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.
Wow, it's amazing when you actually think about the number of high-tech devices that the typical soldier carries and what kind of added weight that translates to in their packs. The biomechanical energy harvesting idea seems promising. I would think the typical solider engages in enough movement and activity during the day to harvest and create a sufficient amount of energy for this technology to really have an impact.
This boot is at the nexus of necessity and utility. Our soldiers sorely need a recharging solution for their many comms devices. I've read -- I think it was in book like Generation Kill and also War by Sebastian Junger (or maybe it was on the Military Channel) -- that our troops in Afganistan and Iraq, particularly those in Humvees, have had to get their own Duracells sent from home in care packages because their lack of access to recharging was such a problem. So this solution, if it can move from research to implementation, will be extremely useful.
You make a cogent point, Robtatnorcross. I'm now rethinking my original comment. Clearly the key design constraint for solider communications and other power (e.g., infrared night vision) gear should be weight and power consumption. Low-powered electronics might be able to reduce the demand for power and thus lengthen the amount of time between charges for batteries. However, certain things will be immutable. For example, you'll always have to expend a certain amount of rf power to remain in touch. (Even after spread spectrum and other tricks -- which are actually primarily for security, not power -- it is what it is.) As for the solar panels, they might work in a desert local, like Iraq. But what about at night and also in jungle environments?
While with General Dynamics, I had the blessed opportunity to interview soldiers, freshly home from Afghanistan tour of duty. Meanwhile, I’ve previously posted my strong opinion that Focus-Group Marketing to understand use-case ergonomics is a “Best-Practice” in Pre-Product-Design. So, I happily accepted the opportunity to show these soldiers our latest and greatest ideas for their benefit & safety; and did I get an ear-full!I will never forget the 23-year-old sergeant puffing a smoke and gruffly stating: “Look – I get deployed with 6 duffle-bags filled with too many pounds of CRAP, and frankly, if it ain’t bullets or water, I just toss it!” This was a new beginning in my understanding of SWAP – Size, Weight And Power. Now, while this Heel-to Calf gadget may seem clever to generate a few mW’s for battery charging, I grimly recall my sergeant’s scoffing for what I had earlier considered clever ….. and then I also remember hearing the troops say they could get new AA batteries at any outpost, even in Afghanistan. But recharging the custom lithium cell-packs was nearly impossible.
@JimT: That focus-group marketing stuff can really pay off. Surprising perspective from those soldiers--you falsely assume that equipping them with the latest and greatest technology is what they deserve and what they desire. I guess when you're right in the thick of it, survival and safety are all you care about (and rightly so) thus any kind of extraneous gear is at best, a nuisance, and at worse, a hinderance.
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...
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.
" our troops in Afganistan and Iraq, particularly those in Humvees, have had to get their own Duracells sent from home in care packages because their lack of access to recharging was such a problem."
ARE YOU KIDDING? This is an outrage and a disgrace to treat a soldier in this fashion. What? No charging outlets on a HUMVEE? You get more 12 volt outlets on any SUV.
And then we have to put the task of charging their batteries on their feet? We are supposed to do things to ENABLE, not hinder, a soldier. In an emergency this charger certainly makes sense but lack of access to recharging sounds like this is routine operating procedure.
How many millions will go into developing this when power outlets in every vehicle will go a long way to solving this problem?
While I'm sorry the condition exists in the first place, I'm not apologizing for the tone of this post. What kind of short sighted thinking leads to this? There needs to be more outrage about this.
My thoughts exactly. How often do we send soldiers out without a Humvee fairly close by. I suppose it happens and that when we need a charging device. I suspect that Humvees do have chargers.
@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.
Cool article. I wonder, though, whether the gadget on the boot makes walking harder. I also wonder how the energy is stored between the time it is generated by the walking and the time it is transferred to a particular device. Any thoughts on that Pat?
This looks like a great idea. Aside from questions about how much energy can really be harvested and stored, and how heavy the gadget is, I also wonder if the generator makes any noise? That could be a problem.
