building a windmill from scratch

[jacquesm]

Hm, I've never kept a diary before, we'll see how it goes !

My name is Jacques Mattheij, I'm currently (and have been for almost two years now) busy with the construction of a 5 m (15ft) variable pitch windmill. We - my wife, son and myself - live in rural Canada and have been off the grid for two years now. Because the solar panels we have are not producing enough power to supply both the house and the workshop we have decided to add a windmill.

The type of windmill I want (>2 Kw, <5 Kw, variable pitch) does not appear to be for sale so I have decided to roll my own.  <P>
So far so good, after all this time I have little bits of results to show for all the effort and a whole pile of 'failures' (or lessons if you prefer to look at it that way).

I started out with buying some magnets from forcefield (1 x .5 x .25 ") and to try to convert various existing 'squirrel cage' motors and car alternators, all with varying degrees of success in making power. Over time the output of the designs has steadily improved and the required RPM's have dropped.

The first time I crossed the 100 W barrier was with an all wooden wheel with a bunch of magnets glued to it and some hand wound coils. About a year ago I built an alternator with 16 1.5 x 1.5 x .375 " magnets and a stator made out of laminations salvaged from an industrial electrical motor. Output was about 4500 watts@540 rpm (powered by the PTO of a farm tractor, the only thing I could think of that would not stall out, I did not have the big lathe then yet), but it cogged like crazy and was very noisy so I decided to do it the right way.

For the next 6 months after that we built - toghether with a dutch friend called Johannes van den Dop - a computer controlled plasmacutter to cut laminations and other parts to our own specifications. A small (scale model) prototype (500 W) was built, but the local winding shop could not get all the copper in there so we ended up with less than the projected power (about 200 W) at 600 rpm. The unit is really small click here for a picture (about 6" across), if I rewound it properly I'm pretty confident it would produce the 600 W that I intended.

6 weeks ago we started the work on 'the real thing'. My objective is to make the whole machine from scratch, without any store bought items other than the unavoidable magnets and bearings. All the rest of it is to be made from raw materials. (well, to a point, I don't make my own copper wire out of ore

The magnets are 18 2x1x.5 " neos, revolving around a 54 slot steel laminated core. I bought a whole pile of them last year, we were joking that anybody ordering any videos during that shipment was going to be pretty disappointed at receiving tapes with nothing but noise on them

The airgap is not optimal, it's a little on the large side, but I was not confident enough with the welder to dare to bring it any closer. Material warp during the welding could easily cause the whole thing to go out of whack. The next rotor I make will be a lot better, and I'll be able to reduce the airgap quite a bit, right now it's about 2.5 mm (a little under 1/8").

I briefly experimented with casting the core in resin loaded with iron powder, but I could not get the flux density high enough to make enough power (about 30% as compared to the steel laminations).

There are two layers of coils, 3 phase wound, so that's 6 x 18 coils two layers thick. Winding the stator was an 'interesting' experience, and I owe a lot to Daniela and Nathan, who helped with the winding until they had blisters.

The machine puts out impressive power, so much so that my 'Meusser' lathe, an old German industrial beast can not push it past 350 RPM without blowing breakers or stalling out (or both). At that point it's making about 3 Kw into a set of 4 12 volt batteries. A picture of the test set up is here.

This whole experience so far has been an interesting mix of going back to school (boy  there is a lot of math in building a windmill!), shop class (the place where I live has an amazing array of craftsmen/women that are willing to spend time with me to teach me their trades, from welding and machining to a friend that came over from the Netherlands to help ironing out some vibration issues in the plasmacutter). Laurence McKay, the owner of 'Norhtern Lights Energy' has been an invaluable resource during this time, he has been building alternative energy systems for the last 20 years or so.

Right now I'm busy writing some software that will help with desiginging the blades (in python) I'll post the code when it's done (not very pretty but it does the job).

The plan is to use the plasmacuttertable with a spinsaw to mill blade blanks (in 3d) out of styrofoam, then fibreglass over that to give strength. We'll see how it goes

When I'm done I intend to post all the cad files and part numbers for bearings so other people can duplicate this without spending the time I did.

Comments and feedback very much appreciated, some pictures of the machine in progress at www.greenbits.com. The governor was a tricky bit to do, I'm not entirely happy with linkage yet (too many wear points there), but right now I want to get the machine finished, I'll revisit the governor when it's winter here.

I'll try to keep this diary up to date, but no promises !

[monte350c]

Hi Jacques,

Looks like a very interesting project you have on the go!

I too have been playing around a bit with foam core blades, and found a really good program that allows you to do several important things.

It lets you compare the lift/drag ratio for lots of different airfoils - XFoil is running in the background.

It lets you easily calculate the all important Reynolds number based on wing chord and airspeed.

If you tell it how long a wing you'd like, the chord at various stations on the taper, and what lightening holes you would like in the templates, the program will generate a full set of templates for your tapered wing. It has an export function to Autocad so you can use a waterjet or laser cutter to make the templates.

All in all a pretty handy program.

The guys website is here: http://www.profili2.com/eng/default.htm

He charges $15 for it and I think it's well worth it!

Looking forward to further updates...

Ted.

[jacquesm]

Hi Ted,

thanks for the link, I checked it out. It seems to be pretty much what I need but it does not run on Linux. I kissed MS goodbye last year - no regrets - and I won't be going back there, but I do have friends that still use windows so I'll give it a try.

