Bounce Your Load and Get Charged Up

December 8, 2005 8:49 AM

Be. The. Battery.
A brilliantly simple concept will allow anyone who needs (a small amount of) power to generate their own just by walking around while wearing this special backpack. By mounting the pack's load on springs connected to a rack and pinion device that is, in turn, connected to a small generator, the wearer's natural walking motion can generate up to 7.4 watts of power. Plenty enough to keep your Nofriendo DS charged. Or your sniper rifle's night scope.

The bonus? By having the pack's load on springs, the backpack is more comfortable and ergonomic than a traditional backpack too.
posted by fenriq (40 comments total)

I imagine that the ergonomic benefits would be lost the moment you break into a jog.
posted by eddydamascene at 9:06 AM on December 8, 2005

See, I've told my fellow hikers this would be a good idea for years. Those jerkbags just laughed. Guess who's laughing now!
posted by Plutor at 9:13 AM on December 8, 2005

I would imagine it's actually quite a bit less comfortable and ergonomic; you want a heavy pack close to your body and not moving.

The power is coming from somewhere; in this case, it's additional work done by the person carrying the bag. I suppose the premise is that food is more calorie (energy) dense than additional batteries. Still, I'd think additional fatigue while carrying an already heavy load (80+ pounds is pretty obscene) would be a bad thing.
posted by JMOZ at 9:15 AM on December 8, 2005

Mmm... a good idea. But is it durable? If you drop it, or break a leg and fall on it, will it remain intact?
posted by malusmoriendumest at 9:15 AM on December 8, 2005

that's a good point eddydamascene, you might be able to time things right on an even flat surface, but taking any kind of alternate terrain at a good clip seems likely to throw the steps and springs off sync. As well it would seem to be a potential impediment to solders in situations where they have to do a large amount of sudden quick movements.

I was wondering how heavy this thing must be... the article didn't specifically say (I don't think), there was something about the load plate being able to support 84 lbs, but if I read correctly that was in addition to the system itself?

seems like it'd be bugger heavy, even with springs.

Metafilter: even with springs
(srry)
posted by edgeways at 9:17 AM on December 8, 2005

Jeez, that looks like it'd be the most awkward and uncomfortable thing ever invented.

I'll believe it when I hear from someone who could prove they weren't a paid shill.
posted by HTuttle at 9:24 AM on December 8, 2005

Presumably they could add some sort of easy locking mechanism that would keep the pack secured if you needed to run.
posted by oddman at 9:24 AM on December 8, 2005

I'm sure there are other issues that are being dealt with but the underlying concept is pretty damned cool. Who hasn't wanted a little juice while in the backcountry?

They tested it with loads between 44 and 84 pounds. A 44 pound pack is reasonable while an 84 pound pack is torture. There wasn't any mention of how much extra weight the system added.

Plutor, they laughed at me too. I might just email them the article with a single word, "Ha!".

malusmoriendumest, I'm guessing the final version will have to be pretty tough if the military is considering adopting it for field use.
posted by fenriq at 9:34 AM on December 8, 2005

Who hasn't wanted a little juice while in the backcountry?

Oo-err, missus. There's nothing I'd like better than a little juice in the backcountry.
posted by PeterMcDermott at 9:39 AM on December 8, 2005

The article says the pack frame is 5 lbs. Add maybe 2 lbs. for the nylon bag and straps and you have a fairly heavy pack as these things go. But yeah, some extra juice in the backcountry would be cool. Has anyone had any experience with backpacks with solar panels attached, like these?

(Also at Popsci.com: The Linux-Powered Keg Fridge.)
posted by LarryC at 9:41 AM on December 8, 2005

I'm sure there are other issues that are being dealt with but the underlying concept is pretty damned cool.

It's very cool and one I've been thinking about for a while. This backpack is a good start but, I think so much electricity (and jobs/ new technology) could be generated by passively harnessing people's daily activities. Imagine installing electrical generators on the turnstiles at a place like Grand Central Station in NYC. (If you've never been there during rush hour, It is basically a mighty non stop river of human energy flowing through it). You could power a whole building with it. It would need to be perfected so as to develop a highly efficent manner of energy collection and storage, but it could be huge, given the proper commitment.
posted by Skygazer at 10:06 AM on December 8, 2005

It seems like we'd be better off harnessing the locomotive powers of the legs through fancy shoes, but I'm talking out of my ass.

