Turning exercise into electricity—one step at a time

Larry Rome's Suspended-load Backpack

Larry Rome's Suspended-load Backpack has attracted interest from around the globe.

RESEARCH/This Penn biologist took just 30 minutes to invent a power-generating backpack.

In the middle of Larry Rome’s biology lab sits a treadmill. Overhead, a ring of high-tech cameras points down at the clunky piece of exercise equipment, and a computer nearby flashes a video of a man walking with an odd-looking backpack.

“The funny thing is,” says Rome, “two years ago, none of this stuff was here.”

Certainly, for much of his career in biology, Rome had little use for a treadmill, much less cameras like those Hollywood producers use to create special effects.

Just one phone call from the Office of Naval Research changed all of that.

Rome, a Penn professor of biology and an expert in animal locomotion, had been working with the Navy on a project to develop boats that could move like fish—which, says Rome, are built to move through water much better than even the sleekest ships—when Navy researchers presented him with another problem.

“This was around the fall of 2002. It was after 9/11 and the military was in Afghanistan,” Rome says. “This was the first war where they were relying almost entirely on Special Forces and high technology, and it was a big change in the way war was conducted.”

At the time, soldiers were carrying more high-tech devices than ever, but had no way of powering them except for batteries. And those batteries were proving burdensome.

“If these soldiers are out in the mountains of Afghanistan and they run out of batteries, they can’t just run out to the Wawa and get some more,” Rome says. “They were lugging around like 20 pounds in batteries.”

So the Navy asked Rome to come up with a way to convert the mechanical energy generated by walking soldiers into electricity that could be stored, and used, by those soldiers in the field.
The task fell far from Rome’s field of expertise, and other experts approached by the Navy had failed to come up with a solution. But Rome said he visualized a design in less than an hour—a design he was certain would work.

The result is the Suspended-load Backpack, an ingenious invention that uses a person’s natural walking motion—and the weight of a loaded backpack—to generate about 7.5 watts of electricity. That’s more than enough to power several portable electric devices all at once.

“It took some creativity and the right background,” says Rome. “But it is true that I had the idea in my head in about half an hour.”

The most impressive thing about Rome’s backpack may be its simplicity.

Told that soldiers often carry loads of about 80 pounds, Rome says he decided immediately to “put that 80 pounds to work.” And that’s the key to the pack’s success.

The Suspended-load Backpack is built on a rigid frame, but the load in the backpack is actually suspended from the frame by a series of vertical springs.

This set-up allows the load to “bounce” up and down as a person walks forward. A small generator attached at the top of the back captures that “bounce” and converts the motion to energy—more energy, in fact, than the Navy had hoped for. They asked Rome for about one watt, which is the amount of energy needed by a cell phone or night vision goggles.

The invention may never actually be put to use by the Navy—the point man for the project has since left the service, Rome says—but the prototype has generated more than a little buzz anyway, Rome says. The backpack has received more press coverage than any of his previous work—a recent article even appeared in a Korean newspaper—and has produced inquiries from across the globe. He’s gotten emails from as far away as Mozambique from people curious about the pack’s prospects, and Rome says he’s especially hopeful the invention could be put to use by humanitarian organizations working in remote areas.

“It’s been bizarre,” Rome says. “I didn’t even work in this field. I have no idea what people in this field are interested in. But I just put my blinders on and did my thing.”

Originally published on October 20, 2005