Wind Turbine Transmission

[DanB]

Chris - a couple of comments about your last posting.

Firstly - it's beautiful and thanks for sharing all those pictures, I cannot wait to hear how she runs!

If I were to have any concerns or disagree about anything they would be the following....

- I think the cable to fold the tail is a good idea, something perhaps I should start doing on larger machines.  But I do disagree with your comment about 'not being able to brake a high output 12V turbine'.  These blades you use will be lower rpm w/lots of torque and with your alternator, it may not be able to brake - I don't know, but I've had no issues braking these machines.  Even the 10' turbine (12 Volts, with a 300' line made from AWG 4 wire) had no problem stopping in any wind, until it lost a phase (a connection at the top was poorly done and broke) - then it burned out while 'stopped'.  Normally with the machines we build and the blades we use, we can stop in about any wind by shorting just 1 phase - I often go this route to 'shut down' just because it's a softer shutdown.  That said though, I've never had a mechanical problem from shutting down during high winds/high rpm.

- Where will you put the rectifier?  I worry that the heat sink is too small, especially for a 12V machine - (it's probably fine though we'll see).  I've used 100 amp rectifiers from car alternators and find they overheat at about 10-20 amps sustained output *if* they don't have lots of good airflow through the fins.  When I do use rectifiers off car alternators, I always bolt each half to a much larger heat sink, with heat sink goo etc, and that's worked well for me.  Again though - it's probably fine, time will tell!

I may have missed it here, but it'd be fun to see the power curve (watts/rpm) from this arrangement.

[ChrisOlson]

- I think the cable to fold the tail is a good idea, something perhaps I should start doing on larger machines.  But I do disagree with your comment about 'not being able to brake a high output 12V turbine'.

Hi Dan, I probably should have quantified that and said it depends on the length of the wire run and size wire used.  Most people use too small of wire for 12 volt machines and the resistance in the wire run dissipates enough heat to let them keep running fully braked.  The larger the machine, the worse the problem gets, obviously, but even using 2/0 underground on a 150 foot run I can't stop my 13 foot 12 volt machines from the control panel.  Throwing the safety switch at the base of the tower brings them right to a stop.

- Where will you put the rectifier?  I worry that the heat sink is too small, especially for a 12V machine - (it's probably fine though we'll see).

This turbine is for power in my house so the rectifier is going in a box in the garage so I can use it to heat the garage in the winter time.  No, not really, but it sounds good in theory   

That rectifier shown in the photo is a bit heavier duty than what you've used before.  Each diode in it is rated at 100 amps - they're about as big around as a quarter, and Prestolite rates the whole assembly at 200 amps.  I actually already have that rectifier installed in the panel because my other one with block diodes burned out a few days ago due to a shorted wire.  On the 10 footer, I've seen it put out 40 amps sustained and that rectifier assembly doesn't even get excessively warm to the touch at 40 amps.  On the test stand being driven by my hydraulic motor I pushed the generator to 136 amps for a short while, then backed it down to 80 amps for about an hour and that rectifier still didn't warm enough that you couldn't hang on to it.  It's a pretty big unit - I think heat sink is about 8" long.  The downside is that those rectifiers are about $200 if you have to buy a new one.

I may have missed it here, but it'd be fun to see the power curve (watts/rpm) from this arrangement

I do have those numbers hand written on a piece of paper from when I tested the unit.  I decided that I'm going to put this new machine on the tower today, even though it's only 9 degrees outside.  Maybe this evening when I get a chance I can post the output numbers in a meaningful form like a table or something - I'm sure other folks would be interested in seeing that too.
--
Chris

[JW]

As you guys get into higher power ratings you may consider making your own rectifiers from SCR's and custom heat sinks. The larger SCR's package looks like a bolt with 2 wires comming from them. The triger lead is not used, and the rectifiers made from big SCR's are just as efficent as the pakaged rectifiers that your using.

