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Power Biotech

Knee Brace Generates Electricity From Walking 128

Posted by Soulskill
from the runs-on-walks dept.
ktulus cry brings news of a device that can power portable gadgets, prosthetic joints, and other mobile appliances by harvesting energy generated by walking. Researchers are working on making the device — still a moderately cumbersome 3.5 pounds — smaller while maintaining its energy harvesting capacity. CNet has a write-up with more pictures and a diagram of the device. "In the mode in which the brace is only activated while the knee is braking, the subjects required less than one watt of extra metabolic power for each watt of electricity they generated. A typical hand-crank generator, for comparison, takes an average of 6.4 watts of metabolic power to generate one watt of electricity because of inefficiencies of muscles and generators. A lighter version would be helpful to hikers or soldiers who don't have easy access to electricity. And the scientists say similar mechanisms could be built into prosthetic knees other implantable devices such as pacemakers or neurotransmitters that today require a battery, and periodic surgery to replace that battery."
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Knee Brace Generates Electricity From Walking

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  • by MPAB (1074440) on Sunday February 10, 2008 @11:06AM (#22370154)
    by walking under heavy rain?
  • by ScrewMaster (602015) on Sunday February 10, 2008 @11:11AM (#22370174)
    A lighter version would be helpful to hikers or soldiers who don't have easy access to electricity.

    Sergeant: Private!

    Private: Sir!

    Seargeant: Walk faster! We're trying to reach HQ.
    • Re: (Score:2, Informative)

      by hazem (472289)
      Good joke, but just an FYI, privates don't "sir" sergeants, seeing that sergeants work for a living.

      (In the US Army, at least, "sir" is reserved for male officers and warrant officers.)
    • by eonlabs (921625)
      Those neurotransmitters are a bitch to keep powered all the time. Damn, most of my classmates and coworkers clearly had difficulty with keeping theirs up and running. I'm sure many people can say the same.
  • by iknownuttin (1099999) on Sunday February 10, 2008 @11:11AM (#22370180)
    Walmart customers, I think if we can get them walking with these on, we'll solve all of our energy needs! Think about it. The entire country powered by fat, Cheetoes, Doritoes, Beer, etc.... And, with all of these large folks walking, they'll be in better health and therefore reduce the burden on our health care system ( one of the biggest expenses the Medicare has to deal with is kidney dialysis because folks fry their kidneys from hypertension. ).
    • by ddrichardson (869910) on Sunday February 10, 2008 @11:41AM (#22370394) Homepage

      A study in Holland [plosjournals.org] disagrees about the savings from obesity reduction:

      Conclusions

      Although effective obesity prevention leads to a decrease in costs of obesity-related diseases, this decrease is offset by cost increases due to diseases unrelated to obesity in life-years gained. Obesity prevention may be an important and cost-effective way of improving public health, but it is not a cure for increasing health expenditures.

      • by snl2587 (1177409)
        But...what if we used them as fuel? I'll bet the researchers didn't consider that!
      • A similar thing is going on with anti-smoking campaigns and mandatory seat-belt laws. With less people smoking, there are less people dying earlier of lung-related illnesses. With mandatory seat-belt laws, we're seeing a decrease in the number of viable organs for organ donation.
      • I've seen that. It's very interesting. I think what's really ironic is that the tobacco companies have done a similar study (This is the closest I could find after several pages of Google hits [cnn.com]) a few years ago and it was a PR disaster for them. But now, a similar study regarding obesity has come to the same conclusion that early death benefits society but without the PR disaster. Interesting isn't it?
        • I think its fairly obvious why its was a PR disaster and it has nothing to do with double standards if that is what you are getting at. The tobacco companies were making money from their product which was killing people, and the best they could come up with was "well by killing 'em early money is saved!"
      • I've heard smokers make the same argument. By dieing young they save the NHS money in expensive geriatric care. It's probably true, since it's far cheaper to let someone die untreated of something essentially untreatable like lung cancer or a sudden heart attack than it is to keep them alive for years in a old people's home.

