The Back Story
A couple of years ago I got to sit in on a demonstration of a really cool inquiry based lab run by Mark Davids. In this lab each student group is given a Genecon Hand Crank Generator. They are then told to "play" and record their observations. They quickly find out that cranking the generator is much harder with a load (moving electrons = work) and the capacitor stores electricity in some way. After playing for a little there is a class discussion to share ideas. These ideas can lead to quick experiments to confirm or refute these ideas. This was one of those "AH HA" moments for me. It was a very influential experience and has changed the way I approach many of my labs.
I haven't been able to do this lab with my class. I only have one Genecon and I don't have a large enough budget to justify buying 10-15 of these at $50 each.
While cleaning this summer I stumbled upon a flashlight with a hand crank that I'd bought my son for our last camping trip and out of the blue I had a Genecon? How much do they cost? ($8 at Amazon) As it turns out I had a couple at school that a student had brought in for a project relating to generators, but in the end we didn't use them (he had gotten them for free).
Note: I just bought some at Home Depot (16 December 2008). They're in packs of three for $10!!! They're a little different but they work fine. I'll post some pictures soon.
I haven't used these in a classroom situation yet, so I don't know if they will be as robust as Genecons. But at $9/ea they are not much more than the $7 Genecon replacement gears. The output seems similar. I haven't done extensive testing yet, but load voltage is about the same for the same load.
Update - March 2012
I've used my DIY generators for a few years now. They work ok, but they are not quite as durable. I just caution students to not be "stupid". If they just do the lab everything is fine, it's when they try to see who can go the fastest or they hook two together and crank against each other that there's a problem.
My friend Jim Gell tried it and says:
Step one - Stuff You Need
Mine had four small screws that came out fairly easily. I then had to pry off the black rubber grips from the sides. They were glued on in such a way as to hold the two halves together.
Step three - Remove the Electronics
Look for small screws holding the circuit board down. There was one small screw on mine. It's kind of funny. I had two flashlights that came from the same source and yet the electronics were different (see the pictures). Save the electronics. Here you have three bright white LEDs, a 3.6v rechargeable coin cell battery (be sure to dispose of this properly), and a charging circuit.
You'll also need to clip some wires. I had two sets to deal with. One from the motor and one set to an external port that you can use to charge other stuff. I left the wires from the motor as long as possible to make later steps easier.
Step four - Add the Alligator Leads
I used two different colors, but avoided red and black specifically. I want there to be a difference, but I want them to be able to figure out which way the electricity flows. So just get two different colors of leads, cut them in half and strip the ends (save the other half for another one). Vital Step: Find the bit that the LEDs poked out of. Feed the cut wires through the holes. This is much easier to do before you solder them (this is the voice of experience talking). You may also want to tie a knot in the wires to make it harder for students to rip them out. Now you can solder the leads to the motor. I always find it easier to solder to wires than directly to a motor. That's why I left the motor wires intact.
I tend to be a belt and suspenders man when it comes to building things intended for student use. So even though I tied a knot in the wires I hot glued them as well. I hot glued the solder joints down and I glued the wires in place where the protrude through the holes.
Step five - Put it Back Together
I used a little hot glue around the LED holder (focusing mirror thing) and to fill in the third, unused hole. I want to make sure stuff won't be able to get in and foul the gears. I also used a little hot glue to glue the grips back into place. You may be wondering why remove the guts? Why not just use the output port? Or, why not buy the iPod charger Harbor Freight sells for $8?
The charging circuit still pulls a load in the flashlight even when the light is off. I want students to feel the difference when they crank with a load vs. no load. The I-Power is cool, but I also want to be able to crank the handle in either direction and I want it to turn when electricity is put back into it, say from a super capacitor.