The image below comes from this link. http://www.allaboutcircuits.com/vol_3/chpt_7/5.html



http://www.google.com/imgres?imgurl=http://upload.ecvv.com/upload/Product/20089/China_Stud_Rectifier_Diode2008941044358.jpg&imgrefurl=http://www.ecvv.com/product/1567509.html&h=570&w=656&sz=29&tbnid=ny1rsIOTMQdHCM:&tbnh=120&tbnw=138&prev=/images%3Fq%3Dstud%2Brectifier&zoom=1&q=stud+rectifier&usg=__RMPyb_zr9ZLKeAdGz1Yx-mc3ydc=&sa=X&ei=uzEOTYf-NcT48AbB2P2yDg&ved=0CCgQ9QEwAQ

do a search for "stud rectifier"

This would be a good route to upgrade rectifiers from what is commonly available. The large SCR's are not very expensive. The bolt part is one connection leg so you may have to configure and isolate each side of the bridges heat sink (use two).

JW

[tanner0441]

Hi

Perhaps you could hire a big wind machine from a movie company and run it through the complete range from cut in to the point of overheat without risking anything.  Or get a big set of blades on the end of the crank on one of those truck engines you work on.

It really is an impressive build though. With the diodes how about oil cooled, it could make a much smaller package, and slower to run away.

As Poco said you must collate the design and build info with all the test results and put it as a book up with the Dan's and Hughe's books.

Brian

[cdog]

This makes me wonder if a water pumping style machine geared up is a good idea, great low wind power, and the blades prevent the machine from running away in big winds?

[fabricator]

Those blades would pump water no doubt, especially if you did a five or six blade rotor, the torque would be incredible.

[cdog]

Sorry fab, I meant a multiple blade, geared up electric mill....

[ChrisOlson]

This geared 12 footer is on the tower and flying.

It wasn't much fun working outside today, but I sold the 10 footer that was on the tower and I have to put that up for the fellow that bought it tomorrow.  So it was today or nothing.  My bride was a real sweetheart and she put on her snowmobile suit and came out and helped me pull the tail crank cable thru the tower, she wired up the generator cables to the stator, helped put the generator and mainshaft shrouds on, and helped me lift the rotor into place to get it on the input shaft.  Our fingers would get cold and we'd run inside and warm up for a bit, then go back to work.  She helped me from start to finish, including helping get the old 10 footer off the tower.  Without her help I don't think I would've been able to get it flying today.  Never got above 12 degrees here today - and that's Fahrenheit, not that goofy metric stuff where water sets up at zero and 12 degrees is balmy.

This machine is a little bit heavier than my other ones so I had to use the skid steer loader to lift the turbine head onto the yaw shaft.

It was too dang cold to take much pictures but I took one of it just after we got it up with the tail still cranked over before I let it go and released the stator brake:



I don't have an anemometer on this tower but the one on the other tower said 15 mph and this thing was putting out right around 40 amps.  The sun was shining bright today so we got lots of power from the solar panels and the batteries were all the way up to 14.7 volts.  So I would calculate its output at ~15 mph to be somewhere around 580 watts.

I have to try to recalibrate my tachometer because the dang thing shows generator rpm now instead of rotor speed.  At 40 amps it said 490 rpm.  Dividing that by the gear ratio gives me about 228 rotor rpm's which means the rotor is running at 6.5 TSR.

So it's running.  Not as much fun getting it on the tower as it was building it though.
--
Chris

[fabricator]

Yee haawww! now we're cookin!

[defed]

Chris, you build these things so dang fast....you've built at least 5 in the time i built 1 4 footer!

i think you should build them, and then sell them cheaply since you enjoy it so much!   

[ChrisOlson]

Well, after sundown the breeze died out and the anemometer on the other tower says 5.2 mph.  The 13 footer that's on that tower is spinning but it's not putting out any power.  This new machine is still putting out 38-40 watts.  So I might have the cut-in a little low on it.

I had a bit of a fiasco with this new turbine yesterday.  And this is one of these deals where you'll see on TV when they say "don't try this at home".

I put the machine on my bracket that I have built for the forklift to test fly turbines on.  I can raise the machine up to about 25 feet off the ground to test it on the forklift.  We had a nice 15-20 mph breeze blowing between the sheds so I took it outside and raised the mast a bit on the lift to get blade clearance.  The turbine swung into the wind and started up.  Before I could get out of the seat it had hit well over 400 rpm and I didn't have anything hooked up to it yet except a little light duty rectifier made of three block diodes hanging off the back of it.

