Semi-Invisible Downwind mini-turbine

[CmeBREW]

Hello RE-group,

      My latest crazy mini-mill project is something I have been meaning to do for a long time-- to make a small mill that is practically invisible even if it only makes low, consistent power in a low turbulant location.  (goal is 20-30watts max)

I do not know the power yet--still waiting on some decent wind. If it works decent, I will call it the 'INVISI 32X Downwind turbine'.

The blades are made out of very tough Polycarbonate. It is totally different from that brittle plexyglass.  This stuff I couldn't even break with a hammer or snap it. They make tractor shields and machine guards out of this type of polycarbonate Lexan. It machines easy too.  All's I could get was the 3/16" thick, so the blades are a little heavier than I would like at 1.4 lbs each.

The rotor with blades is 32 inch diameter.  Not much swept area I know, but at least it is silent and not noticable.  

Here is the first video with it going slow in a little breeze (I am standing on the peak of my roof):

http://www.youtube.com/watch?v=Wh3z2Efj4Jc

Sorry for the wind noise-- I forgot to put on the filter.  I sound bummed out STILL waiting for some decent wind for days!!

Here is one more video with a little more wind-- feels about like 10mph but still to slow. The treadmill motor was just barely reaching a 6v cut-in (actually about 8v)making a couple watts so far.(probably only around 240rpm)

I need more wind!

http://www.youtube.com/watch?v=ykKVaVDAoZE&feature=related

The treadmill motor is only temporary while I finish the small alternator.  I needed to see the rpm and behaviors of these flat blades  before I can get any rough idea of the coils I need to make for the stator. The mag rotors are already done. (its a 8/6 dual mag rotor alternator)

So far, the blades SEEM to be somewhat slower than I had hoped, but they do have quite a bit of torque feels like.

For the testing of these round slower high solidity blades, I just screwed them to treated plywood with screws and used nuts to angle the blades.  The blades look to be around 7 degree angle, but its difficult to be precise. If the project works out, I can weld up steel brackets instead of plywood and it should be even more invisible.

I'm not sure the static balance is perfect either. The oval shape makes it difficult.

I wonder now if a semetrical elongated round shape would be easier to be more certain of perfect static balance.

One good thing about these slower, high solidity blades is they turn (YAW) this DOWNWIND mill very effectively into the new wind direction when stopped. (Unlike my last Downwind mill)

The big blades gets over the motor cogging easily even with the small diameter.

I have no idea what it will do in very high winds since there is no furling. I hope it holds itself back. If it don't -- I can kiss the blades good bye since the high resistance motor will not hold it back by shorting.  We'll see.

I will soon see just how fast it can go-- and if it holds together. I hope it will go up to 600rpm without shaking or becoming violent. I realize these small mills are just as dangerous as the big ones, so I will certainly be far away believe you me.

I believe I can also possibly bend the polycarbonate blades with a wood form and my heatgun into a graceful curve shape to reduce drag in the back side. (if I understand that correctly)

But I am not sure how much better that would increase the speed and power though.

Anyway I think it looks really neat and it is exciting to try to make the first almost invisible windmill.

I will post again if and when I get some power readings and when I make improvements.

Any comments, questions, or constructive advice would be much appreciated.

-Thanks!

[zap]

Nice!

Now all you need is an invisible hub and tower.  It's almost impossible to complain about... and steal... something you can't see!

[Dave B]

Pretty neat idea. If you made the hub mount round it would appear even less distractive as you would not see the interferrence of the blade mounts. It would appear as a solid circle even when turning.  Dave B.

[coldspot]

"bend the polycarbonate blades with a wood form and my heat gun"

 My $0.02

Looks like you could maybe turn the blades

1/4 turn and get a bit more span, (longer).

 Then you would get a bit more power maybe?

That is if you are going to be heating and bending.

Again, just my $0.02

 nice work

[Ungrounded Lightning Rod]

Looks like a dandy bird-chopper.

I'd use a ducted fan arrangement:  Put a ring around the outside of the blades.  (It's OK to fasten the ends of the blades to it and have it turn with them.)  You should gain more power from blocking air doing an end-run around the blades and depowering the tips than you lose from air friction of the duct against the wind.

Tip-depowering would usually be fixed by bringing the tips to a sharp edge.  But that turns it into a set of swinging invisible knives when the blades are transparent.  A spinning duct will give the birds something to bounce off if they approach from the side.

Not sure what to do about birds approaching from the front.  Maybe make the space between the blades large enough that some of them make it through rather than being hit.

(I've considered a transparent Savonius as an eyesore-minimizer.  Birds might be able to go through that pretty well since the only place they'd hit an edge it would be moving away from them at about 4/5 the wind speed, though I'm not sure about the flats...  Thanks for mentioning polycarbonate.)

