Small wind turbines have lower energy output than commercial wind turbines, such as those found in wind farms. Commercial generators in the 5-50W range are available for boat or caravan use.
While this particular model is made from a 24 oz. water bottle larger models with blades cut from a 2 or 3 liter soda bottle and using a cardboard, plywood or sheet metal end pieces should be efficient enough to drive a generator based on a fan motor such as those found in old CPU cooling units.
A 12V .09A CPU cooling fan connected to this assembly could produce as much as 1W under the right wind conditions. This is more than sufficient to recharge NiCad batteries and other trivial energy needs, or fed into an existing inverter as a supplemental power source.
With some scaling and good gearing it should be possible to reach as much as 25W using this basic design.
I would like to thank rhackenb for his most excellent and inspirational 'ible Cardboard Savonius Wind Turbine
With that in mind lets get started....
Step 1: Bill of Materials
A protractor - That thing for drawing circles
A compass - The half circle that comes in the package with the thing for drawing circles
A soda bottle. Almost any size will do and the directions will scale up or down as available. I used a 24 oz. water bottle.
Something to use for an axle. I didn't get fancy I used a wooden skewer from a pack of 100 we had in the drawer. Future designs which are used to power generators will probably have a two part axle ( top and bottom ) and not carry the extra weight in the center.
A couple of paper plates or other cardboard for use as the end pieces
Step 2: Cut out the Fan blades
Carefully peel the label off of the bottle. Don't worry about the glue, its tedious and I haven't found a good way to remove it...yet.
Using a Sharpie mark the midpoint in each node ( see picture ). We will use this to cut out our fan blades.
After all the sections have been marked off use the Sharpie and a ruler to mark a straight line down the flat portion of the bottle. This will be our cutting guide.
Cut off the top and bottom of the bottle. Be careful, I used a hobby razor knife but scissors will do nicely. A word of advice, cut and then trim. Do not attempt a fine cut on the first pass. Cut off the top and bottom well above and below the center then trim off excess.
Okay now cut down the lines we drew earlier. This will create 5 even blades. Trim and square off the ends of the blades to a common length. I arbitrarily chose 4 inches although I probably had close to another 1/2 inch available. More if I had cut carefully...
Okay our blades are ready, now lets cut out the wheels.....
Step 3: Create the wheels
Using the bottom of the soda bottle and the marks we made on it mark off 5 lines from the center to the end that correspond to the center of the base.
Now measure in the width of your fan blades, in my case if 1 3/4 inches. Draw a line at a 40 degree angle. This will be used to set the blades in place. Note the protractor hole in the center.
Its not absolutely necessary to mark both the top and the bottom. I only marked one and used visual alignment (more or less) successfully.
Once you've cut out the wheels your ready to assemble your wind mill...
Step 4: Assembly and Test
Notice I cleverly used a box to hold the windmill during assembly. This worked out extremely well and I highly recommend a similar arrangement.
In this version the fan blades are attached to the wheels with tape. I found it useful to attach a tape tab first ( see picture ) and then attach it to the wheel. Align the tips of the fan blade along the 40 degree line facing outward ( see picture ).
Once a blade has been attached properly at one line it up so that its straight and attach it to the opposite wheel. I tried both ways and found that doing both ends at once seemed to be easiest.
Attach the blades on opposite sides and the weight will balance out.
When you're done you'll have a lovely 5 blade vertical axis windmill. This design can be stabilized and scaled up for any number of hobby or mechanical projects.