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.
Step 2: Wheel to motor connection
One of the discarded CD-ROMs is put flat on the working surface. The glue will stick best on the printed side. Taking this in account we started with the printed side facing downwards.
The working surface as “seen” through the hole of the CD-ROM should be completely covered. With the working surface protected like that, put a good blob of hot melt glue. The stepper motor is put with its pinion in this blob and kept in place by hand, while the glue sets (takes a minute or so). Before it has set look from above to check if it is positioned in the middle of the CD-ROM. Check from several sides to check it is level.
When you are two to do this, it is not hard to achieve a reasonably good alignment this way. The pinion gear helps and we found no spacers or templates were needed.
When the glue has set the scrap paper is peeled off.
With one stepper motor with a metal pinion gear, the wheel came off when using it. The pinion gear was glued back in the hot melt glue cavity, with superglue.
Step 3: Sandwiching the vanes
The vanes are glued to the CD-ROM already on the stepper motor. We did not mark their position beforehand. Following the pattern show in the pictures, each time putting a van “in the middle” works accurate enough.
Some practical testing showed a second CD-ROM on top is needed to make the wheel-vane construction robust enough. When the glue has set, check the “height” of all vanes and trim those that are longer than the others. All vanes get some glue on top (working quickly) and the second CD-ROM is put on top.
Step 4: On a stick and into the water
Connect the LED to two leads of the stepper motor by either inserting its legs in the plug or by soldering. The polarity of the LED does not matter as the current will be alternating. You will need to check which two leads work by spinning the wheel by hand. Several combinations will work, but (depending on the type of stepper motor) not all.
We were able to test our build in the feed to a real water wheel, but you can use any water running at a reasonably high speed. Be careful at the bank: don’t risk falling in the water. :-)