        Not that the NHS sees it that way of course, they're discussing refusing operations for people who are obese or smokers. [independent.co.uk]. Not all people with self control issues are punished though. Her
      • Re: (Score:3, Interesting)

        by TheLink (130905)
        I'm not a smoker.

        But that's why I don't understand why so many of those socialist european countries are so against smoking, when they are so worried about "aging population" and creaking health services.

        Sure discourage people from smoking, and educate them on the dangers. But don't make it impossible.

        Tax tobacco enough and the smokers pay for their own "funeral" and everyone else's :).

        If smokers survive past retirement age, they'll still be paying tobacco taxes. Give the best "donors" a cert of appreciatio
      • by edcheevy (1160545)
        I could see where a long term healthy person might cost more than a short term obese person, but did they include the extra taxes and/or health insurance premiums a person might generate if they didn't die of a heart attack at 40?
      • by Sandbags (964742)
        Incorrect. Where it is true that diseases and health issues later in life will be encountered by those who survive obesity by conquering it, and thus extending their life, you neglect serveral facts:

        1: medical costs for those that reach higher years in life are usually short lived, predictable and the cost is relatively minimal for most people. Heart attacks and strokes, of the most common ways to die in old age, happen suddenly, and do not have extreme costs associated with either recovery or death. Con
    • by g0dsp33d (849253) on Sunday February 10, 2008 @11:58AM (#22370544)
      I wonder how long until they pair this with a water tight hydration recycling suit and we chase worms in the desert?
    • Walmart shoppers can walk? Most I see park in handicapped and get around on tiny electric scooters.
    • Perhaps they should therefore invent a dynamo-wired fridge door, beer can ring pull, or perhaps a sofa cushion...
    • In The Dilbert Future, Scott Adams suggested the logical consummation of this, and really the most complelling way of harnessing "stupidity for clean power(tm)".

      The proposal is pretty ingenious: First, you build a bunch of large hamster-wheel type contraptions in front of gas stations and convenience stores. The energy generated by people running in the wheels is hooked either to the grid or electrolysis for Hydrogen production. Then, you offer a 10 free lottery tickets per every 15 minutes in the wheel.
    • by KefabiMe (730997) <garthNO@SPAMjhonor.com> on Sunday February 10, 2008 @06:24PM (#22374138) Journal

      Actually, there is concern that this device may cause muscles to atrophy. It works by helping slow down your leg during the part of each step where your quadriceps "slow down" your leg. Similar to how electric cars use "regenerative breaking" to slow the car down and gain back energy.

      In fact, theoretically when this device gets light and exact enough, walking can take less effort than without the device!

  • Care to explain how this statement, as it stands, does not conflict with the 2nd law of Thermodynamics?
    • by Burdell (228580) on Sunday February 10, 2008 @11:15AM (#22370214)
      It is less than one watt of extra metabolic power when braking. I would assume (without RTFA) that this is analogous to regenerative braking in electric/hybrid cars.
    • by maxwell demon (590494) on Sunday February 10, 2008 @11:17AM (#22370226) Journal

      Care to explain how this statement, as it stands, does not conflict with the 2nd law of Thermodynamics?

      That's simple: They violate the first law of thermodynamics, not the second one.
    • Re: (Score:2, Informative)

      by TheEmptySet (1060334)
      It generates energy as the knee is using energy to slow your downward motion, hence the statement "less than one watt of EXTRA metabolic power for each watt of electricity".
    • by vertinox (846076)
      Gravity.

      Walking and running is a controlled form of falling forwards.

      Maybe .75 watt of metabolism to lift foot up met by .75 created by gravity where .5 is wasted due to heat and other forces leaving 1 watt left over?

      Of course someone might be calculating a metabolic watt different from a plain old electrical watt for some reason.
      • by jadavis (473492)
        Walking and running is a controlled form of falling forwards.

        I've always wondered what people mean when they say that. Is standing still a controlled form of falling as well? What if you walk sideways, what's that? It seems to me that lying down must be a controlled fall, because you actually end up at a lower potential energy state, without ever losing control of the states in between.