[CmeBREW]

Thanks for the suggestions.

     The mill turned quite a lot today but still only 200-300rpm. The flat blades are just not fast enough. I've never tried flat blades before.  That drag is a real pain. If I wanted, I could get something out of this way, but I will try instead to bend the blades into a slight curve to get some more speed.

     With these slow blades, I highly doubt it would ever kill a bird.  I have never seen even one bird killed or even hit by ANY of my mills and they turn so fast you can't see them.  But As you see in the video you can still see it turning, especially the center part.

 The blades have varriing angles, so they reflect the sun when they spin to some degree. It is far more visible than the normal high speed 3 thin blade turbines actually.

My last 3 footer was going over 1000rpm a lot and to human eyes was invisible, but this poly mill is going WAY slower, usually under 300rpm and is still quite visible while spinning.  

     But like ULR comments on this (bird) consideration, I see now it would be impossible to convince others (esp. bird lovers) that this does not kill birds due to the clear blades.  I actually never even thought about that.

That is funny, because the whole reason for this design is to try to 'PLEASE thy Neihbors' (to be less noticable), but if even one bird loving person on my street believes it can kill birds, then I will have to take it down.  Boy, you just can't win!

If it actually killed even one bird, I would take it down. I love birds. (except for startlings, crows, and sea gulls)

I'm not even sure now if I can get any more speed from it. If I can't get at least a couple hundred more rpm's, then it is probably not even worth it as a mill.

I've got doubts, but I will try one more thing.

-Thanks.

 

[hamitduk]

Just remind your neighbors about Darwin's theory, there is a good chance that the dead one should have been pulled out of the Gene pool. If there is still a problem, front the cost for them to take flying lesions.

Hami

[dnix71]

You need the tubes used in bank drive throughs to make the support pole, or this stuff:

http://beverlytang.com/archives/materials/transparent_aluminum.html

Transparent aluminum that is stronger than steel.

You could make the hub out of it, too. Then you would have a real back yard bird Cuisinart.

[ghurd]

I thought that was only a StarTrek thing!

http://memory-alpha.org/en/wiki/Transparent_aluminum

G-

[CmeBREW]

Thanks guys-- Actually, I don't want to spend too much on this project.

I did make a change that helped a lot.  I increased the angle of the blades even further using 3 angled wood blocks as seen in the photo here:

The blade angle may be 10-12 degrees now.  The angle block(s) goes 1" high.

It has even more torque.  It also clearly goes faster now and makes 2-10 watts (into 6v batt) very consistently and so far has went up to 20 watts several times.  But it will not go fast enough for 12v batts because of the treadmill motor.

I doubt the idea of bending the polycarbonate with a heatgun will work right. I did a small test piece and it was difficult. It didn't bend until it melted it at a point and it wasn't evenly bent into a curve as it was clamped to the wood form.

This small high solidity mill actually did more consistent power than my last 3' diam mini-mill project with 6 thin pvc blades that was tested on this same pole/tower location in similar winds.  

I still need to replace the wood screws with bolts to make certain these heavier oval blades won't fall off in a big wind gust.  That could be very unsafe. But It is in a safe location.

It has been an interesting project. It starts up very easily and it turns into the wind directions from a dead stop very nicely.  It has been perfectly silent so far which is nice.  However, there is a good chance it will need some kind of furling.  I will find out tomorrow in the 20-30mph winds. I hope it won't, but I now have serious doubts the wide blades will self- limit the speed.

Here are a couple more little videos showing that the blades can still be slightly seen even when going at near it's top speed. You can see how it even reflects some light.

http://www.youtube.com/watch?v=wMtmg_h6Gt8

I wish I hadn't used the word 'Invisible' for obvious reasons now. It is not invisible.

It is just LESS NOTICABLE when spinning slow or when completely stopped than a typical small mill.  That was the whole idea.

One cool thing it does at nighttime in the dark is reflect light from a distant light pole hundreds of yards away, and it looks like a flickering LED wand moving above my roof.  I almost feel like disco dancing!

Sorry this video is sideways. I must have been holding the camera vertically?? (Just turn your head or monitor sideways)

http://www.youtube.com/watch?v=JzQDKIymPaM

I am hoping that the lower rpm alternator I am still making now will allow it to do even more power, but into 12v batts.  But even now it is a pretty neat little 6v batt charger on my turbulant roof.  I then easily switch my two 6v batts in series to 12v to use with my small TV.

 I will keep messing with it.   -Thanks.

[CmeBREW]

OK, Here is what happened with this little experimental poly-mill in high winds with no furling.  It did quite well actually.

