For Sustainable Energy, our first project assignment was to “prototype a portable, personal electronic device wherein the electricity is converted from kinetic energy supplied by the user”. Christian Croft and I chose to focus on energy generated by the feet. For this, we took two approaches – one harnessing the energy of footfall and the other of a spinning wheel in Heelys, the ever-popular rolling shoes.
For harnessing the energy of footfall, we developed a plunger-like system where every time you take a step, a magnet is pushed up through a coil and then falls back down again. Here is a video of our initial test:
We hacked a shake flashlight and made use of the magnet and coil. Our prototype, which was set up to charge a AA battery, looked like this:
Unfortunately, the mechanics of this system do not make for easy walking and slowing down the passage of the magnet (for the footfall, as opposed to the quick shake of the flashlight), produces only a very small amount of voltage, so this model does not seem particularly practical.
Our second model, the Heelys hack, was more successful. We sliced off a piece of the wheel and attached a gear:
This gear interfaces with a gear on a stepper motor so that when the wheel turns, it turns the motor causing electricity to be generated. We tried two different motors, the larger, more powerful one being the more successful of the two.
Cutting the hole in the sole of the shoe for the stepper motor is a bit laborious, as you can see here:
However, it is well worth the effort, as the shoes are able to generate up to 8 volts and 400 milliamps.
For our class demonstration, we hooked up some LEDs and buzzer. However, we have plans for pursuing this energy sorce in more interesting applications.
