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o.nan"exo and even the weediest become unstoppable.Paul Marks discovers how to leap tall buildlngs at a singl~. bQ!~nd

IT has got to be the most outlandish militaryproject the Pentagon has ever dreamed up.In just four years, and with $50 million, theyplan to create a wearable, self-propelledrobotic suit that responds to-and ampli-fies-your every movement. Strap them-selves in and troops will be able to run faster,jump higher, leap further, and drape them-selves in awesome amounts of armour andhigh-calibre weaponry. It will turn youraverage GI into 11 heavyweight fightingmachine with superhuman powers-a kindof Tank Girl meets the Six-Million Dollar Man.

Despite the military slant, researchers onthe project say it's far more than simply toysfor the boys. They predict major civilianspin-offs for workers in construction,mining and heavy industries. Exoskeletons,the proper name for these mechanical suits,could help firefighters cut victims fromwrecked buildings or vehicles far fasterthan they can right now, and give disabledpeople new-found mobility-perhaps evenput a motorised spring in their step.

But if the machine isn't going to grindto a halt at the first drop of rain, or shootout of control like a runaway bulldozer,researchers need to develop a host of newtechnologies to satisfy their needs. They willhave to design a strong but figure-huggitlgframe of metal or composite materials withjoints that move in three dimensions. Trig-gered by motion sensors attached to armsand feet, small servomotors will allow the~ exoskeleton to respond to your every move~ (see Diagram, p 35). "This isn't a kit we're~ putting together," says Stephen]acobsen of

Sarcos, the Salt Lake City firm managingmuch of the project for the Pentagon'sDefense Advanced Research Projects Agency."We're like a baby in the forest on this, start-ing at the very beginning."

Which is why DARPA project managerEphrahim Garcia, an expert in smart mat-erials hailing from Vanderbilt University inTennessee, is casting his net wide. Garcia hasbeen kept very busy harnessing the skills ofa disparate bunch of US universities and high-tech companies to make the exo happen.

They face a rough ride. The history ofpowered exoskeletons is an unhappy one.The idea was first tried in New York state in1968, when the American electronics giantGeneral Electric in Schenectady, with aero-nautical engineers at Cornell University inIthaca, began developing a metal monster ofan exoskeleton called Hardiman. PictureSigourney Weaver's exoskeleton from Aliens,except with bridge girders, and you get theidea. GE got as far as demonstrating one armof the beast, which made lifting 700 kilo-grams feel like 20 kilos. "Hardiman was aninteresting system, way ahead of its time,"says Garcia. "But it was a massive machinethat would have required a small room loadof generators and hydraulic pumps to makeit function." It probably couldn't haveworked in the field autonomously.

In 1988, researchers at Los AlamosNational Laboratory in New Mexico designedwhat they dubbed a Powered Exoskeletal Suitfor the Infantryman, or PITMAN-inspiredby Robert Heinlein's 1959 sci-fi tale StarshipTroopers. But PITMAN remained on the

drawing board, crippled-like other earlyideas-by the lack of a power source to driveits joints.

Garcia and his bosses at the defencedepartment now believe that technology hasmoved on sufficiently to make the concepta reality. In particular, new lightweightcomposite materials and advances in micro-electromechanical engineering mean that it'snow possible to build small engines that arefar more fuel efficient than older designs."The time has come when we can fuel inject,or cpntrol the fuel burn, in microscopicquantities," says Garcia.

Initially, the developers at DARPA areaiming for an exoskeleton that lets troopsjog along effortlessly at 13 kilometres perhour carrying a 7a-kilogram load for 12hours at a stretch. Its superstrong frame-work, they believe, will support the weightof extra firepower and armour, plus theskeleton's own weight-another 20 kilo-grams

at least. That way, the theory runs,troops will conserve their own energy, and

boost their stayingcpower on the battlefield.But as researchers have discovered in the

past, the cornerstone of any exoskeleton isan efficient, light and reliable source ofpower.

