We made several attempts, a number of which worked, but those based on a stepper motors from a discarded printer proved to be the fastest an easiest to make. Furthermore, apart from some glue it was completely built out of discarded parts, thus combining the demonstration of renewable energy with reuse.
We had a great time building and playing. Check out the video to see the result in action:
Step 1: Reusing parts and materials
a small stepper motor as found in a printer
2 discarded CD-ROMs
a foam tray
some long stick (I used a piece of 20mm diameter PVC tube from demolition)
one or two tie-wraps
a small piece of scrap paper
Non-reused: The only non-reused part is the hot melt glue (I recommend the low temp type, especially when working with kids).
Tools: scissors, screwdriver to disassemble the printer (not shown), cutting pliers or desoldering tools for (optional, not shown).
Stepper motors make very easy generators, as they produce relatively high voltages (I’m talking 5V range) at low rpm. Small DC motors (toy motors) need high rpm and still produce only a low voltage (1V range). Stepper motors do not need gears and/or electronics to power a LED (compare it to my junior wind turbine). I was worried about blowing up the LED at first, but that did not happen. The current generated being pulsating very probably contributes to that.
I doe not bother to waterproof anything (motor or electronics). Repeated use for several minutes, on several occasions, showed no need for that.
If found two stepper motors in an old Lexmark inkjet printer for which first the ink heads were no longer available and which later did not survive more than a couple of refills of the last ink head. I guess most inkjet printers will have two stepper motors, one for moving the paper and one for moving the head. The way to disassemble the printer will differ for each model. As in this case the printer should be a discarded one and there is no need to put it back together, you can’t do much wrong by simply unscrewing al screws you can find until you can free the stepper motors. Just keep the pinion gear and the connector they come with on the motors. To give you an idea on what to disassemble, you can go looking for an exploded view of your printer, like this one.
With a bit of luck the LED can also be found in the discarded printer. With even more luck you can find some discarded electronics with a LED standing tall on a printed circuit board, with most of its legs still intact, instead of mounted flush on the board. This makes it easier to remove from the print (leave the legs as long as possible) and easier to connect to the stepper motor by simply inserting it in the plug. As alternative you either us a new LED or desolder one and solder it to the stepper motor leads (I guess it is hard to tell if the ecological impact smaller for using a new led or for (de)soldering).
To keep within the spirit, you can also reuse tie-wraps: when you cut them loose carefully near the “ratchet”, you end up with a shorter, but still usable tie wrap.
Now to start building, see the next step.