Knee Brace Generates Electricity From Walking

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."

Does it double its output ...

by walking under heavy rain?

Re:Does it double its output ...

Only if its Chocolate Rain.

Lots of applications ...

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.

Considering the the potential energy stores in...

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. ).

Re:Considering the the potential energy stores in.

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.

Re:

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 the

Re:Considering the the potential energy stores in.

I wonder how long until they pair this with a water tight hydration recycling suit and we chase worms in the desert?

Re:Considering the the potential energy stores in.

Walmart shoppers can walk? Most I see park in handicapped and get around on tiny electric scooters.

Re:Considering the the potential energy stores in.

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!

less than one watt for one watt?

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

Re:less than one watt for one watt?

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.

Re:less than one watt for one watt?

Yes, you are right. This brace helps you to brake your leg, when you straighten it for next step. It uses your lower leg momentum to generate electricity.

Re:less than one watt for one watt?

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.

Well...

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 other news:

Knee Brace makes walking harder - Segway sees potential market opening

These stories are getting old.

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!

they had a bit about this on NPR

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.

You can get hurt by something like that

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.

There's an abundant source of power here

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!

Audio interview about the "Energy Brace" from CBC

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]

Comment by one of the inventors

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!

Re:Perpetuum mobile?

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....

Re:

Not exactly. The Maxwell demon takes what already is heat, these braces take what would turn to heat if unharvested.

Re:

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 eff

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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 th