Did you use any special coating to stop the foam from desintegrating on contact with the resin ? That seems to be a major problem, as well as getting the top and bottom parts to 'register' properly.

 Jacques

[monte350c]

Hi Jacques,

About the disintegrating foam - I tried lots of different things, and ended up switching to West Systems Epoxy. I found it at a local boat builder's shop. Other than not eating the foam, it's really nice to work with. No smell, (I used it inside the house last winter with no complaints) and the cans come with pumps in them, one pump of resin, to one pump of hardener, so you can just make up the mix as you go along and the ratio is going to be perfect for best strength.

You have a fair amount of time to work with it too, before it starts to harden up. It is pretty much cured after 8 to 10 hours.

You can read about this stuff here at their web: http://www.westsystem.com/

I've just been buying the pink styrofoam at the Home Depot.

My latest trial wings involve using a spade bit in a lathe and boring a hole down the foam for the light steel pipe I'm using for a spar. Then cut the wing with a hotwire between the templates. I'm not sure this is the best way. It might be better to use one of those router prop duplicators mentioned in another recent post here on the board. They don't look too difficult to make either. In any case having the spar in place gives a handy reference to use during cutting since it will be in the same relative place for each blade and hopefully the blades will all end up the same!

I built a vacuum bagging machine for squeezing the foam/epoxy sandwich during cure out of an old frig compressor and a pressure switch off a water pump. If you have a look in my picture files here on the board I think there are some photos of it.

Fun!

Ted.

[jacquesm]

I'm using the 'pink' stuff too, I ran a couple of tests using ordinary epcoxy and ran into the disintegrating foam issue pretty quickly (what a mess). I found that coating the foam with ordinay white wood glue takes care of it but your solution seems much more elegant. (it's hard to hit every spot with something that's nearly transparent). SOmeone else mentioned using polyurehtane foam, but you can't cut that with a hotwire because the fumes that it gives off would be toxic.

Vacuum bagging definitely is the way to go, but I don't have that set up yet (I'll be happy when I have my first blanks, correction I'll be happy if I have a coordinate set for my first blanks...).

I'll dig around for those photos, that could save me a lot of time figuring out how to do that. And time really isn't on my side, it'll be winter pretty soon here.

HOw far does the spar run down the blade ? Do you have problems with the 'changeover' point from spar to no spar in the fibres ? Do you use pigment or do you paint your blades ? Do you use ordinary fibreglass mat (woven) or do you use something exotic ?

I checked out the blade duplicators, I have a 3d 8x4' x6" stepper driven table here, and I was thinking of mounting my spin saw in that. It'll be messy but accuracy should be pretty good that way, and it will be fully auomatic as well as pretty fast.

[monte350c]

Hi Jacques,

The spars are made up of 3 tubes, each one a smaller diameter proceeding towards the tip, so it's got a spar full length.

From a discussion I had with West Systems paint is the best idea to protect the epoxy system from ultraviolet light, which it doesn't like. There are good details on the West Systems web about the type of paint to use. I am using mainly woven fibreglass cloth with strips of mat on the faces to add some strength.

If you pick up a wood shop type cyclone dust collector you can position the suction hose near the cutting head and vaccum up all the cutting chips. Example, have a look at http://www.busybeetools.com/ click the products button and type CT029N into the search box. That will keep all the foam chips under control in a garbage bag. Maybe the chips can be used for insulation...

Ted.

[jacquesm]

Hi Ted,

the dust definitely will be a problem, I did a little trial run with a router and some pink foam, what a mess !

A local canoe builder gave me some pigment, I'll be sure to add a coat of paint to get rid of UV, same colour as the pigment that way scratches won't show.

So, here is what I have come up to date for the blades:

One fairly short (about a foot) section of steel tubing with a 1/4 blade profile section welded on to it, then a 3/4 chunk of laminated teak plywood, then another piece of steel, again welded on to the steel tubing, lots of screws into this one through the steel into the main wooden portion of the root, again laminated out of teak plywood. The steel spar protrudes into this with about 6 ", two bolts go in from the front side through the steel tube and into the wood (further protection against the wood portion of the blade going on unauthorized leave).

The second portion of plywood laminate has 'fingers' routed into it, the reverse of these fingers is routed into the foam, to give more glueing surface and to make sure there are no sharp transitions between 'foam' and 'wood', which would place a lot of stress on the fibres at the transition point.

The fingers are not all equal length, they run 'into' the blade lengthwise (towards the tip from the root), with one fairly long one at the same position as the metal shaft, one much shorter one in front of that and a bunch of progressively shorter ones towards the trailing edge.

I hope that's all clear without a sketch.

The 'wood/foam' composite will be routed as one piece, the two 1/4 steel profiles will be plasma cut and the first piece of plywood will probably be cut using the spinsaw again.

after assembling the whole thing I intend to fibreglass it, I'll get some of the resin you indicated. I have found a fibreglass mat called 'Knytex', it's fairly heavy stuff, has both a woven and a random component. Near the leading edge I'll double up on the fabric

problems looming:

It's very hard to go to '0' using a router in foam, the trailing edge will be a real issue on the second pass.

getting everything to line up for the second round is going to be really hard

I still need to make a vacuum bagging setup

I've never done any of this before

The the three blades will have to be identical, and the blanks will have to be posititioned perfectly on the first pass. I'll probably need to make a set of jigs for the table to make sure I get everything lined up the same as often as I want.