Horizontal Axis turbines are powerful, but require tall, unsightly, and expensive mounts to reach strong enough wind to be worthwhile. Vertical axis turbines generate less power, but are far more visually appealing and can run at lower levels. The logical solution is to combine the two, in order to make a high-power visually appealing device.
So, despite moving thirty miles specifically to ensure that I could make it to my hackerspace more often... I haven't been there in over a week. Even more distressing, somehow the original design that I tried to 3D print couldn't be converted into working g-code -- openscad seems to have something against the rotate_extrude function, so I think that my idea of 3D-printing the bearing cup is probably going to have to be abandoned. To American Science and Surplus I go !
I have had a slight epiphany during my absence from work, and have come up with a far more workable solution than 3D printing to produce the turbine -- injection molding. Specifically, I'm planning on using a CNC autorouter to make the pieces below (the inner piece will be broken up into six flat plates, and only two of the six outer pieces are shown for demonstration purposes), then I will clamp them together into a cylinder and inject polyurethane foam. This will be followed by a layer of chopped fiberglass and resin, to create a lightweight but durable piece. As an added bonus, once I get the proof-of-concept prototype out of the way, I'll have a ready-made mold for finishing a production run. I might be a little overoptimistic right now, but I'm hoping to have a few of these built by the end of the summer.
The CAD files for the test print are done! I listed the "full concept" print as wing.scad in my github, and the actual print file (which is less likely to fail due to lack of support) as wingPrint.scad*. I'm currently waiting for Slic3r to finish slicing so I can start the print and head home.
In the meantime, I've been extracting a vital component of the finished product -- bike wheel bearings. Since I don't want to fork over upwards of $20 or wait two weeks for American Science and Surplus to ship, I'm using the bearings and cones recovered from a bike wheel and adding the cups as an integrated part of the print.
The grease from a bike wheel (especially a recycled wheel like the one that I'm using) is a little too thick, so I used some dish soap and hot water to soak it off, and I'll add a different lubricant in the morning.
*You'll also need the *.dxf files listed on my github in order to compile and export these files.
I've already attempted and discarded a couple of builds. The first and second were the Savoniusturbines I came across on Instructables.com. I've been hampered by a few issues: first, I don't have easy access to a band saw, scrolling saw, or rotating saw, and so splitting the PVC into half-cylinders of consistent height is nearly impossible to accomplish on a reasonable timetable. Second, Savonius turbines aren't particularly powerful, especially when you consider the major increase in the tower's swept surface area that they cause. Third is the difficulty in finding cheap/effective bearings to use to get the turbine spinning.
The third build attempt was a Darrieus turbine with the spinning axis in the center and pylon-shaped airfoils jutting upwards and downwards from it. This would have worked if not for the fact that I used a conic section as my airfoil, yielding a neutral angle of attack and a net outward lift instead of rotational force.
My latest design is a helical Darrieus turbine with a secondary set of blades which serve as the self-start mechanism by transforming updrafts into the initial rotational momentum. Pictures and build logs to be posted later in the week.