Step 1: Get some 25mm ID / 50mm OD bearings
Prise the side seals off and scoop out all the grease, then rinse the bearings out with some diesel or turpentine to make them spin easier, then pop the seals back in. They should spin easily now.
Head down to the hardware store and find a cheap broomstick handle that just fits inside the bearings. Dont worry if its a tight fit.
While you're at the store buy some 50mm (inner diameter) PVC tube and 2 large buckets (I found about 20 litres ideal).Also uy some long screws - I used plaster screws at least 50mm long.
Step 2: Make the shaft
Tap 2 bearings to be close to the center of the broom handle, then slide the 2 lengths of the PVC tube and tap it down so its a nice tight fit, then tap another bearing into each open end of the tube.
I also fitted an end cap to one of the tube ends, as well as a bell shaped fitting to keep the rain out (see picture). Screw the top piece to the broom handle in the center so its fixed to the broom handle. The broom handle has now become the center drive shaft.
Check out the video - you now have a free spinning drive shaft - I have a small piece of dowel I drilled into the bottom of the broom shaft to show rotation while clamped in the vise.
Step 3: Add the VAWT blades
I used an electric saw and just held it there while gravity did all the work. You could use a handsaw easily.
Then use a holesaw to make a hole in the top of each half, so it will fit over the top of the broom handle sticking out of the top of the shaft.
Please be careful and take the time out to think at each stage - the author accepts no responsibility for sloppy planning!
Step 4: Add a blade
Add some screws down the side - by using thread on the screw you can the leave a gap between the blade and shaft as it increases efficiency.
Step 6: Add the other two blades
Remember to cut 50mm holes in the top of each bucket half so they fit onto the center shaft.
You can drill small holes where the top 2 blades meet the bottom two, and tie the blade sets together with wire or cable ties. This really stiffens the whole strucure up nicely.
Step 7: Trial run
You can see from the little coloured toy windvane that even though there's no wind, it starts in the lightest of breezes. It has a truckload of torque too when the wind is aout 20 kilometers per hour.
In the second video I have added two large blades from large domestic garbage bins. I tried grasping the broom handle and stopping the centre shaft coming out the bottom - too much torque! Tonight I'll add the other two blades. With a much larger blade radius I should be able to pull a lot more watts off of it!
Step 8: Time to make some power
With the following assumptions:
m(air) = 1.2 kilos per cubic meter
area(frontal) = 0.7 square meters
windspeed = 5 meters per second (about 15 kph)
Then Watts = 0.5 x 1.2 x 0.7 x (53)
= 52.5 watts
However Savonius Vawts seldom do better than 30%, so I better find about a 20 to 50 watt DC motor somewhere to try it out.
Check back soon...