        So is there some kind of scientific basis for your statement? Or is it just one of those things that one person says, and e
        • Re: (Score:2, Informative)

          by heinousjay (683506)
          They're all controlled falls. Try doing any of those things without using gravity.
          • by jadavis (473492)
            Then anything that depends on gravitational force is a controlled fall?

            If that's the case, then calling walking a "controlled fall" is meaningless (or nearly so).
            • I wouldn't say it is meaningless, it helps to describe the forces involved in bipedal locomotion when compared to other forms of locomotion.
              • by jadavis (473492)
                What other forms of locomotion? All surface locomotion, as far as I can tell, depends on gravity.
  • Well... (Score:5, Funny)

    by vertinox (846076) on Sunday February 10, 2008 @11:13AM (#22370192)
    Thats neat. But wouldn't it be more efficient for us slashdotters if it was put on our arms... Depending on which one is using the mouse... Or... Umm... The one not holding the lotion bottle?
  • In the mode in which the brace is only activated while the knee is braking, the subjects required less than one watt of extra metabolic power for each watt of electricity they generated.

    Sounds like a violation of energy conservation.
    • Re:Perpetuum mobile? (Score:5, Informative)

      by antifoidulus (807088) on Sunday February 10, 2008 @11:53AM (#22370494) Homepage Journal
      Someone needs to work on their reading comprehension skills:

      In the mode in which the brace is only activated while the knee is braking, the subjects required less than one watt of extra metabolic power for each watt of electricity they generated.(emphasis mine)

      That means that the system captures some of the energy that would normally be "wasted" and converts it into electricity instead....
      • I wonder how much energy would be generated by a hip brake as I perfect the ass groove in my office chair all day...

      • by Snuhwolf (1105289)
        Why not self contained hydraulic pumps in the heels of army boots that drive a small turbine when weight is transfered to the heel?
        That would require no extra energy expenditure. Assuming of course they were being worn on earth where theres some gravity...
        • by fabs64 (657132)
          There was an article about doing just this a while back actually.

          From memory they had to use piezo's so the energy generated wasn't that great, still interesting though.
    • by MrMr (219533)
      No, the university press release claims that the energy is collected from otherwise dissipated heat.
      Sounds more like Maxwell demon ...
      • Re: (Score:3, Informative)

        by KiloByte (825081)
        Not exactly. The Maxwell demon takes what already is heat, these braces take what would turn to heat if unharvested.
  • by imsabbel (611519) on Sunday February 10, 2008 @11:14AM (#22370204)
    Knee Brace makes walking harder - Segway sees potential market opening
    • by Deadstick (535032)
      Segway sees potential market opening

      Not Segway, Nautilus. Put an assembly of these suckers on all your major joints, dump the generated power into a resistor, and you have an exercise machine.

      rj

    • Re: (Score:1, Redundant)

      by KefabiMe (730997)

      This device theoretically can make walking easier! It works by helping slow down your legs during each step. But the key point is that it only turns on during the part of your step where your muscles would be trying to slow down your leg anyway! (Similar to regenerative braking in electric cars.) So technically, this will make walking take less effort, not more!

  • At least this finally makes some sense out of Naked Snake's whole "walk around to recharge the battery" thing. Does this device generate enough power to operate a soliton radar?
    • by pizzach (1011925)
      I do believe I remember someone saying on slashdot.jp yesterday something about 5 min of walking = 1 hour of battery time for a standard cell phone. So I would say probably.
  • by moseman (190361) on Sunday February 10, 2008 @11:25AM (#22370282)
    When someone comes up with one that can convert talking into usable energy, let me know. I have several women in my office that could generate enough power to light a small country!
    • Walking/running roughly burns one calorie per pound per mile. You need to burn roughly 3500 calories to lose a pound. The average basal matabolic rate in an average person burns about 1500 calories So a 330 pound person, could subsist on vitamins and water, and walk across the entire USA, and arrive at a svelte 120 pounds.
      I picked a reasonable pace of 3 MPH for 15 hours a day, which would get you across the country in 66 days, using an additional 28 pounds for the basal metabolic rate.
  • by Raleel (30913) on Sunday February 10, 2008 @11:29AM (#22370318)
    it's so heavy right now because they made all the parts easily replaceable to the scientists working on it. The scientist they interviewed on it also mentioned that if you stop wearing it, you tend to swing your leg harder for the first 3-10 steps, unaccustomed to the now-unpresent braking by the device. Really neat idea... while it makes sense to me, I didn't realize we actually braked our legs as we walked forward.
    • by gotzero (1177159)
      Maybe it could be used to build muscle too. Go for a jog down a hill and you will feel your legs braking quite a bit. Hopefully they are able to make it a little less intrusive, and very inexpensive.
  • Someday all that exercise equipment in gyms will reclaim all their expended human energy into powering their own devices. Since even top performers like Lance Armstrong produce only 500W for under 20min [active.com], maybe we can just hope that exercisers can work off their lighting bill, if not heat their showers.

