CNC made wind turbine.

[MrBean]

A while back, a few people here exspressed an interest in small home made wind turbines..... I have completed one made almost entirely on my homemade CNC router.
It's turned out pretty crap to be perfectly honest, but it was a good learning experience for designing and cutting parts on the CNC. I learnt a few things about wind turbines too. ;-) If you haven't seen it already and want to take a look, you can see it here.
http://www.build-a-windturbine.com


Not to be defeated, I've started on another one. Not so much CNC going on this time tho', but some may still find it interesting.
http://www.homemade-wind-turbines.co.uk

You are more than welcome to take the piss, if you feel the need. I sure had a good laugh when I saw the power output. If nothing else, it's good fun and keeps me out of trouble.

Regards Terry.....

[skippy]

Hi Terry, I checked out both sites and have to congratulate you on getting it done. As Benny would say "there's the doers and the lookers" and you're in the first group.
I'm interested in this field and live on the edge of a small cliff next to the mediteranean sea but the only thing is that the wind never seems to blow much here so I guess that rules out a wind turbine. In the second site you say "Later on I can CNC cut some larger blades with a proper airfoil profile." (A) How did you come up with the shape of the first ones? Just a visual copy of what you had seen on other internet pictures? (B) where will you get the "proper airfoil profile" from?
Good luck with it all!
Skippy

[MrBean]

For the blades, I just drew what looked like a good airfoil and shape. It was a guess based on looking at different wind turbines I've seen on the web. I have since found that there are blade calclators for wind turbines, to give some guidance on the blade shape and twist. There are also downloadable catalogues of airfoil profiles on-line. I shall be using an airfoil from the catalogue.
I haven't decided what I'm going to do for the blades on the new wind turbine. I may just lash up something quick and easy when I get that far, and then CNC some proper blades when I have more time.

Regards Terry.....

[ToyMaker]

There are some hints about airfoil shapes and producing them here http://www.otherpower.com/

robotic regards,

Tom
= = = = =
"If nature had named it, it would be called a 'flutterby' and not a 'butterfly.'"
- - Edward Merrill

[Evodyne]

Terry,

Glad to see your hard at work. MkII already. Whew! Build looks good. What are your design parameters or goals? Have you settled on a size/diameter? Are you going to reuse the original alternator or build another?

I thought your blades looked quite nice on the first model. My question with wood blades is balance: if I built some big blades, what is the likelyhood the mill would shake itself to pieces due to not quite equal wood densities. Not sure if a static balance on a three blade equates to dynamic balance or not. I'm wondering if wood scales well to 10'-12' long blades.

Like you I've gotten quite a bit of info off the web. Picked up Hugh Piggot's plans too. All the "easy" blade designs use a first approximation (no "slippage" in the wind) to arrive at the twist and taper. I've started working on software for a slightly more precise calculation using Glauert Blade Element Theory (look here). The only bugaboo is that you need the polars for the airfoil you've chosen at the right Reynolds number. One good source is the UIUC Airfoil Data Site. When I've something to play with I'll send you a copy.

Lance/Evodyne

[skippy]

Lance, now after looking at the link Tom provided (http://www.otherpower.com/) I see that there are wind turbines capable of producing usable power from winds of just 5mph so maybe I can start to look more closely at this.

On another note, has anyone seen an article on a wind turbine with adjustable pitch. Seeing as most of us at "the zone" like machining, inventing, tinkering and or helicopters, I thought that an adjustable pitch version would make an interesting project.

Keep us posted (here) on your software progress.

EDIT Just read your other post regarding foam carving a blade. Good idea! What were you thinking? Cover each blade with a layer or two of fibreglass or leave it as raw foam? Actually now that I think about it, Gerry posted a note not long back about some type of paint that you simply brush on to the foam to weatherproof (including UV) it. It is used for outdoor signage, displays, etc.

