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.
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.
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.
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.
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.
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.
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.
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!!
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.
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"
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