So I uttered some choice words that can't be repeated here, climbed up on the forklift mast, pulled my pliers out of my pocket and was going to short the stator with the plier handle.  Well, the voltage was well over 50.  It's one of those times when you're not thinking clearly because you shouldn't have been doing this in the first place.

After picking myself up off the ground I uttered more choice words that were a lot worse than the first ones, ran into the shop and grabbed some jumper cables.  I managed to hook those up to two phases and get them shorted.  That didn't even slow the rotor down.  So I grabbed on to the generator shaft with my leather glove and tried to brake it.  All that did was put the smoke test to my glove.  That glove got really hot so I ripped that off my hand and threw it in the snow - smoke was coming off it.

So more choice words, I ran back into the shop and found a 10 gauge jumper wire with alligator clips on it.  I hooked that up to the third phase and got all three shorted.  That slowed it down but it burnt the 10 gauge wire off right at the alligator clip and the turbine took off again.

So now I'm getting really pissed and I ran back into the shop again and grabbed the Interstate battery that I had originally intended on hooking up to it and lugged that out there.  Then I ran back in the shop again and got a spool of 10 gauge wire to hook up the rectifiers to the battery.  I had to wire the thing up hot but as soon as I hooked it up it brought the rotor down to a reasonable speed.  Hooking up the jumper cables to two phases stopped it pretty easily then.

So when I got the turbine back into the shop I pulled the rear generator rotor and took a bunch of shims out and tightened up the air gap.  It was at 1.005" and I tightened it up to .870".  So I assume that's why it's still putting out 38-40 watts at 5 mph wind speed, because it shouldn't reach cut-in until 6 mph.
--
Chris

[fabricator]

According to the weatherman here you guys are gonna get hammered by another winter storm starting tomorrow I think, maybe you'll get some real test winds.

[k9]

It is nice to see that some folks are able to think out of the box and are able to build a new wind turbine design and follow all the way through, showing their progress here on the forum. I have been lurking here on the forum for several years, but no body actually came up with something new other than changing cosmetics, mags, diameter trying to boost the output.

It is fresh ideas like this, that make it worth while to come back to and get inspired rather than building the same old thing over and over.

Thanks Chris for posting your project!

k9

[ChrisOlson]

According to the weatherman here you guys are gonna get hammered by another winter storm starting tomorrow I think, maybe you'll get some real test winds.

The forecast says wind up to 20 mph, so it's not what I call "real" wind, but enough to see how it performs in some of the stronger gusts.

I tried to optimize the generator in this new turbine for improved output over a direct drive in the 12-18 mph wind speed range and top it out around 1,200 watts or so.  I'm not interested in peak power.  I'm interested in average wind speed performance.  And as most people know who have built 12 volt turbines, the generator for a direct drive can get quite massive and expensive because it takes multiple-in-hand windings of large wire and usually 16 poles for a machine this size.  This one has little 2 x 1 x .5 N42 bars in it that only cost like $4 each, and less turns of wire than a typical 10 foot 12 volt.

I've been playing with the dual stator generators in my 13 footers for quite awhile, but they're still heavy even though they're only 10" diameter because you have to have two sets of mag rotors with an air gap between the center rotors to prevent flux leakage between the poles.  By the time you get one of those built, with four mag rotors, 48 magnets, and two stators, they're only about 12 lbs lighter than a 16" 16 pole.  And the power curve on them is atrocious.  They're too powerful for a 13 foot rotor and would be more practical on a 16-17 foot machine.  My 13 footers can get those up to about 230 rpm and that's all they do.  But the efficiency is very good and they don't get hot.

So this is a new approach to trying to get 48 volt efficiency from a 12 volt generator using a permanent magnet design, and I fiddled with it until I was getting efficiency numbers between 85 and 90 in that midrange from 12-18 mph.  This ended up being a wye ("star") wound generator because the resistance in a delta unit was just too low and the power curve too steep.