Without that, there's no exo. "Thelong pole in the tent is definitely the energy

storage-that's the big question right now,"says Robert Martinage, an analyst at Wash-ington DC based think tank the Center forStrategic

and Budgetary Assessments.So what sort of power do you actuallyneed

to improve upon a person's walkingspeed and lifting power? " A human walking

10 November 2001. New Scientist. www.newscientist.com

33

'SHACKLE

YOUR BOOTSIN ANDY,OU CAN TROTAROUND

HAPPfLY TURNTHE POWER OFF ANDYOU FALL OVER'

working

on a "power piston" for theexo which captures the combustion energy

in a spring so it can be released slowly and

smoothly.Their system uses a spark to combust a

hydrocarbon fuel, driving a piston down achamber. By squeezing a hydraulic fluid, thepiston stores its energy in a powerful springheld in a neighbouring chamber. The idea isthat when required, the spring uncoils,transferring its energy back to the hydraulicfluid which, via a series of valves, providesseamless movement for the exo.

Roberto Pellizzari, until recently managerof the project at ADL, says that tests are dueto start soon on a prototype power pistonthe size of a cola can. Ultimately, the aim isto have the exoskeleton run on JP-S, themilitary's all-purpose fuel which can bum inanything from a camp stove to a jet fighter.

Garcia also has Quoin, a firm in Ridgecrest,California, exploring other approaches to pow-ering the exo. This company-which is alsodeveloping parts for the proposed US ballisticmissile defence system-not only plans togenerate exoskeleton motion with a novelminiature turbine, but also hopes to developan electricity supply for the copious electronicsensing, imaging and communicationssystems that a battle-ready suit would need.

Quoin's generator uses dual pistons that

about requires about 100 watts," says Garcia,"so we need hundreds of watts at the mini-mum, but probably 1 or 2 kilowatts."

That power requlrement-equivalent totrying to power one or two bars of an electricfire from a portable power pack-makesbatteries

a non-starter. You may be able todemonstrate an exoskeleton with batteries,says Garcia, but you'll never be able tobuild anything of any use. Researchers atSartos have calculated that an all-electricexoskeleton with batteries and motors wouldweigh an absurd 1800 kilograms.

Petrol powerAfter toying with a variety of fuels, Garcia'steam believe old-fashioned hydrocarbonswin hands down. Rather than using onelarge engine, the researchers think it mightbe better to dot small combustion enginesaround the exoskeleton. The problem will bepersuading these small motors to provideprecisely controlled amounts of power tomove the exoskeleton's limbs.

Garcia's researchers are pursuing onepromising idea-merging the fuel combus-tor and the limb actuator into one device.You might be able to do this with state-of-the-art microelectromechanical gadgets.Made from smart materials such as shapememory alloys, these tiny devices' can beused to throttle minuscule volumes of fuelinto a combustor, says Garcia.

To get a cross between a working powersource and an actuator, Garcia's high-techcontractors are racing each 9ther to come upwith the best design. In one variant,researchers at engineering company ArthurD. Little in Cambridge, Massachusetts, are

are connected to a reciprocating rod whichmoves back and forth. The rod is surroundedby a metal coil and as the rod moves, a smallmagnet on it induces an alternating currentin the coil. This could power sensors or otherelectronics mounted on the suit.

Beyond the motors and energy source, thenext problem is the pesky human body.Where, for example, do you put the actua-tors to best support the human gait? Andhow can you design the suit to be adjustablefor people of different heights and weights?

No one knows all the answers yet. ButBoston Dynamics, spin-off from MIT's LegLab, is trying to find the answers withpredictive modelling and computer visuali-sation. They're simulating combinedexoskeleton and human limb motion so thatwhen they build a prototype, the motorscan drive it in smooth, seamless motion.

Meanwhile, mechanical engineer WilliamDurfee and his team at the University ofMinnesota in Minneapolis are developingwhat's called the exo's IIsoft tissue inter-faces"-the bits that attach the person tothe machine. Unlike leg braces, for example,which attach via clamps or bone screws, theexo will have to be strapped or zipped on,with fittings that somehow minimise theloading on skin and muscle.

They're aiming for the coupling arrange-ment to be Illike a well-fitting shoe", saysDurfee. But as they move, wearers of thesystem will only feel it gently touchingthem, as it will be set up to II walk like you

walk, in synchrony", says]acobsen.Doing some of the legwork, quite literally,

is Homi Kazerooni. He's a veteran of manywalking robot projects at the Human Engi-neering Lab he runs at the University ofCalifornia at Berkeley.

