This is a project I've been working on for some time. My students typically spend most of the library time sitting at our computers. I thought perhaps they could be burning a few calories at the same time by riding a recumbent stationary bike. I purchased an inexpensive one, and it was an immediate hit. It also occurred to me that, with a little bit of ingenuity, all that energy they were expending turning the cranks might be put to use creating electricity.

After much trial and error, the current iteration is pictured below. I'll put additional images and information on the project as time permits.

The bike crank turns a large, wooden wheel made from an 18" table top from Lowes. This in turn drives a treadmill motor (230V D.C.) found on ebay. At 60 rpm or so at the pedals, you get 25+ volts from the motor. This charges two, 12 volt gelled-cell batteries, wired in series to produce the 24 volts needed to charge our Apple iBook laptops. I put two large diodes in the circuit, one between the motor and batteries, and another between the batteries and the laptop, to ensure the current flows in only one direction.

Output was stabilized with a voltage regulator built around this Radio Shack part.

I purchased the original bike from megafitness.com, although I don't think they carry this model any longer. As of August 2006, it was available here for under $200. If you search for "Stamina recumbent bike" you can usually find several sources.

I'm looking at having the motor charge an uninterruptible power supply, and then have the original laptop charger plug into its power inverter. I'll post the results of that experiment when available.

I had a lot of trouble with the drive belt coming off (current belt is a 16610 from Auto Zone for about $5). I found a small, v-pulley from an old well pump that replaced the motor's wheel shown above. The belt now stays put, but I need to put a tensioner on it somehow.

Any suggestions on a table for the laptop would be appreciated. This projection stand is too high for the kids. I'm thinking of an articulated monitor stand.

Our students typically do much more "mousing" than keyboarding, so I'm looking at adding a trackball, closer to the seat, to facilitate that.

Below is one of our fine students, Howard H., riding on the unmodified bike some time ago.

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