For this kind of backpack to be efficient, it seems like it *needs* to be really heavy.

I live for "extra juice in the backcountry."
posted by mrgrimm at 10:12 AM on December 8, 2005

The person who invented this is a professor of physiology in the very department I work in at the University of Pennsylvania!

Much of the media attention to Larry Rome's device came about two months ago. The original paper in Science is located here.

Research on the backpack was orginally funded by a grant from the US Navy, if I remember correctly.

The military application is obvious, since soldiers in the field have to carry a lot of electronic equipment that requires power (computers and communication devices, particularly). The more equipment, or the longer the mission, the larger the capacity (and the heavier the weight) of batteries are required. Solar power and other approaches are not as efficient or are condition-dependent.

As explained to me by Dr. Rome, walking is a highly mechanically efficient process, and the act of adding the weight of this power generation device to a backpack does not consume much more energy than the carrier is already expending to begin with, giving an efficient return and a ready source of energy in the field.

This backpack design was a bit of a lark; normally Larry works on the contraction of frog hind-leg muscle.
posted by Rothko at 10:14 AM on December 8, 2005

solar+batteries would be lighter IMO for the average backer. This looks like somthing a member of a special forces squad wears to power a sat-link while on extended patrol.
posted by stbalbach at 10:15 AM on December 8, 2005

The good news: This device may some day so drastically cut the military's reliance on oil that the soldier wearing it may not need to be there in the first place.
posted by weapons-grade pandemonium at 10:16 AM on December 8, 2005

oops thanks Rothko for the more detailed explanation -- but it seems like the added weight must be a factor, how much added weight and space is it?
posted by stbalbach at 10:17 AM on December 8, 2005

weapons-grade pandemonium, now THAT would be something, wouldn't it?

Rothko, thanks for the additional info about Dr. Rome. From the Pop Sci article it was apparent that he's a very interesting character who would have been a great teacher to have, I think. I always loved the teachers who taught out of a passion for knowledge and their love and sharing it. And I knew this was a couple of months old, I did alot of searching to make sure it hadn't been posted before. Even opening up a can of MeTa!

skygazer, it seems to me that there are so many ways and places that energy that's just being lost could be captured and re-used. Stairs, turnstiles, highways (I remember a PopSci article about a fan system that was driven by cars passing on each side of an island on the highway) and heck, even sidewalks.
posted by fenriq at 10:28 AM on December 8, 2005

About efficiency:

Finally, despite the smaller than predicted ∂metabolic power input, individuals may have to carry extra food in order to power electricity generation. This weight, however, is negligible compared to the weight of batteries required to generate the same electrical energy. The specific energy of food (3.9x10⁷ J kg^-1) (22) is about 100-fold greater than the specific energy of lithium batteries (4.1x10⁵ J kg^-1) (1) and 35-fold greater than that of zinc-air batteries (1.1x10⁶ J kg^-1). Given that the "metabolic efficiency of electricity generation" (electricity power output/∂metabolic power input) is 19.5% (table S3), the extra food to be used for generating electricity would require about 20- and 6.8-fold less weight than lithium and
zinc-air batteries, respectively (23).

About why the load needs to be heavy, and mechanically detached:

A considerable amount of mechanical energy must be transferred (or generated de novo by the muscles) if the load is heavy. In the case of a 36-kg load, 18 J of mechanical energy transfer (or work) accompanies each step (assuming 5 cm displacement), and at two steps s^-1, this is equivalent to 35 W. Although this represents a large potential source of mechanical energy, it is also inaccessible if the load is rigidly attached to the body.

Which is to note that the added weight of the design is negligible compared to the fact that the overall weight is what drives the energy harvest.
posted by Rothko at 10:41 AM on December 8, 2005

My response to when I'd first heard of this idea was along the line of JMOZ: not only more comfortable, but more tiring as well. A seasoned hiker knows that you don't want anything loose or jostling on your pack precisely because the momentum that this device utilizes is both tiring and destabilizing. Woe be the soldier or hiker going down a steep mud embankment whilst their power-generating pack goes "pushy pushy" with every step.

The image that immediately comes to mind is that this would be much the same as having your sleeping bag strapped to your frame on bungees -- something I've seen more than my share of times leading first-year summer campers on overnights.