Which reminds me, DanB was wondering about the watts/rpm.  I'll see if I can put that in some meaningful form and post it here.
--
Chris

[12AX7]

Looks great!

ummm...    Did I read "bride" and not wife?

You have a new bride AND have been doing all that work?
I think there might be another book here!

ax7
Mark

[ChrisOlson]

You have a new bride AND have been doing all that work?

Oh, she's not new.  We've been married for many, many years.  But she'll always be my "bride".
--
Chris

[fabricator]

You have a new bride AND have been doing all that work?

Oh, she's not new.  We've been married for many, many years.  But she'll always be my "bride".
--
Chris

OO0h, JEEZ you better hope she don't read that, the "not new" thing I mean

[ChrisOlson]

This is for DanB, and whoever else is interested in it I guess.

When I tested this generator I didn't calculate watts - I wrote down the amps but the voltage was checked and adjusted to exactly 14.5 with the carbon pile in my Sun AVR for each amp reading I took.  Depending on your voltage controller, this may be different.  Some controllers might hold the batteries at "float" at 13.5 and then you'd get less watts.  But at the same generator rpm, the amps would probably go up a bit if the voltage dropped, so it might be a wash.  I don't know.

I had my laser tach on the generator so I'll have to calculate input shaft speed here to make that more meaningful.  The gear ratio is .467:1 overdrive.  Or, for every turn of the input shaft the generator spins 2.14 times.

On the upper readings above 80 amps I only took three or four because the generator started to heat up pretty good.  It's basically good for 80 amps sustained and I ran it at 80 amps for about an hour and the stator got up to about 170 degrees.  So I decided that was the max upper continuous limit, even though it will handle spikes up to 135-140 amps.

Also, all the amp readings were taken using a single piece of 10 AWG wire to connect each stator phase to the positive and negative diodes for each phase.  On the tower this machine has two 8 AWG wires from the stator to the base junction, but those wires are 54 feet long.  So, even though I didn't actually figure out the ohms, I figured the 10 AWG gave a reasonable simulation of resistance in the wire run.  The 10 AWG got warm but it didn't discolor or burn when I was testing it.

Now, I'm going to see if I can make a table here to put this in.........

Generator RPM	Rotor RPM	Amps	Watts
212	99	.5	7
236	110	4.0	58
263	123	8.9	129
319	149	19.1	277
371	173	28.6	415
420	196	37.4	542
464	217	45.4	658
505	236	52.7	764
542	253	59.3	860
575	268	65.1	944
604	282	70.2	1,018
629	294	74.6	1,082
650	304	78.2	1,134
677	316	83.3	1,208
731	341	93.6	1,357
800	373	106.4	1,543
955	446	135.8	1,970

Hope all the above gibberish turns out OK on the board.
--
Chris

[Dave B]

I had a bit of a fiasco with this new turbine yesterday.  And this is one of these deals where you'll see on TV when they say "don't try this at home".

Chris,

  I hope you aren't to brusied and battered from your event yesterday, I also know how fast things can happen once those blades start to fly. It's great to see the machine on the tower now and I am quite certain there will be times when you will be glad you have the manual control of the tail. There was more than one time before I had either the manual brake and or manual tail crank that I could not stop it and or keep it from starting even shorted. I had visions of shooting a leader wire with an arrow up 85' plus and over the blades pulling some kind of rope or what ever to jam things up. My next machine or this one modified will again have a manual brake (much ,much more heavy duty and probably disk) as well as the manual crank for the tail that I will never put one up again without. We're glad it sounds like you are OK, like many here on the board we are looking forward to your future posts with this project.  Dave B.

[ChrisOlson]

 I hope you aren't to brusied and battered from your event yesterday, I also know how fast things can happen once those blades start to fly

Well, I learned a lot from that test and I'm glad I actually did it.  I might have had the rotor running too fast with the air gap where I had it.  It's safer with the air gap tightened up a bit until I get a handle on where those blades like to run.  This geared unit gives me a pretty wide range of performance options to match the rotor, from swapping the gen rotors out with wedge mags to make it "tighter", to running just one mag rotor with a "core" rotor with no magnets on it to make it "looser".  With a direct drive you're kind of stuck with what you got, outside of making an air gap adjustment.  Because the generator spins so fast on this machine, any of the above options will work and I can change the rpm/volt +/- 8 either way from where it is now and it will still work without changing the rotor rpm considerably for cut-in.