    Hikers with a body suit, though, might be able to cook their dinner.
    • Someone who exercises 1,000-1,200 Calories(that's a big C so we're talking 1.0-1.2 million one ml by one degree calories or 20 litres by 50 degrees) makes plenty of heat for a nice hot shower. For me this is about an hour on the stair climber or an hour and a half in the pool. As far as output to the machine it's only 2-250 Watt-hour but the heat energy is all there. Aside from getting ones exercise by swimming, I don't know of a good way to capture all that heat.
    • Actually, most gyms already do this - if you haven't noticed, most modern gym equipment (bikes, rowing machines, etc.) doesn't start up until you start using it.

      Now, if we could find an efficient way to extract the extra heat produced during exercise from the human body, that would be awfully cool - the human would be able to perform longer, and the heat could be used for something useful. Turns out the human body is a terribly inefficient heat engine - according to NASA SP-3006 (I research human power as
      • Re: (Score:3, Informative)

        by Mendenhall (32321)
        On the efficiency of the human body as an engine, the number you quote is about right. However, assessing that as a terribly inefficient heat engine is a bit odd.

        A really well-tuned automobile engine, running on pre-refined fuel, might get 40% thermal efficiency or so. The human body, of course, starts with rather unrefined fuel (food, to the non-techie :-) ), runs all the necessary chemical conversion machinery, and produces its output. It also expends a lot of energy in self-repair and maintenance, whi
      • by Doc Ruby (173196)
        Gyms have lots of lights that are on even when the gym is empty, or when people are taking a rest. I think their body work could power those lights pretty well, offloading from the grid quite a bit.

        Maybe there's a way to capture that waste body heat to heat up the water in the showers that people take after exercising. If the mechanical work is captured efficiently as power for lighting, then those gyms could nearly disappear from the grid, except as backup. The elevators in NYC gyms probably keep the energ
          • by Doc Ruby (173196)
            How does an article demonstrating that people are actually doing this show that people likely won't do this?
            • http://www.google.com/search?hl=en&q=define%3A+skim [google.com]
              the relevant result
              "to quickly read something to get a general idea of its contents"

              if you skim the link I posted, you'll find the well reasoned on topic posts indicate,
              "it's not going to work."
                the amount of energy required for just lighting is not going to be recovered from the equipment.

              • by Doc Ruby (173196)
                If you look at the 16 posts rated at 5 (I'm not going to "skim" hundreds of Slashdot comments just to find a point that you are trying to make), there's a few that are actually on-topic, but they mostly don't really show good reasoning applicable to what I said. Because I didn't say that $15K exercise bikes should run 100W incandescent bulbs. And if you look at the person actually talking about their own human power that they've analyzed carefully, they have a good argument even in that other context.

                If we
                • I guess the real problem is with my original short reply.
                  instead of "Likely no" I should have been more clear.

                  so specifically, to the comment" I think their body work could power those lights pretty well, offloading from the grid quite a bit."

                  my response should have been, "likely no, it will only offload from the grid by a tiny insignifcant useless amount, so small that even
                  the cost of setting up the equipment will be more expensive in terms of energy generation to make the changes, and connect the device
                  • by Doc Ruby (173196)
                    I'm talking about offloading from the grid quite a bit of the power required to run the lights for the people in the gym. If they're outputting even 150W, then the question is just how many watts of electric light do they consume, and what's the efficiency of the conversion of their mechanical power to electrical. If the efficiency is only about 66% (probably it could be much higher), then 100W is available. If each person is using 4 60W bulbs, then they can contribute 100/240W, or 41% of the power, which i
      • Re: (Score:3, Funny)

        by snl2587 (1177409)

        Now, if we could find an efficient way to extract the extra heat produced during exercise from the human body...

