As soldiers carry more portable electronics, battery weight becomes an issue. On a 72-hour mission in Afghanistan, a US soldier will carry 70 batteries for such devices as night-vision optics, GPS, imaging systems, and communications gear. This adds 20 pounds to a combat load, one-fifth of total weight, says the US Army Research Laboratory (ARL). The load can contribute to fatigue and affect movement during combat. On the cost side, an infantry battalion spends $150,000 per year on batteries, its second-largest expense after munitions, ARL reports.
Sustainable power sources are thus high on the Pentagon’s must-have list of soldier technologies. One promising concept is biomechanical energy harvesting, in which body motion generates electricity. SpringActive Inc. of Tempe, Ariz., is developing such a device, which it calls SPaRK -- Soldier Power Regeneration Kit -- with funding from the Army’s Natick Soldier Research, Development, and Engineering Center in Natick, Mass.
The SPaRK biomechanical energy harvester produces 6 to 9 watts of continuous electricity from walking. (Credit: SpringActive Inc.)
The device generates and stores electricity as a soldier walks. Jeff Ward, a partner and senior engineer at SpringActive, says that at 3 mph, both legs continuously generate a total of 6 to 9 watts, enough to recharge two AA batteries after 85 minutes. This is a good result, he says, and is achievable because an electromechanical generator is used for power generation instead of piezoelectric crystals, which produce lower output.
The initial design uses an exostructure that attaches to a soldier’s boots. Ward says SPaRK will become an integrated component, which will be more comfortable to wear. Initial data shows “no significant increase in metabolic cost for harvesting energy while walking at 3 mph,” he adds.
The main components include a Kevlar pull cord, a ball screw with 1mm pitch, a spring, and a motor/generator. (In this design, exciting motion in the motor collects energy, whereas in most motors voltage is applied to produce motion.) The device is activated by the energy generated by the user’s gait.
The generator is above the ankle and attached to the pull cord, which is affixed to the heel. After a heel strike and about 20 percent into a gait cycle, the cord, also connected to the ball nut and spring, is pulled taut by the generator as the tibia moves forward over the ankle joint.
Dear Azny - I failed to note that I was only adding the wheel assembly/generator to the pack. Straps and all would remain for travel on non-paved trails. Not ever a grunt, I can't say how much walking is on pavement. But I'm sure 100# doesn't add much energy to the soldier. I'd hate to back-pack my luggage through an air terminal.
good thought, nice try Mex-- but no dice!!--imagine pulling a wheeled pack up a steep rocky incline of 30 degrees in Afghanastan, not only do you have the 100# pulling you backwards, your wheels will get stuck. and a squeek of the wheel on a silent mission would be deadly.
if it wasn't so serious it would be hysterical to see a platoon of troops running around like 3rd graders pulling their wheely backpacks, or airline passengers scrambling with their rollies--- gotta be a scene somewher in Stripes!!!
AW-- HumVees have chargers in them, equipment checks prior to mission deployment require the soldiers to make sure things are charged up. If during the mission the IR loses power, the good soldiers carry on ( after all, battles have been fought for hundreds of years without IR at night) the poorly trained ones sit down and cry!!-- US forces thankfully are well trained
Take heavy packs off backs. Then put wheels on them. Each axle could drive a small generator while making combat postures possible. Drop the pack handle and grab the rifle. Much simpler than untangling from two pack-straps to fight. Save energy by pulling the pack while charging cells.
@George Kaye. You are so right. Does this not sound so typically bureaucratically government? If the problem is batteries then find a way to get the troops batteries. Not some fancy doodad that is going to add wieght and effort to his job.
The article says 20 pounds of batteries, "about 1/5" of his equipment weight. That means each soldier is carrying 100 pounds. It was another war and a whole different army, but when went on an operation with rations for 3 days, our own ammo, 200 rounds for our M-60, claymore mine, flares/smoke, and a LAW my rucksack wieghed in at 70 pounds and kicked my tail. By the end of the day very few of us were in a combat ready state. I question the extra 30 pounds in this article. If there is indeed 30 more pounds today, then that should be the first order of business: get some of that weight out of there.
Get the device off the foot and put it in a kneepad that most of the soldiers wear anyway. Make it a hybrid knee "orthotic" & workmans kneepad that can be worn externally on the leg. It'll be much easier to access in situations where you can't reach all the way down to your ankle to locate a new battery.
In all of these energy harvesting schemes, consideration must be given to: The cost /benefit of a device including weight, ease of use, reliability and other factors versus the actual energy recouped. For the few watts recouped, the user (the dog-face hauling it around) has a bulky gizmo that may affect agility when climbing terrain and urban rubble, and increase the effort to walk. Remember, that harvested energy has to come from somewhere.
This deal reminds me of a project I consulted on: the client wanted to attach wind turbines to an electric automobile to recoup energy to help charge the car's batteries. A simple paper analysis showing the fallacy of his idea wouldn't do, so he bought an electric vehicle and paid me to prototype and test wind turbine generators that, as predicted, didn't cut the mustard.
Azny and Criteria Dependent, I'd like to thank you both for your experienced-based perspective. Re Azny's comment about the variety of batteries and HumVees, that's exactly what I was trying to get at in my earlier comment, though I missed the mark. What is the solution for HumVees? What do HumVee-based troops do when, say, their IR vision equipment runs down?
Agreed, As a former infantryman, I can see this unit seriously hampering forward progress. Especially walking in mountainous and rocky terrain. I agree with the previous post, a sealed unit in the sole of the boot might be a better approach.
Why such a Rub-Goldberg contraption? Put a closed loop air cushion ( piston ) in the heal of the boot to both soften the walking shock load and apply the downward walking pressure (kinetic energy) to drive the generator through hydraulic principles. All contained inside the heal of the boat for a sealed unit...
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