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That sure beats tying my wife to the car and having her pull it around town.She whines too much to enjoy the savings.
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I understand the goal and the article does say they expect to improve things. However, if I have to choose between a 1 kg device and 0.1 kg in battery weight, I will, for now, opt for the battery.  Harnessing the power of movement to power portable electronics: study
Fri Feb 8, 11:32 AM ET
Talk about multitasking. US and Canadian scientists have devised a new energy-capturing knee brace that can generate enough electricity to power a cellphone or any portable device that can run on a modest amount of juice, according to study released Thursday.
The brace harvests the energy lost when a human brakes the knee after swinging the leg forward to take a step in much the same way that a hybrid-electric cars recycles power from braking.
"There is power to be harvested from various places in the body, and you can use that to generate electricity," said Arthur Kuo, a co-author of the paper and an associate professor of mechanical engineering at the University of Michigan in Ann Arbor.
"During walking, you dissipate energy in various places, when your foot hits the ground, for example. You have to make up for this by performing work with your muscles."
In preliminary testing, volunteers with a device on each leg generated five watts of electrical power without breaking a sweat and they only used one watt of extra metabolic energy for each watt of electricity they generated.
The power the walkers generated was enough to power 10 cell phones at the same time and twice the power needed for computers in developing countries.
Expressed another way, one minute of walking would provide 10 minutes of talk time on a cellphone.
The prototype is a bulky 1-kilo (2.2 lb) brace equipped with a generator, but its creators hope to have something much lighter ready for tests in field trials in a year. They believe the device could be helpful to hikers or soldiers who don't have easy access to electricity.
"One of the biggest technological challenges for the military is developing a portable power source so dismounted soldiers can power their navigation devices, their night-vision goggles, and everything else they carry," said Max Donelan, a professor of kinesiology at Simon Fraser University in British Columbia, Canada.
The brace is the latest innovation in the field of energy-harvesting, which seeks to harness mechanical energy and convert it to electrical energy to drive portable electronics.
Researchers at the University of Pennsylvania, for example, are working on a backpack that converts the mechanical strain on the straps into electrical energy. The straps are made with a material that converts an applied stress into an electrical charge.
The study appears in the journal Science. Researchers from the University of Pennsylvania also worked on the project.
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The 1kg is a prototype and, who knows, the device may end up being about the same weight as a battery pack. The 5 watt output would work fine for an LED headlamp. But even better would be night-vision goggles which would even be better for the environment because they don't disturb anything with bright light. Seems like it's a long way off for hikers to routinely use night-vision goggles but maybe it'll come sooner than we think. Edit: Another article says it's heavier, "Though the prototype device weighs about 1.6 kg (3.5 pounds), Donelan believes commercial production units will end up weighing less than 1 kg (2.2 pounds)." http://news.yahoo.com/s/nf/20080208/tc_nf/58279
Last edited by Bob K.; 02/10/08 02:00 AM. Reason: as indicated
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Gee, does this mean that even more people can walk around with cell phones permanently mounted on their ear? 8^)
This sounds sort of gimmicky to me; While they equate it to generating power from braking on a car, that truly is lost energy, where I suspect this uses some of the walker's energy and so is nothing more than a variation of those hand-cranked radios and flashlights. I suppose it would be less monotonous to put out the effort while walking, instead of sitting there cranking, but I'm not sure I'm interested in walking around with generators clipped to various body parts.
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There is no such thing as "lost energy".There is always conservation of energy and mass.What you may be refering to is gaining energy through de-acceleration.
Last edited by DocRodneydog; 02/12/08 09:58 PM.
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There is no such thing as "lost energy".There is always conservation of energy and mass.What you may be refering to is gaining energy through de-accelerstion. You're right there, Doc; a better term might have been "wasted energy". That is, unless you are planning to heat up a burrito on the brake disc, in which case even that isn't wasting it 8^). Of course, if you use the braking energy to charge a cell phone so you can hike along in the wilderness (or supermarket for that matter)and jabber on the cell phone, then again it becomes "wasted energy"...8^)
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The 1kg is a prototype and, who knows, the device may end up being about the same weight as a battery pack. The 5 watt output would work fine for an LED headlamp. But even better would be night-vision goggles which would even be better for the environment because they don't disturb anything with bright light. Seems like it's a long way off for hikers to routinely use night-vision goggles but maybe it'll come sooner than we think. Suppose the device could be made with negligible weight. There are still other limitations. An average person walking along on flat ground at 3 mph burns about 300 W. He will start notice if some device he's wearing taps off more than a few percent of that. So this is not a solution for powering that plasma TV that you're all dying to bring along on your next overnight hike (it might burn 300 W too). It could come in handy as a battery charger for low power devices. But so could a good solar panel.
