Anyone who has tried running while wearing a backpack knows how cumbersome a small load can become even after a short distance.
On the battlefield, troops carry as much as 80 pounds of battle gear and they lug an additional 20 to 30 pounds of batteries to power their portable electronic devices. That weight is so problematic that “lightening the load” has become the ground forces’ mantra. But efforts to reduce weight have been stymied in part because troops need sufficient power for their equipment — energy that only comes from heavy batteries.
Finding a way around that conundrum has been a technological challenge. But researchers at the University of Pennsylvania have developed a rucksack that may soon allow troops to not only charge up their radios, night vision goggles and GPS units on the move, but also ease the weight problem.
Based upon a standard rigid-frame pack carried by hikers, the electricity-generating backpack produces power from the mechanical energy created by a person walking or running.
If troops are carrying 80 pounds of equipment on their backs, the energy that goes into lifting that heavy load is 40 watts of mechanical energy, says Larry Rome, a professor of biology at the university who developed the technology with a grant from the Office of Naval Research.
“If we can capture a small amount of movement as they step and walk and lift the load, then we should be able to generate much more electricity than we ever have before,” he says.
When a person walks, the body bounces up and down about two to three inches. A backpack, including the contents, also moves the same distance.
For the electricity-generating backpack, university researchers have separated the cargo compartment from the backpack’s frame. Using springs, the compartment is suspended from the frame, which allows the load to move up and down at a slightly different pace. The load’s movement turns gears located on the frame, which connect to a generator that produces the electricity.
“The more load you carry and the faster you move, the more electricity you can generate,” says Rome.
The latest version of the backpack can generate 20 watts of electricity. Most of the portable electronics used by the military operate on less than half a watt of electricity.
“Our device will power equipment in real time,” says Rome, who founded the company Lightning Packs LLC, to continue with the development. Any excess energy can be collected and stored in capacitors or a battery for later use.
The researchers are still developing the interface for connecting the backpack to the various electronic devices. Options under consideration include charging the gadgets directly from the backpack using cables or creating standardized batteries for the various electronics.
“We anticipate that there will be one large rechargeable battery, and the electricity would be distributed from there,” says Rome.
Under a different contract from ONR, the scientist has created another similar unit, called the ergonomic backpack, which doesn’t produce electricity but reduces discomfort.
For example, if you have a 50-pound load in your backpack, it exerts 50 pounds of force on you while standing still, Rome says. When you run, the peak force increases to as much as 150 pounds.
By being suspended on bungee cords, the ergonomic backpack remains at a constant height above the ground. That reduces the accelerative forces on the wearer by 82 percent during walking and by 86 percent during running.
For the same amount of metabolic effort it takes to carry 48 pounds in a regular backpack, a person can carry 60 pounds in the ergonomic backpack, he says.
The electricity-generating backpack also contains some inherent ergonomic benefits. The pack’s spring-suspension system reduces the accelerative force by about 30 percent, Rome says.
In the future, the two concepts could be merged into a single backpack. If troops want more ergonomics and less electric generating power, the scientists are confident they’ll be able to tweak the technology to cater to their exact specifications.
“Not only do we feel that this will improve performance in the field, but it will also reduce acute injuries and long-term injuries after they have retired,” says Rome.
The backpacks also have appeal to first responders and humanitarian assistance workers who may be operating in locations where electricity access may be problematic, he adds.
The Office of Naval Research will test the backpacks in the coming year.