Knee Brace Generates Electricity From Walking 128
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."
Considering the the potential energy stores in... (Score:4, Interesting)
Re:Considering the the potential energy stores in. (Score:3, Interesting)
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 appreciation or something
A lot of the antismoking stats seem to assume that nonsmokers never die. Worse - some even use the potential lost future earnings of a smoker who dies early as a "cost", which is _bullshit_. Smokers dying early means you don't need to support them later. Unless they are dying so early ( <25 ) when they haven't yet fully paid for the cost of bringing them up etc.
Maybe a smoker dying at 40 or 50, from lung cancer might be expensive. But dying from some other cancer is quite expensive too, and if the "nanny state" country has to take care of them from 60 till 80 when they finally die it gets more expensive.
As for obesity. IMO dying from a heart attack isn't that bad a way to go. But diabetes is.
Re:Considering the the potential energy stores in. (Score:5, Interesting)
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!
Comment by one of the inventors (Score:5, Interesting)
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!