Researchers are edging closer to fielding a gas-powered system that will permit
soldiers to effortlessly carry hundreds of pounds of equipment on the battlefield.
The program, sponsored by the Defense Advanced Research Projects Agency (DARPA),
is paving the way for robotically enhanced soldiers, but not necessarily futuristic
front-line warriors, caution scientists.
Contractors and the program manager of the exoskeletons for human performance
augmentation (EHPA) said that, while the option for battle-ready, wearable robotic
suits remains open, the system that is being currently pursued is aimed at allowing
soldiers to tote enormous loads.
“This thing is useful for carrying payload,” said DARPA project
manager John Main. “It could be 200 pounds of food, or it could be 200
pounds of body armor.”
The overall goal of EHPA is to develop devices that increase the speed, strength
and endurance of soldiers in combat environments. When EHPA was launched in
2000, visions of massive power suits that propelled wearers over buildings and
through walls—mainly products of the fertile imagination of science fiction
writer Robert Heinlein—leapt into people’s minds. The reality may
be more mundane, but the challenge remains enormous.
“This is a fairly boring transportation program,” Main said, with
a small grin. “We’re not jumping over buildings. We’re getting
into rough terrain that is denied to Humvees.”
In 2001, six contractors were left to pursue the development of self-powered,
controlled, and wearable strength augmentation systems. The first challenge
was proving that actuators—machine muscle—and high-density, man-portable
energy sources were feasible.
In the fall of 2003, two contractors—the University of California-Berkeley
and Sarcos Research Corp.—were chosen to create the system. Locust USA
Inc. of Miami and TIAX LLC, of Cambridge, Mass., are working on the power source.
The words off-the-shelf are not used much in the exoskeleton program, Main
said, since everything is being built and optimized specifically for the product.
“Every part going into the exoskeleton needs to be designed from the ground
up,” he said.
It may be too early to plan around real-world applications, but military personnel
are watching the development of the project. Those who handle logistics envision
exoskeletons loading trucks, while infantry commanders see the extra weight
dedicated to shielding, Main noted.
“If you think about this in terms of airplanes, we’re about at
a Wright flier,” Main said. “Three years ago no one thought it would
Two teams of researchers late last year proved that the idea behind EHPA was
technically possible. Last August, a research team at University of California-Berkeley’s
robotics engineering lab operated their Berkeley lower extremity exoskeleton
(BLEXX) from a tether. The prototype weighs 90 pounds and allows a soldier to
carry 80 extra pounds without feeling it. Sarcos soon followed with an untethered
prototype that could handle 125 pounds.
The two projects are approaching the systems problems in different ways. At
Sarcos, sensors in the foot respond to force and apply a counter-force that
nullifies it and quickly tells actuators in the joints to bear the load. That
way the EHPA wearer does not feel the greater weight, and does not have to think
about operating the system.
The exoskeleton system at Berkeley responds to what the body is doing and adjusts
its behavior accordingly. For example, the leg acts differently while the foot
is raised in mid-air as opposed to on the ground. Fast computer processing matches
the machine with the human body’s changing states.
The head of the Berkeley effort, Homi Kazerooni, told National Defense his
team is leaving the future uses for military engineers. For him the true challenge
is to seamlessly integrate and synchronize the movements of man and machine,
not to create a man-shaped battle tank. “We are not thinking of the exoskeleton
as a suit of armor,” he said. “We’re looking at the exoskeleton
as a mobile platform, good for carrying mission-critical systems. This is a
lot different than the movies, or what science fiction authors write about.”
The key is to make a robotic system that can keep up with split-second demands
of human operators. With positive-definite points of contact at the feet, back
and shoulders, coupled with other compliant sensors at the hip or leg, the system
relies on the scores of linked nodes, placed close to sensors and actuators,
to bond the system in a moveable local area network. The nodes are arranged
in rings—one for each leg, and an additional ring for any mission-critical
electronics gear unrelated to the exoskeleton.
“Agility is a function of the computer and the hardware itself,”
Kazerooni summed up. The goal, he added, is to create a machine that’s
“transparent,” one that a wearer can use without feeling it, as
with a garment.
“Exoskeletons have the number one most difficult problems in robotics,”
said Kazerooni. “We’re taking on those problems on a systematic
Power supply is as important to exoskeleton systems as design, Main said. “During
the last three or four years, we’ve winnowed down to three engines,”
he said. “They have to last a minimum of 1,000 hours…The challenge
you have is to make a power system that does what muscles does: convert fuel
directly into work.”
Given the parameters of military missions, there is a premium on conserving
power. Actuators that mimic muscle cannot waste fuel while idling, but also
must be ready for action in microseconds.
Kazerooni conceded that robotic enhancements worthy of combat were feasible,
given a system design that could keep up with soldiers’ reflexes. “Can
the machine shadow our reflexes? These are not voluntary, and sometimes 200
microseconds is not fast enough.”
Kazerooni said that upper body enhancements, focused on arm strength and automated
gripping, are better suited for logistical support rather than combat since
soldiers want their hands free. “We don’t know what to do with upper
body extremities except logistics,” Kazerooni said. “Soldiers never
want to lose the weapons from their hands.”
For prototype testing, DARPA turns to the ergonomics experts at the Army’s
Natick Soldier Center in Massachusetts. By bringing the human factor into the
development of the EHPA system, designers hope to circumvent design problems
early and ensure that the system is as transparent as hoped.
“What better time is there than when you’re building the equipment?”
said Jack Obusek, team leader for the ergonomics team at Natick. “We can
make quantifiable measurements in movement patterns and changes in the force
on the body of the wearer.” Unpowered prototypes from Sarcos and Berkeley
already have been tested at Natick, and powered tests are scheduled for early
next year. While there, lab scientists will don the leg gear and perform a series
of incremental tests as Natick personnel collect data on the changes in force
patterns on the wearers and examine any biomechanical shifts induced by the
He said that the next round of tests would be very lab-based, but that the
future could hold involve obstacle courses and harsh terrain.
Still, no one understands the challenges of making a combat-ready robotic enhancement
system like a PhD. in biomechanics, and Obusek said he doubts the exoskeleton
system will be used to knock down walls or pound down doors in urban combat
since any force exerted must be matched in the opposite direction—the
soldier in the suit. “You’ve got to remember the laws of physics,”
Still, he said EHPA could provide the framework for improved ballistic armor
or medical evacuation equipment, applications that could find a home in a combat
The fuel issues are equally unique to EHPA. The concept of the internal combustion
engine is being reworked by researchers to be more compact, efficient and quiet.
“Efficiency gets you power density,” said John Bowman, senior manager
in charge of the exoskeleton program for TIAX. “Technology is pushing
things to much higher efficiencies from small-scale engines.”
The system features a two-stroke, linear-free piston engine that drives hydraulic
fluids at high pressures. The final product will have a six-inch diameter and
is 12 inches long, and meets another key EHPA requirement by running quietly.
Bowman declined to discuss how his team keeps engine noise to a minimum. As
far as fuel, prototypes run on propane but his team is advancing into gaseous
fuels that are “more appropriate to the military,” Bowman said.