 Last night had some bad thunderstorms most of the night.  Wind gusts probably up to 45mph. Best thing I noticed right off is it makes no noise even on this pole attached to my house with me sleeping practically right underneath it. (about 10 feet away)

Of course, I have the mount suspended with foam rubber pieces for good isolation from the vibrations.  You couldn't sleep without it.

Today was very windy all day 20-30mph.  But up on my roof it is very turbulant and probably not quite that good.  Into my 6v batts it is doing a lot of 20-32 watts with the bigger gusts.  Last night it probably did upto 40 watts.

Here is the video I made a few minutes ago.  Notice the mill tracking the turbulant wind directions very well.  It actually turns even much more with the terrible turbulance than the video shows: (Sorry about the wind noise again-- I learned this camera has no foam audio filter, so I tried a tissue holding over the mic, but didnt do so good anyway)

http://www.youtube.com/watch?v=pDJt8gIlRhs

I also did testing with it into my 12v batts since the winds are so strong today.  It is strange, but even though it spins faster, the max power looks to be the SAME as with the 6v batts.  Probably because of the slower high solidity straight blades.  Into 6v would do more consistent Watthours anyway. Also, I would rather have it spinning slower anyway , so I left it hooked to the 6v batts, and since the mill can only charge 6v batts in lower 10-20mph winds anyway.

I actually have to stop my 5 foot hawt when it is this windy. But I get to keep this little one going non-stop  which helps fill my batt needs good enough.  I don't think I will mess with furling for this small Poly-mill. I doubt turning 30 degrees out of the wind would do much of anything anyway. So probably not worth the effort.

It's been fun.   -Thanks.

[TheCasualTraveler]

     I couldn't see clearly in the photos. Can you detail how it was mounted to the pole for downwind, the yaw bearing?

     Neat mill.

[CmeBREW]

Thanks CasualTravler,

   It is the good ol' pipe in a pipe ploy. You can see the up close pics here from the old 3-blade (Passing Wind) way I use to have it:

http://www.fieldlines.com/story/2007/3/8/31258/26067

Even though it was my very first mill and I was excited about it, I soon realized it had some problems.  The biggest was the noise outside AND the vibration sounds from it on the inside.  I lost many a night's sleep I can tell you!!  (But now now)

It also had problems yawing into the new wind direction the following day. Many times the wind would start up in the exact opposite direction the next day, and I would have to turn it often with an extention pole. I got tired of that.  And it had a problem getting over the cogging of the motor.

Yes, 'Passing Wind' (original formula)  has gone with the winds.

I thought about calling this new (version) Poly mill something like "Passing-Poly-Wind 32X" , but I decided on something with a little more class in case it actually worked decent.  The only thing different is the new Poly blades and hub. But I couldn't get the flimsy cheap 75' long extention cord INSIDE the pipe!! Wasted 45min trying.  So it just wraps around the pole for now.

I hope it holds together, we are getting scarey strong winds all of a sudden now(50mph) and I didn't get a chance to put the stronger Bolts for the blades on yet. Hope it holds together-- It is going a lot faster than the video Now!! (40Watts+ now--yip'ee!)  

-Thanks.

[CmeBREW]

I forgot to mention above that the two big "Washers" I used inbetween the yaw pipe are actually not washers but are called "Machine Bushings" that I bought at 'Tractor Supply Co. /TSC'.  The are back with the tractor parts. They have different sizes which makes it easy.

The Poly-Mill successfully made it thru some VERY strong winds all day and especially last night.  Last night I tested it in these very big winds into my 12v batts again, and it now sure looks like it DOES self-regulate the speed of the blades in big winds and 50mph gusts.

And it makes absolutely NO sound at all during these big winds.  That was the problem with the old 'Passing Wind' Mill,  it was fairly quiet until the really big winds came around and after about 40mph wind gusts I could not control it and it really made a bad aeroplane noise that I'm sure my closest neihbor could hear at night time especially.  So Now I only want mills that make No noise.

But with this small Poly-mill, It sure seems that the blades can only go so fast in a very big wind gust because it actually does more max power into the 6v batts than the 12v batts during this high wind testing.  The max into 12v was only about 30watts, but the max into 6v batts was almost 40watts.

I went up to inspect it closely today after the big winds went away, and as I feared some of the wood screws were starting to coming loose from all the high wind abuse.

The blades were no doubt pushing back and forth hard all night.  So I will mount the blades with all bolts ASAP (instead of wood screws) as I had stated above.

I really do believe I can get a lot more power from this small mill if I can make and match the right slower alternator to it.  For straight big wide blades, it goes faster than I thougt it would.  It sure seems like a lot of torque.  My quess is it is going over 600rpm for sure.

But If I believe the forecast is for mega strong winds above 50mph, I will just tie the mill rotor down with a rope like I do with my 5 footer when tropical storm winds come around.  

I will keep trying to get more power out of it.

-Thanks.