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Alan, That's a good point that it's not just about weight. Conservation of energy is a law that doesn't need enforcement. However, consider the device to partially replace the shock absorbing action of the knees when we hike so that it wouldn't require extra energy from the user and may actually reduce the energy that the user has to expend. In other words, hiking is a motion that consists of thrusting forward with one leg and braking with the other leg, and thrusting, braking, ... The device would be powered during the braking phase of each step, somewhat like a hybrid car converts the energy from braking into electricity. I think DocRodneyDog and Gary R touched on this idea.
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Conservation of energy is a law that doesn't need enforcement. Add that to the list that includes "Gravity. It's not just a good idea. It's The Law."  However, consider the device to partially replace the shock absorbing action of the knees when we hike so that it wouldn't require extra energy from the user and may actually reduce the energy that the user has to expend. In other words, hiking is a motion that consists of thrusting forward with one leg and braking with the other leg, and thrusting, braking, ... The device would be powered during the braking phase of each step, somewhat like a hybrid car converts the energy from braking into electricity. I think DocRodneyDog and Gary R touched on this idea. I actually think it's a cool idea and it might be useful. However, any advantage has to be weighed (literally in this case) against the alternatives. If a 70 kg person is consuming energy at the rate of 300 W, adding a 1 kg device increases his mass (and his power consumption) by about 1/70 = 1.4%. So, he consumes an extra 4 W. If the device generates only a couple of watts, he might want to consider carrrying a fraction of a kg in extra batteries instead.
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Right on Alan, and don't forget the additional food and water you're going to need to carry to produce the extra energy required to carry the device. It's a vicious cycle 
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This reminds me of a lecture on parametric excitation, in a dynamics class way back when. An example was given of the (then-new) self-winding watch, which had an internal weight that would oscillate from the natural swinging motion of one’s arm. The oscillation keeps the watch’s spring wound.
It was pointed out that the motion of the watch’s weight would make the person’s arm swing a tiny bit slower than it would if he were wearing a regular watch.
Extrapolating to the present case: The leg the knee brace is on goes slower, and the guy will walk in a circle and never get to the summit.
Last edited by Bob R; 02/13/08 05:52 PM. Reason: Clarification of effect
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Hi The real story is a guy from Kansas carries 5 gallons of light water to the summit of all the mountains on the way to Whitney then releases the water into a very large Pelton wheel he carried to the summit and collected the effluent back in the bucket ( no pun on the other turbine) and saved the stored energy for sale at a higher KWH, Oh he threw the Knee brace away in Utah and bought some batteries, one night as he was to meet Hayduke and the boys over there by Green River, heard there was some new thing called free heat for ever , But if the water is in motion will it stay in motion even if he tippy tippy toes? , this same guy one time caught a fish in the ocean and wanted to take it to Kansas alive this story is very long but he had the fish living in half salt water and half fresh water then all fresh water, then no water and the fish and the guy was walking along out in the fields one day the fish fell into a pond and could not swin and well died, This is what gave the farmer the ideal to carry the water to the summit of Whitney, Some where we should get a modus ponens or a modus pollen and several dictosimplicitors along the way. We could look at the other guy from Colorado that wants to lay copper bars in the freeway and turn the cars into generators as the travel along , only problem they can't stop and must maintain 60 cycles and be aware of the VAR loading during peak hours now that USA makes limited products cap/ind loading is not a factor ,but then the IR/2 LOSS and the EMF's that close to the shopping center are also factors, Simpler may be better. Thanks Doug
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"dictosimplicitors"...word of the year nominee.
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It seems like I misplaced a logical fallacy around here someplace. Doug, are you going to start selling those dictosimplicitors at the store this spring? They'd probably really help a lot of people with altitude sickness.
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What if you could recharge your GPS and your Steripen from your shirt? It sounds like they are a few years away from anything you will be able to wear, but they have figured out the hard part. http://www.foxnews.com/story/0,2933,330615,00.html
ELLS
ClimbMtWhitney.com
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I hadn't heard about the fish drowning, that puts a different light on things. I've always said that fish shouldn't be allowed to drive, not even a modus pollen with training wheels.
But in that case, there may be hope for this Knee brace thing to ease the traffic on Mt. Whitney. Just require that people wear one, and they'll just walk around the parking lot in circles until their permit expires. Problem solved.
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