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Motion As Power

lawrencerome.jpgDr. Lawrence Rome's "Suspended-Load Backpack" has clearly struck a nerve on the web, with links to it popping up all over the place. One aspect of the story that's unusual is that Rome is a biologist, not a product designer or engineer, and he published his discussion of the concept in Science. For Rome, the backpack is as relevant to the study of biomechanics as it is to figuring out new forms of energy production. I won't belabor you with the details of the backpack and how it works; National Geographic does a terrific job of filling that role. Instead, I'd like to speculate for a moment about the bigger picture.

We've become accustomed to idea of embedding solid-state electronics into various materials, making it possible for airplane wings to report otherwise invisible damage, walls to become solar panels, and objects of all sorts to be able to report their location and condition with cheap RFID tags. But all of these, while they may make the materials "smart" in some way, remain intrinsically passive systems. What happens when motion and pressure are added to the mix?

The Suspended Load Backpack, when thought of in the abstract, is an example of a system able to derive utility from otherwise wasted kinetic energy. It's not difficult to extrapolate from the backpack to other kinds of motion-based energy generation, such as the potential power in vehicle shock absorbers. This would be of some value to hybrid-electric cars. If the weight and motion of a backpack can generate seven watts of power, how much more could come from the weight and motion of a car? Would it match, or even exceed, the power input from solar panels?

And kinetic energy doesn't just mean power generation. Piezoelectric crystals turn physical pressure into electromagnetic output, and one might imagine that this is another way to make electricity. But as Dawn noted a few days ago in her piece on piezoelectric signaling, embedding piezoelectric crystals into the soles of shoes to generate energy from walking didn't actually produce much power (something mentioned by Rome in his Science article, in a comparison between the 20 milliwatt output of the shoes vs. the up-to-7.4 watt output of his backpack). Pressure into power wasn't much of a useful trick; instead, it turns out that the ability of piezoelectric crystals to turn pressure into electromagnetism is better as a method of sending short-range wireless signals. Dawn talks about one of the real-world applications of this process, a wireless light switch, but (again), what else can it do? Could we, for example, take advantage of this capability for environmental sensors?

Both the energy-generating backpack and the wireless, zero-energy light switch are very interesting and cool applications; both have the potential for widespread use. But for me, the greatest value they could have would be as harbingers of new technological families, or as catalysts for new ways of thinking about how we can best take advantage of our material surroundings. How else can motion and pressure be used to build a better environment?

Comments (6)

This invention is a tool. Like all tools it has a white and black use that should be examined. How dangerous is fire in an airplane's cargo hold? You can probably rig such systems to start a fire in transit. Parcel post, long distance transport, both are potential attack vectors.

I think that the thing is a neat invention and will end up being a net positive. That doesn't mean that we should be blind to the black uses. I'm tired of hearing "nobody could have predicted this". Yes we could.


Ok, I read the National Geographic article. It says nothing about the net energy gain.

Does your body have to produce more power when it carries the backpack than when it weren't carrying anything? Yes. So you just create more human power and convert it into electricity.

How is this different from an ordinary wind up generator (you know, the wind-up phones)? Or how is this better than electricity coming from a nuclear reactor, with which you reload your phone batteries? (Seriously).

In the abstract, isn't this a bad and inefficient way of producing power? It's going back to human power (a rather inefficient source for generating electricity - just compare it to the power you get from a gallon of gasoline in a combustion engine.)

I can see the benefits of such a backpack as a toy for gadget obsessed consumers - but not much else.

Maybe I'm missing something here.

Daniel Haran:

I'm not sure I see the point of this backpack, except as a cool hack / proof-of-concept.

Regenerative breaking, and watches that use movement have been around for a while. Hopefully this kind of zany application will provoke more people into brainstorming other applications. Unless that backpack gets 50 times lighter though, I'm not about to be carrying one to power my gadgets any time soon.

Jamais Cascio:

For what it's worth, I don't believe that the backpack is intended for people just casually hauling their cellphones and iPods around. Instead, the design is meant for people who normally would (a) be away from grid power for an extended period, so (b) have to carry extra batteries for their gear, and (c) end up carrying backpacks for other supplies, too. That is, soldiers, aid workers, researchers in the field, and the like.


What's new about that?
Usage of humans as the power cells like in Matrix

the mindtaker:

The article states that the backpack weighs only a few grams more than a comparably sized frame pack. So first of all, if you're already carrying around enough gadgets to warrant a backback, there's no net loss in energy spent wearing the fancy-pack, and additionally, the more things you keep in your backback, the more energy would be lost (in a normal backpack) due to having to compensate additionally for greater force tangential to the ground (durr, gravity -- it's why the people's hip movements shallowed out also...)
In other words, this device is syphoning energy from one side of a force reaction. You initially have to apply energy to beat gravity and move upward in order to take a step. When your extended foot comes back down, you have to apply equivalent upward force to negate the additional potential energy of your backpack now falling from a slightly greater hight. This backpack, like any hybred car, syphons energy that would otherwise be wasted as heat and vibration as compensation occurred. That's also why it's more comfortable. It's just as hard to step upwards when you wearing either pack, but on the way down, the pack is exactly like a shock absorber, but instead of dissapating the energy as a simple absorber would do, it takes the additional step of converting it into more useful forms of power. Jeeze people, it's not super new, but it's not nearly as blurry as the view you have 3 inches from your noses.


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