I was first drawn to instuctables by a wind turbine. I keep reading wind and water turbine post but have yet to get around to building one. Many make use of cycle wheels most seem to dispose of the wheel bearings and use a solid bar as a combined axle and use the tubes of the wheel as a sleeve bearing. To my mind this adds unnecessary friction into the system. I asked the last author of a water turbine I saw do this why they didn't just extend the axle and utilise the low friction wheel bearings. The reply I got was.. How? This is how I'd do it. As it isn't load bearing it will require both outer ends are solidly supported.
Step 1: Select
Find a length of steel tube with a a thick wall the bore of which is a good fit on the wheel axle. For some reason the front and rear axle tend not to be the same diameter so if you are using a pair of wheels salvaged from the same bike one of the axles will need building up with tape or a strip of metal cut from a can.
Step 2: Drill
locate the seam in the tube It shows up nicely as the dark stripe on this tube I have,rotate the tube 1/4 turn and then file a small flat on the tube roughly where it needs to be drilled. This wants to be about half the length of the sticking out axle but far enough along it that you will be able to drill the axle. Round stock is a pain to get a drill to start in and trying to drill through a welded seam is just making things unnecessarily hard. Place a bar inside the tube and use a center punch to make your starting dimple on the flat you've filed. Use a smaller drill than your intended end size to drill a pilot hole, once through the first wall check the drill is going across the diameter of the tube before drilling the second wall. open the holes up to their final size with a larger drill bit. As this axle is about 9mm - 3/8" I've made the final size 3mm - 1/8". place the tube on the axle and use it as guide to drill it.
Step 3: Pin
I used a 3mm machine screw and a nut to pin the axle of the cycle wheel to the extension, the other wheel would be attached in the same manner. Tie rods and turbine blades can now be attached between the rims.
Step 4: Utilises the Sprockets
I think it is worth mentioning that the free wheel only works in one direction. If the wheel is turning clockwise as shown the free wheel will function and the sprockets will just click around on the ratchet. If how ever the wheel is turning anti-clockwise the sprocket will be driven by the wheel. If the turbine blades are arranged so the wheel spins anti-clockwise the sprockets can be used to drive the generator. Whilst the gear ratio might not be as great as a drive belt from the rim a chain is less likely to slip.