That energy ain't free, y'all. Better to go solar. Its here now and adds no ergs. Better yet, get standard battery-opped technology. Also solar-rechargable and available in most corner stores worldwide. More weight? Yes, but less tiring than endless jostling.

I mean, how much electronic crap do you need to bring into the wilderness anyway? A camera, maybe a lamp. Certainly not a generator's worth (soldiers be damned).
posted by Ogre Lawless at 10:43 AM on December 8, 2005

s/more comfortable/less comfortable/.
posted by Ogre Lawless at 10:43 AM on December 8, 2005

Nay-sayers, it's a prototype, cut it some slack.

That said, I'm holding out for generators in my bootheels.
posted by lodurr at 10:46 AM on December 8, 2005

Six male participants walked at speeds ranging from of 4.0 to 6.4 km hour^-1 (2.5 to 4.0 mph) while carrying 20-, 29-, and 38-kg loads in addition to the fixed portion of the instrumented pack frame, which weighed 5.6 kg (12).
posted by Rothko at 10:47 AM on December 8, 2005

That said, I'm holding out for generators in my bootheels.

Already been done:

Therefore, researchers in the field have focused on putting devices in the only accessible location: the shoe. Such "heel-strike" devices, however, have permitted only small levels of electrical energy generation (10 to 20 mW) (2, 6). The primary reason for this limitation is that on a hard surface, essentially no mechanical work (force times distance) is done at the foot/ground contact point, because under normal circumstances the point of vertical force application does not move in the vertical plane (that is, distance= ~0).

Although one can make the shoe compliant so that the foot moves a small distance because of compression of the sole and heel (7), this is problematic because increasing compliance leads to declining maneuverability and stability. Although considerable effort has gone into developing exotic energy-generating technologies for shoe devices (8), the small magnitude of the mechanical energy source remains a
limitation.
posted by Rothko at 10:49 AM on December 8, 2005

7.4 watts of power extracted from a human being that
is going to be walking all day (like a backpacker), is
7.4 percent of their power output (a human is good
for about 100 watts of power, all day long).

You would certainly feel the drain. Nothing on my
backpacks flops or swings. And what do you need that energy
for? 50 watt hours a day? That's 50 AA NIMH batteries a day!

I can see this for a soldier, but for a civilian, get something
like this.
posted by the Real Dan at 11:11 AM on December 8, 2005

I applaud all alternative energy generation and any progress on that road. I love that the battery pack weighs almost as much as a full kit does already. Let's hope this gets miniaturized handily.
posted by Busithoth at 11:11 AM on December 8, 2005

Fenriq: Stairs, turnstiles, highways (I remember a PopSci article about a fan system that was driven by cars passing on each side of an island on the highway) and heck, even sidewalks.

Yeah the possibilities are endless once you stop and think about it. It could be the gateway to a whole new source of energy and reduced reliance on a certain troubled area of the world. ;-). If the oil companies even spent a small percentage of their profits on alternative energy technologies, the mind boggles, but why would they want to shut off any profits whatsoever from a source that has an expiration date and is f--king up the planet and this country. This is the place where government should step in and contain the short sightedness of hypercapitalism (absolute power corrupts absolutely in all political systems, not just Communism and Fascism) , but alas I digress...

I think down the road the success of this sort of passive power generation/collection lies in some sort of supersensitive revolutionary piezoelectrical-like technology that doesn't hinder or influence motion (by reducing stability/maneuverability/energy level etc..).

Turnstiles. If someone would test just one turnstile in Grand Central for one month...
posted by Skygazer at 11:51 AM on December 8, 2005

Many a time I've been working out in a gym with ten to thirty other people all chugging away on exercise machines, and wondered what kind of an impact we could have on the Y's energy bill if that output were harnessed....

You could design resistence trainign equipment to scavenge power, too, though getting precise resistences would be a challenge, I expect. And while you're at it, install baffles in the pool to scavenge the energy from passing swimmers....

The potential for gain by combining conservation and small-generation is great; if you incorporated light concentrators and light pipes into building designs, you could reduce daytime energy use by a significant amount. We still need to have ways of pushing the energy into a local grid, though.
posted by lodurr at 12:19 PM on December 8, 2005

AP story (from September).