I was always a bit unsure of blades with no twist or taper in them.  I'm not anymore after that "test".  I found out those blades have absolutely no problem lighting right up and running well over 11 TSR with no load.  I should've realized that in the first place, because anybody who's ever seen an old Wincharger run (I have) hasn't really seen a turbine turn serious rpm's until you've seen one of those.  And when those cups come out on those things at about 35 mph wind speed it sounds like somebody opened fire with a M60.

Getting around 40 amps today when I got it flying was about the range I was shooting for at 14-15 mph wind speed.  That's about 4-5 more amps than my 13 footer makes at that same wind speed.

On the tail crank comment, I think you're absolutely right.  Every one of my turbines from now on are going to have it.  Once you have a runaway a mechanical brake is about useless unless it's a pretty powerful unit, and able to handle the heat.  Even a 12 footer can make 5.5-6 hp at the shaft.  You think about putting a mechanical brake on a 5 hp electric motor and trying to stop it.  It takes one hell of a brake to do that.  Cranking the tail is the only real safe way to get a runaway rotor under control, and it's about the only dead reliable way that you know without any doubt, is going to work.
--
Chris

[Harold in CR]

 Job well done. Congrats.

 You documented this build as well and as simply as anyone could possibly do.

 

[wildbill]

chris, i would like to meet you. i live just north of spooner. i take it you are in a farming business? but i can't beleave you forgot 101 of farming, you never put any clothing next to a moving shaft(glove) i know you were in a panic,right? i really like your postings.

[ChrisOlson]

chris, i would like to meet you. i live just north of spooner. i take it you are in a farming business? but i can't beleave you forgot 101 of farming, you never put any clothing next to a moving shaft(glove) i know you were in a panic,right? i really like your postings.

Hey, that would be cool!  You're only about 35 miles from me.  Email me - my address is in my profile.

Yeah, that's why if you saw that on TV they'd say "this is done by professionals that do stupid stuff - don't try this at home".
--
Chris

[TomW]

The glove on shaft brake is an even older version of the hand brake old cars had, eh?

I just got that bit stuck in my head.

Nice stuff. Very nice to see some variations on the home built turbine theme. In case I didn't say so before.

I, personally, think it might be an interesting angle to put on a seminar / workshop / tour during the "down time" of winter farming. After all the repairs are done to machinery anyway. If that ever gets done? If you are into that kind of thing, anyway.

I am close enough (50 miles SE of La Crosse )I would attend such a thing should you do it. Even help get it rolling.

I am no builder just an armchair wannabe. 

Just thinking into the keyboard.

Anyway.

Thanks again for the share.

Tom

[ChrisOlson]

Here's the final conclusion to a turbine building project - the new machine running on the tower.  Just a short video - it's still quite cold here today:
http://www.youtube.com/user/OlsonFarms?feature=mhum#p/u/6/P9Vs0e11VIs

It got down to 7 below here last night and no wind at all so the machine quit running overnight.  It started up this morning at between 3-5 mph wind speed - it was hard to nail down exactly what it takes to get it turning.  But cut-in is right around 5 mph, which is a little low.  I got a Doc Wattson inline on it to take instantaneous wattage readings compared to the anemometer, and this is what I got so far.  I can only use the Doc Wattson up to about 50 amps continuous, so it will have to come out of the line when the wind picks up.

7 mph - 71 watts
10 mph - 259 watts
12 mph - 392 watts

So that's about it for this project.  Really fun one.  Hope you guys enjoyed it as much as I did.  The wind is supposed to pick up more later today and hopefully I can get a power curve on this thing up to about 20 mph or so - and learn new things from it.

My wife and I are leaving for the holidays in a couple days, so Merry Christmas and Happy New Year to everyone on the board!
--
Chris

[cdog]

Just an awesome job, Merry Christmas!!