[MrBean]

Lance. My design goal was to build a better turbine than the MK1. I'm making a new alternator using 10" steel discs, larger magnets and 3 phase. This will be much heavier than the wooden MK1 alt, so I needed a stronger construction, hence the front strut from a car.
Blade size... Hmmmm. I'm going to see how much power the alternator produces at various RPM's, and decide on a blade size from there. I've given myself a max size of 2 metre diameter.
I don't think static balance would mean you would achieve dynamic balance. If the wood had a higher density nearer the tip on one blade, that blade would get "heavier" than the others as the mill started to rotate. I'm not sure how much of a problem this would be. On my MK1, one blade has much denser wood than the other 2. I've seen the mill spin at over 1500 RPM and it does not vibrate or wobble.
Your software sounds interesting. Can't wait 'till you get something we can play with. I've been looking through the catalogue here.

http://www.risoe.dk/vea/profcat/WWW/HTML/index.htm

Skippy.... Adjustable pitch. Now that would be cool. I thought about it for a bit, but it seemed too much work at the minute. I'd like to get a mill up that generates some usable power first. May be I'll try something out once I get more time. Were you thinking electronics. May be monitor the RPM and read the blade angle from an attached potentionometer. A comparator could read the RPM (derrived voltage) , compare it to the Angle (pot voltage), then adjust the blade angle using a motor to match the two values. I may be way off. I'm not great on electronics.

Better get back to it....
Regards Terry.

[skippy]

Terry, yes I was thinking of electronics but now that you pose the question, I can't see why it couldn't be mechanical either. I also am hopeless at electronics but I'm sure there aren't too many circuits that are simpler than controlling the movement of an item (in this case the pitch) according to the rpm or voltage. It's much the same mechanism as a helicopter rotary wing uses (I think that's what they call the propeller thing that wizzes round and round, excuse my lack of correct terms) which is external or that which is used by the prop of a light plane (internal). If electronically controlled, the stepper motor controls the positioning of the swash plate (which controls blade pitch) OR if mechanically controlled, centrifigal force acts upon two or three spring-loaded, rotating counterweights (same as the automatic clutch in a motorscooter) which act upon the swash plate to contol pitch.
"I'd like to get a mill up that generates some usable power first" I totally agree as modifications/improvements can be done at any time later.

Lance, have a look at this: http://www.demandhotwire.com/twister.html

[10bulls]

Fantastic stuff Terry...
I hope by the time I get round to building one you would have sorted out all the tricky bits
Dare I raise the ugly question of planning permission? When I last enquired, I think anything up to 1m diameter was planning exempt, but over that you may need permission. I suppose it would depend on the local council, height of mast, your neighbours and if your local planning inspector has been getting any lately...
Keep up the great work!

[Evodyne]

Hi gang.

Skippy-thanks for the foam cutter link. You're right-you can get good power from wind turbines, if you live where there is reasonable wind. I'm fortunate to be fairly close to Lake Michigan and have a good expanse of open land. Our power supplier just got approved for net metering too. Net metering simply means I can now pump power back into the grid and my meter either slows or runs backwards. At the end of the month I pay the "net" difference between what I used and provide. All in all I think it's a more elegant solution and easier to implement system than battery banks.

Terry, I think you are right on track to spec. your alternator first then match the blades to it. Obviously, if you look at it as a collection of "sub-systems" then it will work best if each part complements the rest. Good luck!

Blade pitching extends this "complementing" process by allowing you to match the turbine to the wind conditions/rotational speed. Here is something I want to pursue, based on some aircraft tests...free rotating blades that set their own pitch without mechanical control. Here is one link; more are here , and here. Essentially, let the physics of the system set the blade pitch. See my crude attached picture of what's in my mind.

If for the moment you'll say "O.K, that could work", I'll take it one step further. We have, by virtue of the pivoting blades, matched the "propellor" part to the wind conditions. Now we need to match the torque required to turn the generator to the power available with the given wind conditions. We would like to unload the alternator in light wind to allow the blades to spin at least some. Yeah, we aren't going to get much power out, but we get none if we don't turn the blades! Conversely, in high winds, we have plenty of power in the wind and would like to have an "uber-alternator on steroids".