"Metabolically speaking, we've found this to be much cheaper than we anticipated. The energy you exert could be offset by carrying an extra snack, which is nothing compared to weight of extra batteries," Rome said. "Pound for pound, food contains about 100-fold more energy than batteries."
posted by russilwvong at 12:25 PM on December 8, 2005

Lodurr: Many a time I've been working out in a gym with ten to thirty other people all chugging away on exercise machines, and wondered what kind of an impact we could have on the Y's energy bill if that output were harnessed...
Right and energy producers could get a break on their energy bills (and high tech batteries for their electric cars) or a discount on public transportation. Old folks would get a break on everything just for all the energy they've produced their whole lives.

A lot of overweight folks in this country would hit the gym and droop that dangerous fast food tonnage if they knew they'd get a break on their energy bills. ;-)
posted by Skygazer at 12:59 PM on December 8, 2005

Many a time I've been working out in a gym with ten to thirty other people all chugging away on exercise machines, and wondered what kind of an impact we could have on the Y's energy bill if that output were harnessed....

Cue the Upright Citizens Brigade...
posted by Rothko at 1:34 PM on December 8, 2005

When you're hiking you don't want things flopping around haphazardly, that's true. But you still use energy to lift up unsprung weight as you start a step (I assume you're raising the pack's center of gravity when you step or else this pack wouldn't work.) And you don't get that energy back when you complete the step; if anything your upper quads have to work harder to decelerate the extra weight.

It seems to me that flopping loads cause balance problems because of period mismatch; their COG goes up and down faster than the hiker's pace. Presumably the inventor designed this pack to keep the load at more or less the same height though the full cycle of a level step -- you can do this if you know the load's weight and hiker's pace by tuning the springs -- and therefore the energy you'd use to lift the load unnecessarily instead goes into the generator.

Also, as you complete one step and start a new one the dynamic force on your foot should be less as the load's downward velocity is reduced. That isn't the case with most uncontrolled flopping loads.

So yes, the juice has to come from somewhere, but I suspect a lot of it comes from energy that the hiker would otherwise waste. Also there could be some benefit to the quads and soles, especially on steady downhills. Hopefully there's a way to lock the load for tricky climbs and descents; in those cases you'd be out of the favorable period regime and having your load on springs could make things worse.

Disclaimer: I am not an engineer, just a bored hiker on the Internet.
posted by Opposite George at 1:37 PM on December 8, 2005

mmmmm ... strap one on, grab a motorized love toy and optionally your significant other and voila ... perpetutal emotion.
posted by boofhead at 2:52 PM on December 8, 2005

What's with the jab at Nintendo?
posted by nightchrome at 4:53 PM on December 8, 2005

nightchrome, did I misspell it? Oops, I guess I did. No jab intended, that's what my friends and I have always called 'em. Nofriendo, Praystation, HexBox, we're a regular laugh riot.

But I've gotta say, I like boofhead's thinking.
posted by fenriq at 5:07 PM on December 8, 2005

Actually, capturing this energy could be less tiring if you're jogging. A bit like a hybrid car.

I was jogging while carrying stuff the other day, and it is far less work to jog if the weight is free to stay put, than it is if, with every step you have to overcome its inertia and reverse it's direction (up down up down).

The gains in the inertialess mechanism may outstrip the costs in sucking some of those gains back out.
posted by -harlequin- at 6:17 PM on December 8, 2005

Actually, let me strengthen that to the gains can outstrip the costs and result in a less tiring run, because the gains are significant, and you just put a smaller generator in there that extracts less power until the amount you are taking out is less than the gains, resulting in a slimmer, but net gain in ease of movement.
posted by -harlequin- at 6:19 PM on December 8, 2005

About the small-power generation ideas, like turnstiles. I don't want to be Grumpy Gus here, but before anyone gets excited about this, you do have to consider the energy-cost of harnessing that power.

Like, take a turnstile. If one person turning a turnstile once produces 1 unit of power, and your turnstile generator has an expected lifetime of one thousand turns before it wears out and requires replacement, then it doesn't work unless your turnstile generators each cost less than one thousand units of power to produce. And then you also have to consider all the mechanics of sending those little bits of power back into the grid. If your turnstile produces one hundred energy units per day, but a repair costs two hundred thousand units, you might very well be better off just forgetting about it entirely.

