Heres what you need:
10 X Paper Coffee cups
An old CD
Small scrap of plywood anything above 6mm thickness will do.
A stepper motor from an old printer/fax/scanner/till etc (the older the machine the better usually)
8 X 1N4001 General purpose diodes.
General purpose glue, must adhere to metal.
Miscellaneous small wires
Battery holder to suit batteries
Electrical insulation tape
Note - Not all stepper motors will work well here you must experiment!
Multimeter or ammeter (optional)
Anemometer handy too but not at all necessary.
The video below shows the mini windmill producing some power, the full scale of the meter is 50ma so it's producing around 10 - 30ma typically at wind speed of around 6 - 13mph. It doesn't start charging until around 8.5mph. You can lower the cut-in speed (wind speed that it starts charging at) by just using one ni-cad (1.2v instead of 2.4v). The cut in speed also depends on the amount of cogging your stepper motor has.
There isn't much wind in my garden being surrounded by garden fences, houses and the like, you will get much better performance if you raise the turbine up above everything, but it isn't really worth building such a tall tower for such a small turbine.
Step 1: Mark the Cups Mounting Point
Step 2: Cut the "sails" Shape From the Cups
You need to remove the front section of the cup as shown in the photos but leave the rim around the top of the cup.
Step 3: Make the Sail Extensions
Step 4: Cut the Mounting Slots for the Extensions.
Step 5: Cut the Adapter for the Stepper Motor
You'll need to drill out the centre of the circle to match whatever cog or shaft your stepper motor has.
The adapter should be a tight fit but not so tight you need a hammer to fit it!
It doesn't have to be a circle though you could use a square piece of timber.
Step 6: Drill and Mount the CD.
Step 7: Solder the Circuit Together
Follow the diagram and solder all of the diodes together as well as the stepper motor and battery pack. I used a three AAA cell holder purely because I had it to hand you only need a two cell holder.
Identifying the motor output wires:
To identify the wires from the stepper motor you can use an ohmmeter to measure the resistance between the wire, the two wires that connect to a coil will have a resistance somewhere between 5 - 100 ohms (roughly). If you don't have an ohmmeter you can simply use an led, connect it to different wires until you find the ones that are producing power. When you have identified the coil pairs, twist them together so you don't lose them.
Ammeter Connection :
I left a break in the wires so I can measure the current flowing to the batteries easily you can omit this if you don't want to measure the output.
If you have connected a meter to the circuit you can spin the motor by hand and see how much current it pushes. I measured around 75ma spinning it by hand.
Make sure that you get all of the lines in the right places on the diodes, they indicate the polarity of the diode and must point the right way. As an alternative to soldering the diodes together you could buy ready fabricated bridge rectifiers (they are very cheap) and connect it all together with screw blocks.
There's no reason why you can't connect some LED's in place of the batteries to make a decorative LED wind spinner., if thats what you'd prefer.
Note: I changed the rectifiers to parallel on 26/04/2010 thanks ghurd and trialex
Rectifying other types of stepper motor:
There are 5 wire and 6wire stepper motors too, The Back Shed has some circuits for rectifying these see here : http://www.thebackshed.com/windmill/assemblyMini3.asp
Step 8: Attatch the Rectifiers to the Motor
First of all put a layer of tape on the back of the stepper motor then thread a piece of tape through the centre of the rectifiers to tape them down. Then tape over it all (gently!)
Step 9: Glue Everything Together
Step 10: Glue the Motor in Place
Step 11: Make Some Tent Pegs
Step 12: Test It
If you're using the tent pegs to hold your turbine down, can simply push them into the ground so that they hook into the holes you made in the side of the cups.
If you're mounting the turbine on a pole you'll need to fix the cup at both sides with two screws either side to prevent the cup from tipping, you'll also need to glue the battery holder to the inside of the base cup (unless you don't mind it hanging loose)
If you have an anemometer you can plot the windmills output versus the wind speed to get an idea of how it might perform in different locations
How much power you get depends on the stepper motor you chose and the wind speed. There isn't much wind in my garden being surrounded by garden fences, houses and the like, you will get much better performance if you raise the turbine up above everything, but it isn't really worth building such a tall tower for such a small turbine.