Herr is trying to build a leg-powering machine that uses as little energy as possible—the first iteration draws a mere two watts, comparable to a portable radio—but can support 80 percent of an 80-pound load on a user's back. In its current design, because of the way it affects his gait, the wearer burns slightly more energy with the suit than if he were just walking with the load alone. But Herr thinks that within the near future, he can improve the mechanics so that the machine actually saves the wearer effort. Ultimately, he envisions weekend warriors using exoskeletons as recreational tools, strapping in so they can run through the mountains all day. While Herr muses about these kinds of self-powered systems as a long-term dream, Kazerooni implies to me that he's already part of the way there.
Kazerooni, another veteran of the Darpa program (neither he nor Herr has so far gotten additional money from the military beyond the original grant), says his Human Load Carrier (HULC) lower-body exoskeleton can operate for more than 20 hours without recharging. He says it allows the user to carry 100 pounds on his back and burn 15 percent less oxygen than if he was supporting the added weight alone.
Kazerooni's device wasn't ready for a public unveiling and, when pressed for details, would say only that the system is analogous to that of a hybrid car. Just as a hybrid uses the energy transferred during braking to recharge its battery, HULC capitalizes on the force transferred from the ground each time the user plants his weight on a different leg. The very act of walking keeps it juiced. He's now in the middle of a three-year, $2-million grant from the National Institute of Standards and Technology to modify his system so it can help people with mobility disorders. "This isn't just a war machine," he says. "Our machine could replace the wheelchair."
The closest competitor to the XOS is also a medical device, but on the other side of the Pacific, in Japan. Roboticist Yoshiyuki Sankai launched a company in 2004 called Cyberdyne (the same name as the firm that sparks the robot revolution in the Terminator films, incidentally) to market his full-body exoskeleton, now known as the Hybrid Assistive Limb, or HAL-5. Rather than using force sensors like the XOS, sensors in HAL-5 attached to the wearer's skin pick up signals from his muscles to determine how he wants to move. The suit's control system studies and then mimics a person's natural gait. This means it takes up to half an hour for the suit and the operator to get in sync—you can't just snap in and go. But since Cyberdyne sees the HAL-5 as both a rehabilitation device and nurse's assistant, the training period may not matter. Strapped into the battery-powered suit, a hospital worker could hoist heavy patients as if they were kids. Sankai is leasing the suit to customers now.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.