Saturday, October 13, 2012

human powered machine workshop


In the summer of '10 Aprovecho hosted a workshop on pedal powered machines which i had the pleasure of planning and teaching with my friend Neil Kearns (check out the previous post to see one of his machines).

A handful of folks came from around the country and Canada to learn about pedal powered machines and to collectively build an electricity generator.

Neil and I built a generator in advance of the workshop to ensure that we had a solid working model to base the design off of. This is what we came up with:



The workshop started with an introduction into the basic concepts of using human power- gear ratios, drive types, efficiency, etc. (I won't go into detail about those things here, but if it's something that you are interested in i'd highly recommend picking up a copy of The Human Powered Home).

We started in pretty quickly to building the generator. As an instructor, once more, the challenge was present of how to keep everyone as engaged as possible. There were some lag times for sure, but overall things stayed pretty balanced. And if i remember correctly, i only had to jump in once or twice to help with the welding, otherwise it was all the students.



The generator that we built used a deep cycle lead acid battery (like the kind made for RV's or small boats). A small motor pulled out of a "dead" treadmill on craigslist. A multimeter, a diode (also pulled from the treadmill), an inverter and a whole mess of wires.

I'll explain a little more about the components we used. Deep cycle batteries are designed to hold a significant charge and release it over a sustained period without needing a recharge. These are much better suited for a DIY generator than a car battery. Car batteries are designed to be charged and dispelling electricity constantly. One thing holds true for both batteries though- never drain all of the electricity. Both types need to maintain a certain level of charge in order to function properly.

To make sure that our battery wasn't undercharged, or overcharged, we hooked up a multimeter to tell us both the charge level of the battery and how much electricity was being produced at any given moment via pedaling.

You may wonder what the motor is about, well, a cool fact about electrical motors is that you can use electricity to make them spin or you can spin them to make electricity. So that's just what we did, set the fly wheel of the motor on top of the wheel of the bike machine, using the friction of contact to drive the motor wheel. The quirky part about using a motor is that if you don't wire it properly you'll start generating electricity with it and once its sent enough electricity to the battery the electricity will come back and start spinning the motor!

As funny as it was to play this little game with the motor, its totally useless for generating anything. That's where the diode comes in. Diodes are semiconductors, often used on circuit boards, that control the flow of electricity. Soldering in the diode into our circuit kept all of the electricity from rushing back out of the battery and into the motor.

Inverters are devices used to change electricity from direct current (DC) to alternating current (AC). When using a re-purposed motor to generate electricity, direct current is what you get. And while there are some things, mostly RV or marine-based, that use DC, just about everything else uses AC. (There's a long and fascinating history behind the two currents, which i won't go into, but its definitely worth a look on wikipedia).

And the wires, well, you know what those do.

Here's a video of the generator powering an angle grinder. Kindly ignore the cigarette.




If you are interested in building your own pedal-powered electricity generator there are plenty of designs out there on the web. Here's a couple I'd recommend checking out:

http://www.pedalpowergenerator.com/
http://www.instructables.com/id/No-welding-pedal-generator-stand/

Also, before building a pedal power electricity generator you may want to check this out important article from Low-Tech magazine:

http://www.lowtechmagazine.com/2011/05/bike-powered-electricity-generators.html

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