        I have an idea: we could put the humans in a little shell that captures their heat energy as they go about their lives. Come to think of it, it would make more sense if they were sedentary....and we could feed them through tubes....and make them think they were living free....oh, nevermind.

  • Oh. Oh, I see. Running away, eh? You yellow bastards! Come back here and take what's coming to you. I'll bite your legs off!
  • I've found the solution to several problems at once: Exercise plants!

    This will
    • generate jobs for unlearned workers, thus reducing unemployment
    • increase the health of those workers
    • reduce the reliance on oil
    • fight global warming, because the energy comes from food, that is, from regenerative sources


    SCNR :-)
  • In the mode in which the brace is only activated while the knee is braking, the subjects required less than one watt of extra metabolic power for each watt of electricity they generated. A typical hand-crank generator, for comparison, takes an average of 6.4 watts of metabolic power to generate one watt of electricity because of inefficiencies of muscles and generators.

    That is a bogus comparison, the arm and leg muscles are too different. A fair comparison might be bicycle based generator. Junk like thi
    • by gbjbaanb (229885)

      Well less than one watt in and a full watt out makes me think not science as well.
      statements like that make me think: try actually reading the article instead of just looking at the pictures.

      the subjects required less than one watt of extra metabolic power for each watt of electricity they generated.
      • "Well less than one watt in and a full watt out makes me think not science as well."

        statements like that make me think: try actually reading the article instead of just looking at the pictures.

        the subjects required less than one watt of extra metabolic power for each watt of electricity they generated.


        Try thinking harder. Your logic seems to assume that there is sufficient kinetic inefficiency to make up the difference. While this may be true for cars it is unlikely for a biological organism that
    • I think it was a fair comparison. How portable is a bicycle based generator? That and I imagine more people have been exposed to hand crank generators than they have bicycle based ones. It also doesn't say the device takes in less than one watt for every watt it puts out. It says the device required less than one watt of extra effort on the part of the wearer to get one watt out. In other words it's capturing some of the energy that would have been wasted anyways.
      • I think it was a fair comparison. How portable is a bicycle based generator?

        Smaller than a hand crank, and they generate enough energy to power a headlight. And that was with 1970s tech.
        • Really? I could be mistaken then. I would have assumed the pedal on a bicycle based generator would have been bigger than the whole unit for a hand-crank one.
          • Really? I could be mistaken then. I would have assumed the pedal on a bicycle based generator would have been bigger than the whole unit for a hand-crank one.

            One implementation of the generator is a device that makes contact with a wheel and spins as the wheel rotates. These are very small devices. With regard to making a bicycle a stationary generator a hole and some minor carpentry skill will accomplish that. However I think that is a tangent. If you are going to walk to generate power you could proba
      • It also doesn't say the device takes in less than one watt for every watt it puts out. It says the device required less than one watt of extra effort on the part of the wearer to get one watt out. In other words it's capturing some of the energy that would have been wasted anyways.

        Their measurements are naive. Respiration only indicates total energy consumption. It does not indicate a reallocation of energy within the body, for example digestion may have been slowed to provide additional energy. Further
  • by Anonymous Coward
    A use for Heather Mills! [wikipedia.org]

    Anybody got a whip?
  • by roman_mir (125474) on Sunday February 10, 2008 @12:04PM (#22370588) Homepage Journal
    As a guy who has had constant pain in his knees for the past 7 years, I am warning you that something like that may permanently damage your knee joint by simply forcing a minuscule change to the way your knee rotates while walking. I mean if unfitting shoes can hurt your knee, foot and hip joints (and they can) then this device may certainly hurt all of those joints as well if it forces you to change the way your legs are naturally moving.

