Potenco was always a battery charger, so please tone down the faux surprise.

Well, the ergonomics suck. The pull handle is too small and poorly-shaped to use two hands which doesn't matter since it's designed to be held in one hand and pulled with the other. That negates a rowing motion which is a good way to get a reasonable amount of power out of a human being for a reasonable length of time.

Bicycle's the other way to get power out of a human being but it requires a more complex mechanical setup. You need foot pedals a seat and somewhere to attach the generator. To use the rowing motion all you need is loops for your feet and a generous handle for your hands. A return spring would help but isn't necessary. After all, row boats don't have return springs.

The other thing that struck me right away was the string. If that's the string that goes out with the finished product it'll last a day or two. It ought to be substantially thicker and the attachments ought to simple requiring no specialized end fittings and capable of operation with a wide array of improvised strings.

One of the slides said "20 watts" output which seems a bit on the high side. I wonder if that's peak output or a sustainable output?

Finally, I wonder what the Freebird people are up to? The OLPC seems like a natural fit for them. It would have been nice to make the XO "all in one" but the idea of a spring-loaded cranked generator is still appealing. Anyone know how their product line is faring?

allen,
I do not quite agree on the string thickness. If they use a modern high performance fiber like dyneema or similar the string can be kept very thin and still have an enourmous tensile strength. And thin strings last longer when pulled around an edge. Thicker strings would need small wheels instead of an edge.

I agree that both ends should have universal attachment points such that it can be fixed to your feet or a table leg or you could tie a stick to the free end of the string for using both hands e.g. for a rowing motion.

I'll take your word for the qualities of dyneema since I'm not familiar with the stuff. Maybe it is up to the job but it's also the part of the generator that's going to take the greatest beating. It'll get dust and sand on it, it'll get wet, it'll be used by people who'll think pulling harder is pulling better.

If it's strong enough to handle all that it may be that it's too strong. Which would you rather have break, the pull string or the pull string attachment? String's replaceable but if the attachment breaks you're probably screwed. In the U.S. that's no big deal but in some dusty farming village ten miles away from the nearest road when the battery goes flat you're done constructing knowledge.

allen,
nothing is indestroyable. If a cow stomps on an XO you're done also :-)
If you expect the users to take care of an XO they might use the same care for the yo-yo. So I think it only has to be designed for normal useage with some contingency and not for abuse with herculian forces.

I've had a lifetime of modest DIY electrical generation, based around bike dynamos,wind genes, solar PV & even early 1900s telephone hand cranks (still working!).The early claims of 20W for the Potenco IMHO just did not stack up,as the video above finally verifies. Yikes-claimed XO/OLPC 3-5W running power was not even met by this string puller!

Most humans just can NOT deliver 20W by hand for more than a few minutes anyway- we're typically limited to a few Watts at best.The ergonomics of hand genes, especially in confined spaces,are never good of course either. Us humans have more valuable things to do with our hands as well,ESPECIALLY when alone at a computer keyboard,or holding a pen or drink!

Instead consider foot cranks, much as once used 1929- by Australian Flying Doctor/School of the Air/Lighthouse valve pedal radio transmitters. Our feet are idle when seated of course, & are FAR MORE "POWERFUL" & fatigue resistant than hands. See => http://www.lighthouse.net.au/liGhTS/Bulletin/0003/Solitary%20Island%20Pedal%20Radio%20br%203.jpg

With long life LED lighting & cell phones now abounding,exhaustive studies on energy scavenging have begun recently(=>Google),with foot power again identified as good for a near effortless few Watts. Far more appealing however was the use of cheap/no moving parts solar PVs, which now typically retail at just US$5-10 a Watt. Given the abundant solar resource in the OLPC target markets,it begs the question as to why such simple PVs aren't considered the best charging approach...

So if a country decides to sign up for oplc, not only will its citizens get computers for eduction, communication, internet connection, and so on, but also an electricity source for uses such as lighting and cell phones.

This is yet another way oplc is a remarkable economic development investment, and hence yet another reason that countries are likely to take it up.

As you can see in the Negroponte video, the Potenco yo-yo comes with a black velcro strap, to fix it to the wall and pull away from it, thus using less energy than holding the yo-yo with the other hand.

The video was hardly a demonstration of the string charger - it was mostly Nick and his Peruvian prospective client posing for pictures with the XO, and taking a few perfunctory pulls at the yo-yo. I was amazed when Nick mentioned running the XO without the battery - he's clearly a "big-picture kind of guy".

And of course, it didn't work because something was wrong with the hardware - hardly anything that the head of the project should concern himself with (the line usually taken when the demo fails).

Eventually someone will ask Nick to actually charge up a battery - right then and there, and without excuses. I want to see the video of that.

They've got a ways left to go on that yo-yo. Dirt will be a major factor in the string lifetime, and they'll have to test in real-life conditions.

For Charbax's benefit - fastening the string to a fixed object does not relieve you of half the load. In fact, it doubles the load to whatever arm you're pulling with (for the same output).

