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Let me say up front that the copper pipes and pipe fittings were handy and are on loan from my boss - he's got lots of scrap gathered up from over the years - it's not soldered together and will get replaced with pvc. I didn't have enough 3/4" pvc fittings laying around is all. I think when I switch to pvc for the frame I'll bring the pole down the center line of the vawt. I'll probably use a galvanized conduit pipe for the pole and will want to add guy ropes to it with stakes on the ends....think camp charger.
The OD on the rollerblade bearings is the same as the ID of 3/4" fittings which is handy. For some reason I'm using two sets of bearings on each end as you can probably see in the second picture but I doubt I need to. I'll remove a set from each end later and see how that works out.
You should be able to see the flat "L" corner braces turned into a "U" bracket. I don't like that there's only one bolt on each end holding the pvc on but these 1inch "L"s were the best I could find. Having just one hole makes it easy to align tthough - so if you plan to make one and you can find better Ls (or "U"s, let me know!) with 2 holes then start with one bolt, get it aligned, and then drill the pvc and set the other bolt.
The air gap is 1 and 1/4 inch on this one. On the 4" version it was 1". I don't care so much about efficiency though so maybe more/less gap would be better. You can easily change the gap though by changing how you mount the blades and adding extra nuts.
I'm not sure if top/bottom plates add efficiency to this or not, I've just never tried adding 'em. Some kind of bottom plate will be needed to protect the bottom bearings from rain (which you'd need for the alt anyway) so if you're a symmetrical kind of person then a top plate would be required too.
I think this part is pretty much in the bag at this point. There's not much to it and all these parts together shouldn't cost too much. Garage sale rollerblades, some pipe and pipe fittings, 4 Ls and some bolts. The only thing left is the alt, really. I guess that's the tricky part though so I'm all ears as far as that goes.