Exoskeletons Ratchet Up Strength, Endurance

By Bettina H. Chavanne

The soldier exoskeleton has moved from the realm of science fiction to reality, with contractors like Raytheon and Lockheed Martin partnering with smaller firms to bring products to market. But one big challenge remains: convenient and safe power for these machines.

Helping troops lug the weight of their equipment around is serious business, and the U.S. Army is actively pursuing solutions.

“You can’t hump a rucksack at 11,000 ft. for 15 months and not have that have an impact on your body,” Gen. Pete Chiarelli, the Army’s vice chief of staff, told reporters in January. The Army and Marines are witnessing a rise in musculoskeletal injuries. “There’s no doubt our non-deployable rates are increasing.”

Heavier body armor and equipment, compounded by the challenging terrain faced by troops in Afghanistan, mean those numbers are going to grow.

For nearly a decade, a project launched by the Defense Advanced Research Projects Agency has been looking at ways to help with the heavy lifting. The Exoskeletons for Human Performance Augmentation, a program whose stated goal in 2000 was “to develop devices and machines that will increase the speed, strength and endurance of soldiers in combat environments,” is finally a reality. At the behest of the Army, a team at Raytheon Sarcos, led by Stephen Jacobsen, built an exoskeleton called XOS. Video of the device in action shows software engineer Rex Jameson in the metal suit running, jumping, even speed boxing a punching bag. Jameson also does a lengthy series of reps on a weight machine, pulling down 200 lb. (see photo). “He stopped because he got bored,” Jacobsen says, “not because he was tired.”

“Qualitatively the suit has good mobility,” says Jeff Schiffman of the Army’s Natick Soldier Research, Development and Engineering Center, who has worked on the project for several years. He says the XOS provides a roughly 10:1 gain for a human. “The idea is that if you’re holding a 200-lb. box, it’ll feel like 20 lb.,” he says. Schiffman and his team evaluate the suit for its biomechanical and physiological aspects. How comfortable will operating the XOS be for a soldier?

Human factors issues have been relatively easy to navigate, Schiffman says. The Natick team’s goal, he adds, is to combine all the processes so a soldier can easily operate and get in and out of the suit without help.

And then there’s the matter of powering the suit. The first suit Raytheon Sarcos built in 2002 was not powered. The XOS now is tethered to a hydraulic pump that gets its energy from an external power supply that can run on propane, hydrogen or gasoline (and in later iterations, diesel), says Jacobsen.

“Before you do it right, you have to do it at all,” he adds. He breaks down the power issue into several levels. “First you have to show you can do the biomechanics, that it can move like you move,” he says. Then you have to determine how large your actuators need to be to accomplish those movements, as well as how much power those basic movements (including step, squat, walk, run, stumble) will consume.

Jacobsen’s team built numerous backpacks powered by electricity and fuel, but to get the power they needed, they had to develop their own valve system, which he says was “as hard as anything we did.” The servo valves control the hydraulic fluid feed to the actuators. Jacobsen was forced to engineer the valves to meet the size, reliability and efficiency demands he sought for the suit.

Despite the meticulous engineering and effort the valve design required, Jacobsen is certain his system is the best way to power the exoskeleton. “[A hydraulic system provides] a high power and force-to-rate ratio. That’s why it’s used in machines with energetic requirements.”

He hopes to eventually use the suit itself as a power-generating system, to charge batteries as the user runs or while he sleeps. “We have the most versatility,” says Jacobsen. “We have the most power-to-weight and torque-to-weight [ratios]. We can drive it electrically with batteries or tether it to an internal combustion engine hydraulically. Every option is there.”

Jacobsen has done a study on different methods of generating power. One possibility is for the XOS wearer to have a case to carry around “like astronauts do,” intermittently setting it down during work and then relocating the powerpack as the person moves. A powerpack on the wearer’s back would be ideal. “He would be totally mobile during the time he had fuel,” Jacobsen says.

Although XOS is Army funded, it’s not the only game in town. Lockheed Martin has paired up with Berkeley Bionics on an untethered, hydraulic-powered exoskeleton called the HULC, or Human Universal Load Carrier. Berkeley Bionics has worked on strength-augmentation programs before, with products like ExoHiker and ExoClimber. But the HULC is for endurance augmentation—it decreases the “metabolic cost” to the wearer, the company says. Contained within its product information is the claim that the HULC decreased oxygen consumption of users walking at 2 mph. by about 5-12% when using the test unit without a payload. “When the users [carried] an 81-lb. approach load at 2 mph., [oxygen consumption] decreased by about 15% when using the prototype HULC,” the web site reports.

The HULC is not a full-body suit like the XOS. It is a “power-savvy technology that focuses on lower-extremity mobility,” says Doug Medcalf, business development manager for Lockheed Martin, which basically means it’s a pair of powered titanium legs. Users can squat, crawl and lift heavy objects. Medcalf, an Army veteran, says the HULC has applications beyond the military, including industrial and even medical assistance. The HULC “allows users to carry the weight they need [to carry], but without the wear and tear” on joints and muscles.

The hydraulic power comes from servos powered by lithium ion batteries. “By not having cables and power connections or a high power demand, we can keep [the system’s weight] to 53 lb.,” Medcalf says.

Aside from power-management issues, both HULC and XOS face environmental challenges. How do you protect sensitive sensors from the harsh operating environment of the battlefield? “The systems and servos are protected, but we’re always looking at ways to make them more durable in the most extreme environments,” Medcalf says.

Jacobsen says the first level of XOS prototype addressed human-factors issues, the second level of prototype dealt with power and usability in real-world situations and the third, or XOS 3 as he calls it, looks at how to shield the system from the environment and make it cost-effective to manufacture. There are entire parts of XOS 3 that are sealed away from dust and liquid, Jacobsen says. Mass production may also lead to molded aluminum or composite shells, obviating the need for tubes for the hydraulics.

XOS 2 is heading to Natick in October for human factors work, at which point XOS 3 will begin a full test run in Utah, where Raytheon Sarcos is headquartered.

The greatest challenge for the future warrior—covered in sensors beaming information to various mobile platforms, and leaping sand dunes in a single bound—isn’t the construction of a futuristic suit of armor, it’s powering all the energy-draining technology that comes with it.

Photo: Raytheon Sarcos

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