The generator needs to be designed to use rowing and pedaling motions (the Ecosystems Nepal twin-tripod generator would be a good start, given a sliding seat and handholds in the right position). That way you could use an entire group of arm and leg muscles with every stroke. I fatigued the handlebars off of a bicycle that way in my early college years.

Ecosystems Nepal developed a village gang charger for LED lighting based on a cheap lead-acid battery. It was clearly a systems problem and they had to solve every aspect, from the connectors used to the wood housings for the batteries to the electronics in the housings that rpevented excess discharge.

The yo-yo is not just a generator fro the XO. People in rural villages are clever and know how to make use of whatever resources they have. Give them the yo-yo and the XOs and they will work up some very unique uses which may or may not solve their problems, but they will try. The hardware has to be designed to survive such use.

Roland, I know nothing is indestructible but design decisions can drastically effect the utility of a device. Poor design makes a device more difficult to use then it needs to be and less reliable then it should be.

In the case of the yo-yo generator it's the line that's most vulnerable. The generator can be sealed pretty effectively but the line is out there without any protection. It *will* break no matter what it's made of so the design should take that into account by making replacement of the string by some local expedient easy, not difficult.

As someone up the thread pointed out, the yo-yo generator won't be used exclusively by kids to charge their XOs. A reliable, or any, source of electricity is problematical in the areas of the world targeted by the XO so any reliable source of electricity is going to be pressed into service powering any electricity-using device that can be adapted. It's going to be used a lot so it had better be both reliable and maintainable otherwise it won't last very long.

It is obvious (pretty sure also to Potenco) that you can generate more power with your legs than with your arms.

But to use leg power you need a bulky structure like a bicycle on a stand or a seat on legs with foot cranks integrated (Nepalese solution) or a rowing mechanism with sliding seat. All those solutions will be expensive, bulky, heavy and therefore not mobile.

A foot pedal for pumping motions will only work when standing. A foot pedal such as used with old sewing machines will probably be impractical either because you would require a table and a chair. But you should be aware that in many places in Africa furniture like tables and chairs are not commonly used. Not simply because of poverty but it is not part of the local culture. Almost everything we would do on a table they do on the floor. So you should not expect kids using their XO at home at a table sitting on a chair. Most likely the kids will sit on the floor. And in this position it is hard to use your legs efficiently. Either you would have to interrupt computing and stand up for charging with a foot pump or you would have to use an arm driven device with all its disadvantages described above.

Probably Potenco decided for the compromise of using the floor sitting arm driven solution.

To use a "rowing" action all you need is a handle big enough to comfortably grasp with both hands and some solid to fasten the generator to. Then you sit on the floor and start rowing. A sliding seat makes it more efficient but it isn't necessary.

David Butcher's highly educational PPPM (Personal Pedal Powered Machine) => http://www.los-gatos.ca.us/davidbu/pedgen.html#Latest_News is surely the way to go !? He quotes 50W-80W is a breeze, & has even driven an electric chain saw directly off one. Any one had PPPM experiences?

It's a pretty cool gadget but it's overkill for the OLPC. I could see it being used to gang-charge twenty or more OLPCs but as part of the standard kit it's unnecessary.

Agreed ! Although extemely educational his bike gene is certainly a single XO charger overkill, but then the string Yo-Yo increasingly looks a serious UNDER-kill. IMHO a 5-10W PV is surely the obvious single XO charger.

Incidentally,here in New Zealand rescued Fisher & Paykel "Smart Drive" electronic washing machine brushless motors are EXTREMELY highly thought of for DIY genes, with serious hand, hydro & wind applications abounding. Check the hand cranked one shown => www.manuka.orcon.net.nz/smart.jpg that's good for 50W.

Even if it is 20W average (I don't know about that by hand, though I can easily do 300W for extended periods on a bike, peaking at 600W), it is entirely possible that the power is going to zero at the end of each pull, thereby killing the laptop.

If the laptop or generator itself had a super capacitor, this could be smoothed out to easily power the laptop.

BTW: I think it would be best to fix the gen to a high point, then pull down like a water pump. Also, it would be good to make the generator adaptable, so you could, say, pull the case off and use and alan-wrench to replace the string spindle with, say, a sturdy hex-socket that you could drive with a bike.

James- you must be an Olympic athlete in training,as "300 W for extended periods" is universally considered WELL beyond what most humans can produce for more than ~30 seconds. Even the legendary Dave Butcher only averages 150 W output bursts when "in shape". See => http://www.los-gatos.ca.us/davidbu/pedgen.html

Such a ~½ HP output as yours implies you could run up numerous flights of stairs without gasping or hitting lactic acid issues.Can you?

Many children,even the fit sports mad,find ~50W their extended limit on exercycle style generators I've found here in NZ.

Hi,
Where can I buy two of these YoYo chargers?

The spec sheet is here: http://web.archive.org/web/20070422024256/www.potenco.com/files/Potenco_OLPC_Spec_Sheet.pdf