Ward says that energy capture begins when the shank of the leg is perpendicular to the foot, or just before. As the cord goes taut it extends the ball screw, which in turn compresses the spring. This action by the ball screw produces energy by spinning the motor/generator at a high rpm and at the same time stores energy in the spring. When the foot pushes off for another step, the cord goes slack, releasing the ball screw and decompressing the spring, which releases its energy into the motor/generator. The sequence repeats in the other leg.
The original version of SPaRK weighed 1.4 kg (3.08 lb), but Ward says the current version is 860 grams (30 oz), and believes it can be reduced to 430 grams.
Ward says that in emergencies more metabolically taxing motions would produce greater amounts of energy. Standing in place and doing knee bends could generate 26 watts, enough to power a radio or, possibly, get a networked soldier back online.
Such an action may seem difficult, but Ward says that for soldiers on a battlefield with no other means of activating critical electronic systems, it would be an important option.
As for the 85 minutes it takes to recharge two AA batteries, Ward says that with a comfortable and lightweight SPaRK system, walking that long wouldn’t be a problem on multi-day missions.
The power generated tends to come in bursts rather than an evenly regulated flow, due to the mechanics of walking. Ward and his team have built a capacitor circuit that filters these energy spikes into a usable form for recharging AA batteries. The next phase will be to improve the efficiency of the charging electronics.
The project is concluding its Phase 2 SBIR (small business innovation research) design stage. SpringActive is seeking additional funding for Phase 3. Depending on the funding award, Ward says, the company could within 12 months build several prototypes for field-testing by the Army.
“Soldier load is a huge issue,” Ward says. “As troops become more networked, power demands go up. There will have to be some technologies to meet this demand without increasing the number of batteries a soldier carries. Harvesting energy at the ankle is a great way to do this.”
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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