Well I finally have a tower stub put together. This is the part that the wind turbine (the yaw bearing actually) slides over at the very top of the tower. The wind turbine needs to pivot or yaw in order to point towards the wind. You may be surprised to find out that people don’t often use ball bearings for this moving part. I assumed at first that pillow block bearing or something like that would be best, but not so. They mostly use this kind of tube over tube design with lots of axle greese and sometimes a bronze or plastic bushing between the steel tubes. It turns out this design will keep the metal parts lasting plenty long, and it is actually prefered because the added friction keeps the turbine from nervously jittering back and fourth to face the changing winds. This way the turbine appearently stays pointed in the direction of the prevailing winds and produces more power. I like this keep it simple stupid approach since it is cheap and extremely easy to build…sometimes it is better not to over engineer something simple that just works.
I decided to build my tower stub a bit different from the design in the Homebrew Wind Power book. Instead of simply sliding the yaw bearing over a 2 inch pipe with some grease, I decided to use a slightly smaller diameter tube so I can slide a bronze or plastic bushing down the entire length of the tower stub and place a bronze washer at the top.
Below you can see the 2 inch piece of tube I started with. The outer diameter is exactly 2 inches. Look how crazy thick the walls are on this tube!!! This is expensive tube that I found in the scrap yard for only 40 cents a pound. The yaw bearing would never wear through this even if there were no bushings. It took 15 minutes to make one cut of this tube with my new steel cut-off saw!!!!
Anyway, I welded it to a 1/4 inch thick sqaure plate that can be bolted or welded to the top of the tower.
Below is the steel cap I welded that slides over the top of the tower stub. You put this on after sliding a section of 2 inch bronze or plastic down the length of the tower stub. This keeps there from being any steel on steel contact down the vertical legnth of the yaw being. I am going to order a bronze bushing tonight that should fit just right. I am also ordering a bronze thrust bushing that sits on top of the steel cap and keeps there from being any steel on steel at the top of the yaw bearing.
Above you can see the tower stub with a section of PVC and the steel cap. PVC was my first idea, but since I found a website you can order bronze from I have decided to use it.
When we are ready to set this thing up we will grease the entire tower stub, add the bushing, and finally slide the entire alternator assembly over the top. That is all there is to it. The grease and bushings will allow the wind turbine to spin around and face the wind.
I just ordered the bushing from the website below…