[DanB]

Cranking the tail is the only real safe way to get a runaway rotor under control, and it's about the only dead reliable way that you know without any doubt, is going to work.

The best way I think (and perhaps you've done this) is have it such that by default, the tail will be folded up (like a Jake) - and the winch is required to unfold the tail.  (this could be tricky with a furling machine though)

And  - as one who has never done a brake, or a tail that folds up with a winch ... I should not be saying anything!  However - it is not dead reliable.  Blades like to seek the wind, I have seen machines (Bergeys) with the tail completely folded up via the winch (supposed to be shut down), track the wind perfectly and 'run away' ~ kind of spooky stuff especially with a 23' turbine, but the Bergey is tough enough to hold up to that.  Folding the tail is some insurance, but it's not 'dead reliable'.  Given my choice, I suppose I would rely on shorting the alternator first, and if a backup should be required then a brake is probably good way to go, and to be 'sure' - the default mode should be 'stop' and cranking the winch should allow it to 'go'.

[ChrisOlson]

Folding the tail is some insurance, but it's not 'dead reliable'.

But yet you consider it a pretty much dead reliable way of controlling power output?

Folding the tail reduces the rotor's swept area drastically.  If you lose the generator or geartrain and the machine is free-wheeling in high winds I'll take folding the tail to a brake any day on a fixed pitch machine.  I don't really care if it "seeks the wind" at that point because it won't seek it to the point where you have a tower strike or blade failure.  It may keep spinning, which is perfectly fine, but with the tail folded it stays under the structural limits of the rotor, and that's what it's all about.  I've flown machines in winds close to 100 mph, and once you do that you reach the realization as long as the generator stays working it's fine.  If that generator goes you may as well retreat to a safe distance, have a beer and just watch.

If you calculate the amount of power flowing thru that rotor at even 50-60 mph, a larger rotor can start up, come out of stall and fly with the generator fully shorted.  You may have never seen it, but I have and the best thing to do at that point is to just release it, let it fly and hope the furling works.  With the tail folded you won't have that problem.

To my way of thinking a brake is only useful on a turbine to keep it parked in high winds.  On a geared unit you'd have to use a brake on the low speed shaft, and then you're dealing with tremendous torque, which would take a very big and powerful brake, which adds considerable weight to the machine.

As far as which is default - "go" or "stop" on the winch position - that would get really tricky on a furling machine if the default was "stop".
--
Chris

[DanB]

Hi Chris - yes, furling works pretty well to control a machine thats under load...
it's when the load goes away  - or becomes reduced (blown rectifiers - broken connections etc) that the machines start furling late - or not at all.  So I've observed 'unloaded' machines that both fail to furl - and - in the case of a 10kW bergey I've seen, track the wind perfectly even though the tail was completely folded up.

And all this said - again - for the most part, folding up the tail is a common solution and it does work well.  It's just not 100% is my point...  I think it's fine and wonderful though, and I think that new machine you've built is fantastic.

[ChrisOlson]

Hi Chris - yes, furling works pretty well to control a machine thats under load...

Amazingly, these GOE222 blades I got seem to furl fine with no load.  I had to take the Doc Wattson out of the line because the wind picked up pretty good and when I did that it unloaded the machine.  I decided this would be a good chance to see what cranking the tail does to it in moderate wind.  I went out to the tower and looked up - and it was running almost furled!  Didn't even have to crank the tail.

I went back in the house and hooked up the cables from the rectifier to the battery bank.  It had a short surge to about 120 amps, then went down to about 70 amps.  So I went back outside and looked and it had straightened right back out and gone back to work.

First time I ever seen that happen.

I cranked the tail with it loaded and it didn't stop it but it kept putting out about 8 amps turning pretty slow.  I uncranked the tail and let it spin up again, then threw the GE safety switch at the base of the tower and it brought it to a gentle stop, then kept windmilling at a slow speed.

I'm tickled pink with this machine.  The midrange wind performance is pretty impressive even though I got the cut-in set too low on it.  I've yet to see it furl under load, although it does start to furl at about 70 amps and I seen the tail at about 45 degrees once at 80 amps.  It was supposed to be fully furled at 80 so I got the tail return spring set a little tight and I'll have to move it in one hole.

