This is a very simple and cheap vertical axis design, using easy to come by parts. It is also very easy to assemble, with the minimum of machining necessary. Drilling a few large holes is as difficult as it gets.
And of course it allows you to reuse some of that empty soda bottles you have lying around!
Step 1: The Basic Idea
From Wikipedia: Vertical-axis wind turbines (VAWTs) are a type of wind turbine where the main rotor shaft is set transverse to the wind (but not necessarily vertically) while the main components are located at the base of the turbine.
In this kind of wind turbine the blades turn around a centre vertical shaft. The blades are often cupped, with the cups facing the wind in turn, resulting in the turning of the central shaft.
In our wind turbine the blades are made of three empty Coke/soda bottles cut in half and mounted on a cheap plastic tray. The tray is fixed on a longish bolt (centre shaft) onto which skate board bearings are fixed with nuts to facilitate turning in the wind, and mounting to a base.
In the video you can see it working.
The photo shows the basic construction of the turbine shaft. From the right hand (top) side, you've got the following: Plastic spacers, because the thread of the bolt I used stopped about 5mm below the head. Then the plastic tray (represented here by a sliver of wood) fixed with nuts between two biggish washers. Next two skateboard bearings fixed between two nuts. The nut between the bearings act as a spacer to enlarge the mounting depth of the bearings for more stability.
Step 2: The Parts
The photo shows all the parts for the basic turbine:
1. Plastic tray with a diameter of 30 to 35 cm
2. 8mm bolt 125mm long
3. Four 8mm nuts (or more if you want to use extras as locking nuts)
4. Two biggish washers with 8mm holes
5. 2 skateboard bearings with 8mm inner diameter. The ones I used had an outer diameter of 22mm and a thickness of about 7mm.
Of course you'll have to mount the turbine on some sort of base, and I'll suggest one later in the instructable.
Step 3: Construction: the Bottles
Any 2 liter soda bottles should do. Cut three in half as shown in the first picture. I used a band saw, which was a messy, noisy, somewhat dangerous, but very quick operation. Scissors, a sharp hobby knife or some kind of hand saw should also work well.
The existing caps of the bottles will be used to screw them to the tray. They need holes in them for rainwater to drain (second picture).
Step 4: Construction: the Tray
The tray I used cost me less than the equivalent of $1.50. Choose one made of bendy plastic, which will not shatter when drilled or bent.
We have to drill three evenly spaced holes near the edge of the tray to fit the threaded part of the bottle necks through. That means they will have to be at angles of 120 degrees from each other. The first picture shows the angles being measured out. In the second picture the place for the hole is marked out with an awl.
The size of the holes can be anything from 26 to 29mm. The optimum is 26, but the larger sizes also work well. I used a hole saw (third picture) which gave me holes of 29mm. The second last picture shows the drilling of one of the holes. (I use the small discs left over [last picture] later on as spacers on the centre shaft.)
The centre of the tray must get an 8mm hole for the centre shaft/bolt.
Step 5: Assembling
Now we just have to screw everything together.
First the 8mm bolt is fitted through the tray from the bottom side (first picture) with one of the washers (the tray is used upside down to prevent rainwater from collecting in it), and fixed from the other side with the other washer and a nut (see second picture)
Then the two bearings are fitted to the shaft/bolt with nuts as shown in the second picture. The distance between the tray and the bearings is determined by the thickness/depth of the tray's rim. When the turbine is in use, the rotating tray must of course clear whichever base the assembly is fitted to.
Next the bottles can be fixed to the tray. You just screw them to the tray as shown in the third and fourth picture. The open "face" of the bottles must be aligned perpendicular to the edge of the tray, all three facing the same way along the perimeter of the tray (fifth picture). The way they face will determine if you turbine turns clockwise or anti-clockwise. The one in the fifth picture will spin clockwise.
If your bottle holes in the tray are bigger than 26mm, you can remove the white sealing rings on the neck of the bottles and refit them upside down (last picture). Their bases are broader than their tops, providing a more secure fit in bigger holes.
Step 6: A Base
The basic turbine is finished now, but what about a base to fit it to?
The kind of base you use will probably be determined by where you want to use the turbine. Maybe you have an existing pole or fence you want to fix it to, or maybe you want to use it on its own somewhere in the open.
I had an existing fence pole I wanted to fix my turbine to, so I'm going to show you the base I used. It should be simple to adapt it to suit your needs.
As can be seen in the first photo, the base consists of a T-piece made out of 18mm wood. The leg of the base is fixed to the fence pole with cable ties through 4 holes drilled in the wood. The bearings of the turbine is clamped in a 22 mm hole in the horizontal top part of the base (second picture).
The last picture shows the construction of the "clamp". I drilled a 22mm hole (the size of the bearing) with the spade bit shown. I then made a 2 mm wide cut from the edge of the wood right through the hole stopping only about 80 mm further. This allows the hole to open up to accommodate the bearings, and then be clamped shut around the bearing with the screw shown in the picture. A bolt and nut would be a more secure clamping device than the screw, and I will change the screw for that sometime in the future.
Now your turbine is ready for use, but I still have one more modification you may want to apply.
Step 7: Improving Sturdiness
Although the soda bottles on their own should be quite resilient to wind, one more modification will enhance their sturdiness for more peace of mind. That is joining the tops together with some sort of light framework.
There are many ways to do this, and I used what I had at my disposal: A piece of broom handle, some bamboo skewers and small cable ties.
I drilled three 4mm holes (diameter of the skewers) 120 degrees apart in the sides of the piece of broom handle, and glued the three bamboo skewers into the holes (second picture). Then I drilled a 3mm hole (width of the cable ties) into the bottom of the soda bottles, and fixed the frame to the bottles with cables ties and some glue as shown in pictures three and four. Of course the skewers had to be cut shorter to a suitable length.
And there you are, turbine ready for use! Of course, if you want to use the power the turbines produces, it should be easy to attach a device to the threaded end of the shaft/axis.
(Note: I've only use the turbine in moderate winds, and do not know yet how gusty a wind it can endure.)