizing the military’s decades-old vision of mechanically enhanced soldiers capable of carrying heavy loads. Using artificial muscles and controls, these powerful suits could soon be available to soldiers, firemen, even the handicapped. The biggest problem is in finding a portable lightweight power source. But Jacobsen claims that’s only six to nine months from being solved.

For reasons of power-to-weight ratio, the company looked at many systems but settled on hydraulics which have peak pressures of 3,000 psi. The actuators are rotary type. So far, hydraulics have been powered by electric motors in the 1 to 3-hp range or by an internal-combustion engine. “But now that we have [power] consumption down, we’re going to use two power packs, one electric, the other fuel powered,” he says. It takes about 1.5 hp to walk 3 mph, but XOS has moved as fast as 6.2 mph.

Wearers can climb a 30% grade and walk on their heels, if necessary. Depending on the intended use, future suits could be bulkier or more slimmed down. For every pound of load the wearer assumes, the suit assumes 10.

“For Darpa, we had to make something that was agile, quick, and strong. We’ve been making articulated robots for 20 years and are probably the best people to develop the XOS,” says Jacobsen. The device lets wearers raise 150 lb over their heads 130 times and lift about 250 lb at one time. “It magnifies what wearers do by whatever gain we pick.”

But isn’t this contraption heavy by itself? Not really. When the wearer raises an arm, the resistance is about 1 lb. A slightly built woman from Darpa lifted 35 lb at arm’s length using only her thumb.

Now the company focuses on more sophisticated versions that could be mass produced. Raytheon, Waltham, Mass., will manufacture exoskeletons and Sarcos, a selfdescribed skunkworks, will keep developing. “Many who worked on the project are hobbyists or are obsessed with the concept. We pick people who know a lot of things, like electronics, mechanics, and software,” says Jacobsen.

Could an exoskeleton-wearing soldier march for 8 hr carrying a 200-lb pack? “I’ll bet he’d be a heck of a lot less tired using it than not using it,” says Jacobsen. “But our real goal is to take the person out of the exoskeleton, put the circuits in, and build the best humanoid (robot) imaginable. We could put longer arms on it and make it a quadruped. Or we could make it a hexapod with six legs.” Jacobsen claims his company has solved the problem of robotic legs lacking speed, grace, and strength.

Exoskeletons would let the military reduce exposure of its troops, for example, by having one soldier in the field doing the work of three. Another goal is to get the cost of an exoskeleton below that of a small automobile.

That said, an exoskeleton takes some getting used to. “One of the people who tried it said: ‘You can cancel the weight but not the mass.’ But if you develop a knack for it, you can just walk away,” says Jacobsen. “Some U.S. Army colonels came and tried it out. Then they shook hands and left. They just wanted to know if it was real.”

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Copyright 2007 SILC


The exoskeleton has military uses, most importantly reducing the number of soldiers in harm’s way. It could also be used in hospitals and other car facilities to move patients or to give mobility to people with disabilities.

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