    Don't damage your joints, the pain may last for the rest of your life.
    • I've got a messed up knee; and, I wear a brace to do any serious hiking or similar activity. Since I've already got the damn itch, sweaty, annoying thing on; it might as well serve two functions instead of just one. Power and joint stabilization seem like a nice deal for those who need the stabilization in the first place.

      For those whose knees are fine, however, it seems likely that the discomfort of any brace will outweigh the minimal juice provided. Carrying a supply of spare NiMH or other rechargeable

    • Re: (Score:2, Funny)

      by Cousin Scuzzy (754180)

      As a guy who has had constant pain in his knees for the past 7 years, I am warning you that something like that may permanently damage your knee joint by simply forcing a minuscule change to the way your knee rotates while walking.
      The article states that the brace is activated only while the knee is breaking. Of course it's going to be painful if your knee is breaking. Duh...

      What's that? Oh, braking...

      Never mind.
  • it makes us look more like the Borg.
  • Yawn - the Economist had an extensive article on this last week.

    It is sad when we get scooped by a large conservative economic journal that is only periphally concerned with technology.

    If the fanboys on this site could focus on posting something besides "Linux is better than evil Microsoft" we might get Slashdot back to being the premier site for propagating techy news for geeks.

    • Your joking? A one watt solar cell would be a lot less intrusive.

      Might I suggest the authors had this device strapped somewhere else, and that they now all need glasses. (As per the old joke ... can I do it until I need glasses.)
  • Really horrible idea, good knees are what people miss the most as people get older. I wouldn't want to trade 10 years of good knees just charge up my cell phone. Furthermore if I was a hiker or soldier walking all day, I wouldn't want extra stuff attached to my leg actually impeding my leg movements for a few extra watts of electrical energy.
    • I wouldn't be so quick to dismiss this gadget. There is a good chance that the stabilizing function of this generator far outweighs the extra pressure exerted on the joints.

      >>Furthermore if I was a hiker or soldier walking all day, I wouldn't want extra stuff attached to my leg actually impeding my leg movements for a few extra watts of electrical energy.

      Would you rather have 10 pounds of batteries to power your radio, stove, lights, PSP, etc., or 1-2 pounds of knee brace that actually stabilized your
  • by thewils (463314) on Sunday February 10, 2008 @12:23PM (#22370754) Journal
    If you could develop a smaller one that fits over a beer-drinker's elbow.

    Or how about a micro one that works off a woman's jaw muscles? No, wait, that means their cellphone batteries would never quit. Yikes!

  • My campus is incrediably hilly, and there are some hills where it is just more comfortable to run down. Would this thing have any effect on steep hills, I wonder?

    I don't know much about how the knee functions, but it seems like I do a lot more of this 'braking' in the last 50 ft of my trek to class than anywhere else

  • This weekend, the CBC radio program Quirks and Quarks had an interview with Dr. Max Donelan. You can listen to the interview in either ogg or mp3 format at http://www.cbc.ca/quirks/archives/07-08/feb09.html [www.cbc.ca]
  • to power an exoskeleton. The power source is right where you need it and you no longer have to carry those heavy batteries!!
    • Wouldn't the exoskeleton be useful in large part for supporting and actuating the legs (In order to carry a heavier load)? It would be like like hooking up a generator to an electric motor. At best you could recover some of the energy used for braking or slowing, but you would still need batteries.

      -b
  • to power the exoskeleton. Power is generated just where you need it, and you don't have to carry any big heavy batteries!
  • who would have thought that the six million dollar man could be the answer to the world's energy crisis?

    Do do do do do! Ba ba ba ba ba!
  • by ClarkMills (515300) * on Sunday February 10, 2008 @01:54PM (#22371660)
    The article with graphic:

        http://www.cbc.ca/quirks/archives/07-08/feb09.html [www.cbc.ca]

    The Interview (in OGG & MP3 formats) :

        http://www.cbc.ca/quirks/media/2007-2008/ogg/qq-2008-02-09_01.ogg [www.cbc.ca]
        http://www.cbc.ca/quirks/media/2007-2008/mp3/qq-2008-02-09_01.mp3 [www.cbc.ca]
  • Powering the device requires using calories you eat. However, every calorie you eat requires 10 calories of fossil fuel to get it in your mouth.