Kazerooni's team became involvedbecause they've already built LEE-a lowerextremity enhancer. It's basically a pair ofpowered, wearable legs for an exoskeleton.Unfortunately, the lack of a decent powersource is all too obvious. LEE is driven by anoisy, heavy, exhaust-guffing chainsawengine the wearer totes around in a bulkybackpack. Shackle your boots into LEE's feetand you can trot around fairly happily-aslong as the engine is running. Switch thepower off and you just fall over.

Garcia expects a lot more than this crudetechnology for his $50 million. III want todistance the exoskeleton project from that[LEE] rig. It has a limited cyclical walkingmotion that doesn't sense your motion andtry to help you," he says. But it's early days,and the Berkeley team are confident theywill be able to create more complex legs thatsquat, bend, swing from side to side, twist,walk and run. At the same time, other

10 November 2001 .New Scientist. www.newscientist.com

researchers at Sarcos and at Oak RidgeNational Labs in Tennessee are developingthe suit's top half. And to support the weightof whatever weapon or rescue equipment thewearer is toting, the suit will need themechanical equivalent of hands-in thiscase, probably some kind of metal grippers.

With a complete exoskeleton frame andthe motors to drive it, the only thing youneed now ts the sensing system that lets youtell the exoskeleton when to lift an arm or

jump a ditch. This is going to come from anovel touch-based, "haptic" control systemthat will sense what the exo-wearer wants todo

and move accordingly.Each limb of the exoskeleton will beequipped

with an array of motion sensorsthat are in contact with the wearer's body.Once

they detect slight movement in an armor leg, for instance, the sensors will signal thehaptic

control system to switch on motorsthat move the exoskeleton's arm or leg to

match. This will have to be done seamlessly,without hindering any activity. These hap-tics will also have to feed back an authenticlifting sensation to the user so they don'tapply too much force and damage whateverthey're lifting-or the exoskeleton itself.

Simple haptic control systems are alreadyin place in the car manufacturing industry.On the production line, workers use hand-held controllers to manipulate items such aswindscreens with a robotic arm. Thesecontrollers even give the users somemechanical feedback-letting them knowhow much force they're applying to helpthem manoeuvre the objects into place. Buthow they're going to adapt such simplesystems for a much more complex exo-skeleton is unclear. And even if it were,DARPA has applied a minor league newsblackout on new exo developments. "W~ tendto get burnt if we promise too much inadvance," says DARPA spokesperson JanWalker. The researchers are optimistic,however. "This is the first time we've everhad a coordinated team effort," says Garcia.

They plan to have a prototype working byaround 2004. If it works as they hope, thesuit could eventually be capable of workingfor 18 hours and carrying a 140-kilogramload, says Jacobsen. "Exoskeletons couldhelp people out in all sorts of emergencyarenas," predicts Louis Piscitelle, a researcherat the US Army's Soldier Systems Center inNatick, Massachusetts. In a nuclear accident,for example, an exoskeleton could carry ahuge weight of lead shielding, giving theengineer who dons it more time to tackledangerous spills without exposing them-selves to a fatal dose of radiation. It couldeven be given a degree of autonomy-so thatshould its wearer be injured, the suit couldsimply stroll to the nearest first aid post.

Yet the machines themselves aren't risk-free. Heading into a burning building or ontoa battlefield strapped inside an exoskeletonloaded with highly flammable fuel is goingto take some guts. "If the fuel is alcohol-based, it will easily bum," says KeijiroYamamoto of Kanagawa University in Japan,who is developing a compressed-air poweredexoskeleton (New Scientist, 28 July,p 22). Andsince you'll be locked into the suit, majormalfunctions could easily be fatal. In factGE's Hardiman was never turned on "for fearof what it might have done to the poor guyinside", says Garcia.

Climbing into one of these meanmachines is sure to convert you from a wimpto an invincible giant. But just remember:stay away from naked flames, weak bridgesand large magnets. And if your nose beginsto itch, whatever you do, don't scratch it.You may never see it again. D

10 November 2001 .New Scientist. www.newscientist.com 35