As the One Laptop per Child project, a nonprofit effort based in Cambridge, MA, nears the completion of its rugged and versatile laptop designed for school children in poor countries, a key component has fallen into place: an efficient, human-powered generator that could make the computer practical for children living in areas without reliable, affordable electricity.

The new generators, which will be field-tested beginning this October, abandon the bulky and inefficient hand-crank design featured on an early mock-up of the laptop in favor of a more compact off-laptop design that uses a pull string to spin a small generator. It was developed by Squid Labs, Emeryville, CA, a design and engineering group whose co-founders include several graduates of MIT’s Media Lab, where the laptop project originated.

The $100 dollar laptop will include a 7.5-inch screen, a 500 megahertz processor, 500 megabytes of Flash memory, and wireless broadband for forming impromptu networks with other laptops. It will also be a multimedia workstation, supporting the playing and composing of music, for example.

The new generator will make the laptop much easier to power than it would be with a hand crank, in part, because the users will be able to operate the generator in a variety of ways, including holding the device (the size of two hockey pucks) in one hand and pulling the string with the other, or clamping the generator to a desk, attaching the string to one foot, and using leg power. “We wanted something that could take advantage of other muscle groups in the human body that can put out a lot more energy than the muscles that you get when you’re just turning a crank,” says Colin Bulthaup, a co-founder of Squid Labs.

To reach the project’s goal of one minute of power generation for every ten minutes of laptop use, the generator would need to produce 20 watts (the laptop will require less than two watts in a primary application as an electronic textbook replacement). “With a hand-crank system, if you’re gung-ho about it, you can get about five watts out of it. But you get tired after about a minute or so,” says Geo Homsy, a partner and designer at Squid Labs. With the new system, generating 20 watts is comfortable, and it’s possible to generate 10 watts for “as long as you want,” the developers say.

The new generator is also quiet – one of the key design requirements. “If you imagine an entire school room full of kids using this thing, it needs to be as quiet as possible. Otherwise it will drive everyone insane,” Homsy says. Typical generators work best at high revolutions per minute, requiring noisy gears to step up the speed. The developers have done away with gears by custom-designing a generator that runs most efficiently at lower RPMs, a move that also makes possible a smaller device.

To customize the generator for children with varying strengths, or so that users can decide how hard they want to work, the design includes a computer chip that continuously adapts to how much resistance users feel. This electronic “variable motor loading” is like changing gears on a bicycle to go up a hill, Bulthaup says. “Each person pedals at the same speed, but a stronger person can push harder with each stroke. Our device automatically adjusts the loading to reach that optimum comfort/power point.”

The device meets other key criteria, too, including durability and ease of use. If the string breaks, for instance, it can be easily replaced with a shoe string, or a similar object. And the generators should cost less than $10 apiece, Bulthaup says.

In an e-mail, Nicholas Negroponte, chairman of the One Laptop per Child project, says the device is the best-performing of the many they’ve looked at so far, and that they intend to use the design with their laptops – if it continues to perform well in tests and another, better design does not appear. Other human-power options may also be used, however, depending on the situation, says Mark Foster, the project’s vice president of engineering and chief architect.

The $100 laptop developers are also working with several firms on an ambitious, related project: developing a long-lasting battery system to be paired with the generator (or to charge off AC power). This battery system will include “custom chemistry, unique electronics, and complex charge and discharge monitoring algorithms to deliver 2,000 battery cycles – four times more than normal PCs,” Foster says. A long charging session in the morning, for instance, would allow kids to use the laptop throughout the day, with the batteries storing enough energy for eight hours of work – with enough left over for the computer to serve as a wireless mesh network router for another 16 hours.

The $100 laptop, which the developers expect to start shipping to interested countries next year, will actually cost $135 to manufacture at first, before it drops to a projected $100 by 2008.

The project is making steady progress, moving forward on its integrated circuit, software, and industrial designs, Foster says. Once everything is ready, the group plans to conduct extensive testing: they’ve set aside 500 laptops to be tested until they’re destroyed – to make sure they’re rugged enough for rough environments.