    As a consequence, whatever energy is used to power such a device needs to be measured against that yard stick.

    It's kind of like using an electric stove. One can (for example) burn natural gas to power a generator to power your stove, with, at best 20% efficiency (the nat gas turbine isn't super eficient, and then its dumped into electric lines that are lossy, an

    • by Stray7Xi (698337)

      Powering the device requires using calories you eat. However, every calorie you eat requires 10 calories of fossil fuel to get it in your mouth.
      That may be true for the average person. What if I grow my own food with no fossil fuels. Am I better off burning the food or eating the food and using tech like this? I guess that depends on what the food is. But this also has the side effect of extra exercise.
  • On a kids show called "Lets Get Inventin", Alex Drinkwater built exactly this device [tvnz.co.nz] - and got a full working prototype going.
    As you can see by the picture (half way down this article [idealog.co.nz]) direct image link [idealog.co.nz] the design is not only identical - it's BETTER with a built-in cellphone carrier! Somebody, give the kid his patent!
  • No one will buy into one of these if it isn't comfortable to wear.
  • by mdonelan (1236918) on Sunday February 10, 2008 @08:49PM (#22375082)
    Hello Slashdot community. My name is Max Donelan and I am one of the inventors of this energy harvesting technology. I thought I might try and clear up some of the misconceptions that people have about what we did. Here goes.

    When you walk, your muscles are constantly taking some of your mechanical energy away from your body and dissipating it as heat. Other muscles (or even the same muscles at a later time) are acting to put mechanical energy back in to the system. This is a little like stop-and-go driving. Perhaps more accurately, it is like driving with one foot on the gas and one foot on the brake. While walking this way may not sound like a good idea, it is what we do. We can take advantage of the fact that walking is inherently uneconomical to generate electricity economically. The idea is to use a generator to help the muscles in taking away the mechanical energy. But instead of dissipating it all as heat like muscles, the generator also produces some electricity.

    Here is a thought experiment that may make it a little clearer. If you stand up from your chair, your muscles that run down the front of your leg act to extend the knee. They increase your mechanical energy because by the time you are standing you have more gravitational potential energy. When you sit back down, the same muscles are active but now their job is to take the energy away from your body and dissipate it as heat (your kinetic energy is the same whether you are standing or sitting but your potential energy is less when you are sitting). Unlike traditional car brakes, your muscles require substantial "gas" (i.e. food) to decrease the energy of the system. And muscles are totally different than an electric motor - if you run an electric motor in reverse it takes mechanical energy and produces electric energy (i.e. a generator) but when you run muscles in reverse, they don't take mechanical energy and produce chocolate bars (i.e. food or chemical energy).

    OK, back to the thought experiment. If we were to couple a generator to your knee motion, it would always resist the motion. So, it would make it harder to stand up and easier to sit down. It would produce electricity in both directions. What if we had some way to engage and disengage the generator and we disengaged it when you are going from a sit to a stand and engaged it when you are going from a stand to a sit. While this would only produce electricity for half the time, it would actually make the whole task easier. You can get electricity and lower the effort required to do the task! Of course this requires you to already have the need to do the task and that is why it makes more sense to do it during walking.

    For the commenters that think it is too heavy, they are right. We are a year in to the next version and you can check it out on http://www.bionic-power.com/ [bionic-power.com] The graphic on the splash page will give you an idea of what it will look like. It will be less than 1 kg.

    With regards to other energy harvesting technologies, I think they are all pretty cool. My favorite is the self-winding watch. The drawback is that it gets only about 5 micro watts. The shoes are all very cool and will likely serve a real need but they also get much smaller amounts of power. If you are already carrying a heavy load, the backpack is fantastic.

    I am enjoying reading your comments so keep them coming!
  • What happens when you play DDR while wearing it?
  • It's a shame it generates electricity while walking. It'd probably be better if it zapped you because you weren't walking enough.

The greatest productive force is human selfishness. -- Robert Heinlein

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