Wednesday, October 28, 2009

Wind Turbine Blades by CNC Router

by Brian Rodgers

First off our turbine is an Otherpower design built from the pre-published Home Brew Wind Power book we received after a week long class in Colorado. Sweet

I highly recommend Dan Bartman's and Dan Fink's classes to everyone considering building a wind turbine.

So,this is actually our second 10 footer, but we soon found out building a wind turbine at the Other Power workshop is a whole heck of a lot simpler than gearing up and building one in our living room.
Before we did much more than build a stator on the kitchen table I decided we needed a shop.

It only took a year to get the shop usable. On the bright side it wasn't expensive and we had loads of help from friends and family

Anyway our system is a 10 foot wind turbine mounted on a 46 foot, guyed, tilt up, 3" square tube tower on top of the hill we picked specifically for best wind and no few trees nearby, which performed poorly. With the decent mountain winds of 20 to 45 mph (guestimated) the turbine was putting out a meager 8 – 10 amps @ 24 volts. Then I caught sight of the ammeter in a few super winds, maybe 50-60 mph, it hit 25 amps, even while furling, finally, proof that our alternator could actually make the juice we hoped for.

It was back to the drawing board and in our case being computer geeks, back to Solidworks 3D modeling and Mastercam  G-code (CNC machine code) generator. Kevin's dad has been a pilot since forever, and he convinced us that the airfoil shape in the Other Power book was efficient only from a hand carving view point. A machine designed and cut blade can have negative curves for instance, similar to what we see on the bottom of PVC blades.

Kevin set about building faster, sleeker blades. I suggested we add six inches to the five foot blade just to pull a bit more energy from the available wind. So, what you see in the above design is a five foot six inch blade 1.5 inches thick  and 7.5 inches wide at the root. We also increased the blade area by cutting back the root by nearly five inches, leaving just enough room to mount the 10 inch plywood disks which hold the blades in position.    

Just in case you wonder if an eleven foot blades set will fit on our tower without hitting the guy cables. Yes we actually have a six foot two inch (id) schedule 40 pipe stub on top of the tower. That stub top was actually kind of a mistake, but it seems to be holding up even though I have seen it flex a little in those super winds. Next tower is going to be made from much larger material and the stub will go nearly to the top.
Anywho, this was a test setup, so it doesn't matter if most of the wind turbine and tower were made from what we had on hand, indeed that was a main part of the experiment. In fact, while we struggled to get the turbine in the sky before the notorious Spring NM winds I wondered which part of this system would fail first. Knock on wood all of our ranch engineering has held up to everything nature has thrown at it.
We will need to calculate a new tail to match the new blade sweep area, but building wood pieces just got o whole lot easier now that we are hooked up with a local cabinet shop where the CNC router now is setup. Boy howdy, we have tools, all kinds of tools: Last night before leaving,  we quick cut up three 4"X4" Douglas Fir cants using Louie's crazy cool 18" band saw. Once we had 12-2"X2"s we ran them through a planer, spent considerable time sorting the wood for grain direction and putting knots in places which are outside of the area the router was cutting, we began gluing and clamping.

The cabinet shop owner was a bit of perfectionist to say the least and he kept us doing a good job the whole day, OMG, no wonder we're exhausted. But that was cool, nothing like having a journeyman cabinet maker excited about homebrew energy making. So yeah, if you see any imperfections in the wood it wasn't because our resident craftsmen didn't make enough pencil lines on the wood as we were sanding, "this spot needs work, run you hand over it, you should be able to feel it."

That's it then, probably not a second to soon for some of you.
Obviously I like chronicling

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