PowerWalk device converts soldiers' movement into energy

Army officials say they are closing in on their goal of developing a means for soldiers on foot to recharge their many electronic devices simply by walking.

A technology presently in development, the “PowerWalk” device would harvest energy produced through the motion of walking, storing up juice in a battery which in turn could recharge phones, GPS, ranging and targeting devices, and a variety of other gadgets.

“Every time we give the soldier a new capability, it requires more batteries. Right now soldiers are carrying anywhere from 16 to 20 pounds of batteries just to maintain their mission posture,” said Noel Soto, a project engineer at the Army Natick Soldier Research, Development and Engineering Center (NSRDEC). “We want to offset that weight by reducing the number of batteries and by giving them recharging capabilities.”

In development since 2012, PowerWalk has passed through a number of studies already. A major field exercise at Fort Benning, Georgia, is planned for August 2017.
“For that evaluation, we want to see whether this device actually helps,” Soto said. “We know that radios and other devices consume a lot of power. We want to know how soldiers use this device to actually meet those needs.”

Most of the technology comes from the Vancouver, British Columbia-based firm Bionic Power Inc., which in mid-2015 won a $1.27 million Army contract for the work, following on an earlier $43.8 million award.

“The U.S. Army has a goal of harvesting 100 percent of the electrical power in the field for dismounted soldiers,” CEO Yad Harcha said in announcing the more recent award.” Bionic Power’s energy harvester is one of the few technologies in the world that can deliver this type of capability.”

How it works

PowerWalk, which looks like a typical knee brace and weighs less than two pounds, converts a soldier’s movement into energy. Walking at an average 2.5 miles an hour, a soldier could generate enough power to charge up to three phones, Soto said.

The human stride has a positive and a negative component. Muscles exert a positive force in lifting and thrusting the leg. Gravity then pulls the leg down, prompting the muscles to exert a negative force, acting as a brake to slow the descent.

“The PowerWalk adjusts to the user’s walk and on the negative cycle it helps you to brake,” Soto said. “As you step down, the system absorbs that energy and turns it into power and then when you lift, it shuts off, so the user does not get tired out.”

It’s meant to be almost transparent — and early tests show that it is, although the process is not yet seamless.

“Soldiers don’t want to put anything on their legs except their boots, so they all complain about it at first, but then they all forget about it after a couple of minutes,” Soto said. “It takes a few minutes to get used it, and it takes a couple of days to really master it. You have to learn to rely on it to help you brake, rather than forcing it.”
Still, this is all a big improvement on the state of the art just a short time ago.

“In 2012 this was still science fiction,” Soto said. “It weighed seven pounds, it looked like a medical brace, it felt like a medical brace. And it was unreliable. It broke down quite a bit.”

The technology breakthrough came when designers were able, after much experimentation, to engineer an extremely close fit between the device and the knee. “The hard part is mimicking human motion,” Soto said.

“This thing is right next to the knee, and coming up with something that could exactly mimic that motion is very difficult. The knee doesn’t pivot at one point. It’s more like a slide on a stick: The top part slides a little bit forward, and mimicking that notion is very difficult,” he said.

Now researchers think they have just about got it right, a device that captures the full range of motion and turns it efficiently into usable energy.

With the soldier’s variety of devices ever increasing, and with battery load rising in turn, the ability to leave backup batteries behind could be a boon to the foot soldier on the move, Soto said.