A few issues with this one. Article states a charge rate of 6-9watts/85minutes walking 3mph - enough to charge 2 AA cells. That sounds good enough, but in reality will take much longer because the average soldier will not be walking 85 minutes straight. He may be on his feet for hours, but not necessarily moving. Those charge times are best scenerio and I think misleading. Also, as someone who has been in Iraq pounding the pavement, I don't like the bulk and snag hazard of the unit. Open street walking is one thing, but climbing over obstacles, in and out of vehicles is another. I hope it works well in the field, but I would rather have a few spare AAs in my pocket rather than rely on this to "eventually" charge my cells.
This concept doesn't appear to make much sense. The target weight is stated as 430 grams and a Duracell AA weighs in at 23 grams, so essentially the soldier could carry at least 18 Duracell AA's instead of the complex arrangement described.Canadian built Duracell AA's were 1.5Wh units produced for the RCMP, so, high performance alkaline are available with their consistency and reliability. Moreover they can be carried bandolier style which foot soldiers will tolerate more so than some device clinging to their ankles.
a couple of comments: (1) this is not for the HumVee based soldiers, this is intended for Special Op's or Covert Actions where the only transport is by foot (2) you still have to carry a number of different size batteries to fit into the EH to capture the generated energy ( i.e. a couple of AA, C, D, 9V, etc) so you haven't gained all that much (3) the key to the success of this device is not how well it works but rather its ready acceptance and adoptability by those that use it-- the soldiers; just looking at the photo of the device its clear that those soldiers that were consulted in the design phase (and i'm being generous here) clearly never served in the field--I'd give the most tolerant and forward thinking soldier, who is wearing a 70LB pack and carrying a 50 caliber machine gun about 100yds before he tore this off and threw it away--and they are already finishing a Phase II for $750K and looking for investment for Phase III??
Don't get me wrong-- the concept is worthwhile, DARPA and DoD have been pursuing this for years, but this incarnation has got a real ways to go. Sorry :(
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?
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
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.
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.
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.
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!!!
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.
Actually, the article describes the energy harvesting to be in the "heel-strike" portion of the gait cycle; so, the extra 100# would add about 50% to the moment about the ankle (assuming solidiers are less than 200#), making the 6-9W about 2-3% of the maximum ankle power. We are collaborating on the opposite problem, providing power to the ankle for those with disabilities; and, this portion of the gait cycle will be harvested as well, though to a much smaller degree.
I suspect that this is just a step toward robotic solidiers anyway, for those instances where UAV's don't work.
Robotic soldiers--now that's a development I could get behind. Kind of like those soldiers/transformer-type robots that were part of the military crew in James Cameron's Avatar movie. Who cares if they get blown up. It's only money!!
This is really an impractical idea for the reasons other posters have mentioned.
Nevertheless, I would expect it to morph into an email coming our way shortly, in all-caps, of course, to the effect of "Obama forcing our heroes in Afghanistan to go green and recycle their batteries to keep the country pollution free"
You're right, Gusman, that's definitely coming. But assuming the foot generator doesn't impede movement -- or squeak too much -- it's quite a clever idea for helping the soldier to be self-sufficient out in the field.
It is also interesting to note that many semiconductor device manufacturers have come out with specific energy harvester IC, like Linear Technologies LTC 3588. This segment will definitely gather momentum. Success stories like that of solar impluse http://www.solarimpulse.com/ will act as catalysts in energy harvesting.
Applying this in the battlefield can be a great application, but civilian uses of this technology are also high. Imagine a running shoe with a similar technolgy that charges your Ipod or cell phone while you go running. This would be a geat way to stay green.
I agree, Tim, especially now that we have so many gadgets that need continual recharging. I would imagine if this opened up, there would be a wide range of applications to charge devices. Perhaps one of those hand-grip exercise tools that build arm muscle while producing electricity.
The picture reminds me of some boots that I once owned. I would like to see a race between somebody wearing them and an infantry-man weraing normal issue boots. Of course it is possible that they could run faster than I could while wearing safety boots.
Aside from that it does look like a potentially good idea.
The picture reminds me of some boots that I once owned. I would like to see a race between somebody wearing them and an infantry-man weraing normal issue boots. Of course it is possible that they could run faster than I could while wearing safety boots.
Aside from that it does look like a potentially good idea.
Last year I saw powered exoskeleton tests for the army. The exoskeleton was a load-bearing means. I suspect this might end up being more useful than energy boots. Note how much the soldier's load weight has increased over time. It's always going up. A small weight savings in batteries will be erased by other, new, absolutely necessary equipment.
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