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.
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.
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?
" 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.
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.
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.
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