This alternator tuning would be similar to wind powered pumps that use stepping motors to vary their crankshaft throw to keep the pump load matched to the wind available.

So what would this take? Could it be done electronically? Yep. An open circuited alternator provides no resistance to spinning; a shorted one acts like a brake. One that is rapidly switched between a feeding a load and being open circuited (via big PWM-driven MOSFETS, like a servo drive) will act as a variable load to the blades. The key is matching the PWM duty cycle to the conditions.

Might there be another way? I think so. My thought is that the alternators like Terry has built can:

1. Be stacked to provide more output.
2. Vary their output (and hence load) by controlling the airgap between the stator and rotor.

Imagine a few CDs on a pencil with a generous spacing. As I spin the pencil faster and faster. I begin to reduce the spacing between the CDs, which creates increasingly more electrical output and places an increasing load on me trying to twist the pencil. If I slow, the CD spacing grows and I have an easier time. At some point torque and counter-torque match and I run at a fixed rpm till something changes the balance.

Essentially I'm talking about either a centrifigal or some type of actuator driven variable output alternator, where we increase load dynamically to match the power available.

How practical this is I don't know. I'm hoping we can examine this from all sides. Let me know what you think.

Lance

[skippy]

Lance, now you're cooking! Your idea sounds brilliant. I had an idea this afternoon but it certainly wasn't as good as yours. I was thinking of what I think are referred to as "flex fans" for race car engines. Basically the fan (that cools the radiator on a car) has a steel core but the blades which are rivetted on, are made out of a light springy sheet metal. At low engine revolutions the fan draws maximum air with each revolution and at high engine revolutions the blades flatten out which equals less horsepower draw on engine which is the purpose of these fans. (high fan speed with little pitch plus vehicle movement in airstream is more than enough to cool engine) The same principle can be used in the context of a wind turbine but with minimum pitch at low rpm and at high rpm the blades get blown/forced backwards which equals maximum pitch. (remembering that the blade is being blown in a wind turbine whereas in a plane it is drawing/pulling).

As I said above though, I like your idea better. Personally I'd try to keep away from steppers, solenoids and other current drawing devices if possible. My interpretation of your drawing and description is that the centre line of the prop blade is offset to the pivot point (the axis on which the blade rotates) which causes a small draw of air (low pitch) during light winds and at high winds the wind forces the prop into high pitch. The prop is mounted to the pie shaped wedge which also turns acting as a swash plate which forces the spring loaded discs together more closely to generate more current. Now that I look more closely at the drawing I don't think that's what you meant but it's how I'd do it. The centre of the blades would be round and fit into a bearing so that adjustable pitch can be acheived. At the centre of the hub a circlip is used to retain blade in bearing. Even more towards the centre is a little cam to actuate disc movement. Unfortunately I can't draw in 3D yet but I'll give it a go in 2D. EDIT Ok it's a very basic drawing showing the cross section of the blade (which is nothing like the shape it should be), the large circle is the bearing and circlip assemblies and the little cam in the middle. Notice that the blade centre and the pivot centre are offset to force blade pitch movement during high winds. Hope you can more or less understand it.

I still wonder however whether it would be better to forget about the variable pitch prop and just use centrifigal counterweights acting directly against the discs (probably at the back end not the prop end) to increase current generation at high winds which equals high rpm? All that is required to match load to wind on the prototype is a few more or a few less washers on the counterweights. Once it's a known factor you just make the counterweights to that weight.

I already knew about pumpinging power back into the grid but I didn't realise that by doing it one can do away with the battery bank which is a major cost saving as well as maintenance time saving.

[skippy]

Here's a quickie of just the centrifigal counterweight mechanism acting upon the discs. Add or subtract washers to adjust weighting. Once again I hope you can understand it.