I'm not saying none of it could work, just that before you sink a chunk of NY transit money into this, someone's gotta develop the device and figure out the numbers to demonstrate that it actually produces more power than it costs. The track record for micro-power ideas is that when you do figure it out, they turn out to be unfeasable in this way. The stuff we mainly use for power (oil, nuclear, coal, hydro, etc) gets used because it produces enormously more power than it costs to exploit.

If we could efficiently capture a lot of these little sources of wasted energy, that would be great. But in the world of grime and friction, there's always a cost, so there's a physical floor to what's practical to exploit and what isn't. Even if there's a potentially vast amount of total waste in some routine activity, capturing and using it can be like pumping oil by hand with a teaspoon.
posted by rusty at 8:37 PM on December 8, 2005

rusty, you are right, for now. But that's the best part of science and technology, what's possible and feasible (explicitly noted as not the same thing) today aren't necessarily going to be impossible or unfeasible tomorrow.
posted by fenriq at 9:57 PM on December 8, 2005

Rothko: Cue the Upright Citizens Brigade...

I should think the Recumbent Citizens Brigade would be more efficient....

rusty: .... before anyone gets excited about this, you do have to consider the energy-cost of harnessing that power.

.... And then you also have to consider all the mechanics of sending those little bits of power back into the grid. If your turnstile produces one hundred energy units per day, but a repair costs two hundred thousand units, you might very well be better off just forgetting about it entirely.

.... Even if there's a potentially vast amount of total waste in some routine activity, capturing and using it can be like pumping oil by hand with a teaspoon.

Well, what fenriq said, but I'll add: Yes, this requires a change in design at a very basic level. We need to shift to lower voltage electronics (and that includes power electronics), and need to start thinking in terms of microgrids rather than of "the grid". For a long time, energy have been very cheap -- so cheap, that your payoff equations have meant we could rely on some relatively inefficient electrical devices.

The advent of commercial and consumer hybrids is a big step in this direction. Not so much because of the added savings in energy, as because it entails an increase in R&D efforts.

Another thing that would have a huge impact would be to look at ways of powering your own devices. Can a person generate enough electricity to power a mobile phone (or its next generation equivalent). Scavenging linear motion to power a rotary generator is one way; I can remember reading about research on using piezoelectrics in shoes...ok, here is it [pdf]: Parasitic Power Harvesting in Shoes, by a bunch of guys at the Physics and Media Group at MIT. (Isn't that the anti-Media Lab group?) They notes some significant problems, mostly related to the 'impact on gait'.

Finally, Mark Twain has something to say on this as well (via Technovelgy):

His stand was a pillar sixty feet high, with a broad platform on the top of it. He was doing what he had been doing every day for twenty years up there - bowing his body ceaselessly and rapidly almost to his feet. It was his way of praying. I timed him with a stopwatch, and he made twelve hundred and forty-four revolutions in twenty-four minutes and forty-six seconds. It seemed a pity to have all this power going to waste. It was one of the most useful motions in mechanics, the pedal movement; so I made a note in my memorandum book, purposing some day to apply a system of elastic cords to him and run a sewing machine with it. I afterward carried out that scheme, and got five years' good service out of him; in which time he turned out upwards of eighteen thousand first-rate tow-linen shirts, which was ten a day. I worked him Sundays and all; he was going Sundays as well as weekdays, and it was no use to waste the power...
[Connecticut Yankee In King Arthur's Court]

posted by lodurr at 3:37 AM on December 9, 2005

Lodurr kudos for the Twain quote. No thread is complete without that wonderful man's words.

Like I was saying above, I think a revolution is just about here on the development of microelectronics and piezoelectric technology of an order analogous exponentially to the difference in energy generation between conventional explosives and nuclear weapons.

Rusty: You are correct, of course. The cost effectiveness at present is like in serious negative space, but we have to begin somewhere and even if it captured the imagination of the country, leading to something like a Space program in the development of this technology, I'm not sure how that could be measured in monetary terms. It would change our lives so much for the better (if the Oil companies don't do everything in their power to suppress it and throw proponents of it into Neocon gulags).

I'm gratified that those kooky kids at MIT are already on the Piezoelectric tip sussing out the details (details..details..). I was unaware of that study. In the meanwhile if anyone needs an idea or to have their socio-technological tea leaves read send me a nickel and a good joke and I'll see what I can dig up.
posted by Skygazer at 2:36 PM on December 9, 2005