But other than that, I'm VERY happy with how this machine is running.  I'm sold on geared turbines.  I'm going to build another one.  Except on the next one I'm going to make up some 2D CAD drawings of the transmission case halves and have them waterjet cut at AyresTech in Rice Lake.  That will save me a lot of time on the mill, milling holes in those transmission case halves.
--
Chris

[12AX7]

Hi Chris..

It looks very good to me! 
Now for the rude/ugly questions

Any idea what is the total number of hours and how much pocket change ?

You have any idea how many of us are jealous ... and by how much?

Nice!

ax7
Mark

[ChrisOlson]

Any idea what is the total number of hours and how much pocket change ?

Well, the transmission has about $65 worth of extra parts in it that a direct drive don't have - namely an extra shaft, two extra bearings, two sprockets and the drive chain.  The rest of it is pretty much a wash because you still have to have one set of bearings, stator support and on and on to build a turbine anyway.

Being the case is integral with the yaw tube and tail mount, it's just basically 5 pieces of sheet steel torched out of a sheet of 1/4" and all welded together to make the case.  The cover is made out of a piece of 3/16" sheet steel.

The generator has roughly half the wire in it that a direct drive would have, and 24 2 x 1 x .5 N42 bar magnets instead of 32 2 x .5 disc magnets.  I figured the savings in magnets alone at about $175, depending on where you get them from.  The generator rotors are 10" diameter instead of 16".  And the stator is 14" OD instead of 20", and only .450" thick instead of 5/8".  You can get away with the very thin stator because the diameter is small enough that it won't warp and come into contact with the rotating assembly when you start applying serious torque to the mount.

It cools better because it has less wire mass to retain heat, is thinner, and because the generator rotors are spinning at such high speed without the magnets being encased in resin, the rotors become centrifugal fans.  Those rotors move a LOT of air over that stator at 600 rpm.  I had absolutely no overheat problems testing on the stand at 80 amps for an hour because if you tape a piece of paper to the outside perimeter of the stator that paper stands right out on end from the air blowing over the stator.

So there's a number of advantages that I see here.

I never figured any of the costs to the penny, but it was cheaper to build this geared unit than it would have been to build a direct drive, with most of that cost being in the generator.  The downside is that it takes more work and some basic machining to build it.  At the minimum, unless you get your parts waterjet or plaz cut, you'll need a lathe, vertical mill and drill press to build one.  I have all that stuff, but if you had to hire it done, then the cost would go up because machine work does not come cheap.
--
Chris

[windy]

ChrisOlson.
 Thanks for taking the time to post your story. I am really interested in your design of the furling system. I have used the gravity furling system on both a 10 footer and on my 16 footer and and both windmills act the same. The wind here is quite variable and when it gets above 14 or 15 MPH the tail starts to furl the windmill in and out of the wind. I am heating water using a 48 volt battery bank with all excess power going to the water heater using the Tristar-60 controller, and when it starts to fully furl, the blade slows done, amps drop from 50 to 10 amps. The blades then swing back into the wind, and the whole process starts all over again. It will keep doing this until the wind drops down to around 18 MPH. I was getting peaks of 30 amps, so I increased the tail hinge angle, which increased amps to 50, but that only made the tail movements worse. After seeing your breakaway idea on the tail, I thought that this may be an idea I may try. But instead of a spring, I was thinking of using two neodymium magnets positioned in such a way that at the moment of maximum amps the magnets would separate and the tail would fold back and would stay there until the wind slows down. Using this idea, the windmill would not have to constantly furl back and forth. I can change the tail hinge angle anywhere from 3 degrees to 20 degrees so I could still get it to furl back to the magnets after the wind slows down without using a spring.
 I suppose if I had an inverter drawing power out of the batteries, the generator may not swing so much. As you stated, its't too cold to do anything with it this week. I live just west of Minneapolis, and do family campouts during the summer down by Baraboo,which doesn't sound too far from you. Would be interesting to stop by and look at how you set everything up.

windy