The learning curve.

[ksouers]

Well, it’s been an interesting couple of weeks. I don’t yet have all the parts I need build my first alternator but I thought I should at least get some experience building a turbine. To that end I dug around in one of the many junk drawers and pulled out a couple motors I managed to liberate from an ink jet printer picked up at a garage sale a couple years ago.

Spinning this motor in the lathe only gets 7-8 volts at 2000 rpm. I know, that’s “not useful” for anything. Except yes, it is useful for learning, as long that knowledge doesn’t require a specific voltage. Then whatever voltage you get simply becomes a reference, a metric, if you will.

In this instance the fundamentals of turbine operations and design is the knowledge sought. The mechanics of how things work, and what doesn’t, is what I need. Sorry, I didn’t get any pictures. At least not yet, the learning is still ongoing. The first iterations have been quite ugly. Extremely so.

I used structural foam for the blades. You know, the pink stuff you get at Home Despot and such. I used the most basic airfoil I know, the Kline-Fogelmann. It’s used extensively in scratch built model RC planes, as is the foam. The airfoil has nice low speed characteristics making it great for the foam airplanes. It’s also very easy to make, since it is basically a slab with a step in it, make your base from one piece of foam then hot glue another piece on top that has about 2/3 less chord. Shape it a bit and you’re done. I can make a set of blade in about 15 minutes like this.

So, what exactly did I learn? Lot’s of stuff. Nothing empirical but, then, it was subjective data that I was after anyway.

1)   Twist is very important. I knew that from the beginning but had to start out with straight slab blades to find out just how important it is. Do not underestimate it.
2)   Mass always wins. One of my own sayings I’ve used for years. It stays true even with wind turbines. The light foam blades start and stop quickly. Mass needs to be added to perform smoothly.
3)   Match the blades to the generator. Yeah, I learned that from you guys. I made long and short blades. Short worked best with the small motor.
4)   Someone else said it best: “The wind doesn’t blow here, it sucks!” Sorry, I don’t remember who. But it’s very true. I knew this was a lousy wind site. I just didn’t know how bad. I do now. Because of all the buildings and trees there is much turbulence and wind changes direction constantly. The turbine will blast alone for a second or two putting out a couple volts then abruptly stop. Or it may swing wildly, usually within about 120 degree arc but I’ve seen 180 degrees or more frequently. Usually it seems like its doing a three at once.

The education will continue. I have lot's of things I want to try, and to learn.

Kevin

[ghurd]

Big fun in little packages!
G-
(Woof said your quote)

[JeffD]

Yes, the never ending learning curve, but it is fun, most of the time.

Glad to see some one else trying the KF airfoil.  I started experimenting with it in October 2009 and in Jan 2010 changed all of my little turbines to using the KFM3.

[ksouers]

ghurd: Yes, it is. Thanks for attributing the quote. Sorry Woof.

Jeff: I've been using the KFM2, I may try the KFM3. The blades could use the extra stiffness, I've had several tower strikes with the gusty winds we have here bending the blades back. What did you use to make the KFM3 blades?

[ghurd]

If you want something "useful", try a stepper motor (also from printers).
Can charge AA ni-cads/Ni-Mhs, and everybody needs their AAs recharged.
I had some nice pics from a couple people of such projects.  Lost with a 'puter crash.

Yards with trees and buildings, and a 6' tower, usually have somewhere the wind is less turbulent.
Mine has 3 places.  Can't see the best place from inside the house, so I can't leave one there.
The other 2 places have a wind tunnel effect due to the wind being guided between houses and trees.

Turbulence will cause the blades to very quickly nearly stop, even with wood blades.  I don't think heavier blades will help a lot.

Did you see my ruler blades?
I think I will call them "GHm1".  LOL
http://www.otherpower.com/toymill.html#glenh

G-

[JeffD]

I carve the KFM3 blades out of well seasoned wood: scrap spruce lumber from the land fill  .

I also live in a well built up suburban area  and had big problems with turbulence.  Finding the sweet spots for my little turbines did take some time.  In 2008 I placed several home made anemometers around the yard to try and find the sweet spots.  Each anemometer was attached to a cheap bike computer in order to record rpm stats.  I lucked out when Canadian Tire put the Schwinn bike computer on sale for $5.99 so I picked up five of them.

I tried the heavier blade route.  They do take longer to run down but also take longer to run up to speed.  I try to make them as light as possible but keep them stiff.  I found that the bearings play the biggest role in keeping the turbine spinning in low speed turbulent winds.  Crappy blades with low friction bearings work better than good blades with high friction bearings.

[ksouers]

Thanks ghurd. I suppose I should have mentioned I had the turbine mounted on a 15 foot "test" tower. The tower gets the turbine above the garage but I still have the very tall trees. I have sort of the wind tunnel effect you describe but only if the wind is from due West, but still affected by tall trees in my front yard and houses across the street. It's just a lousy site all around.

I want to put a taller tower out behind the garage with a permanent footing. I can go to about 20 feet without drawing undue attention to myself.

Then again, my wife and I have been looking at buying another house for the past year. I want greater than 5 acres anyway, I don't like post stamp lots or subdivisions. We only settled for this place because we were in a hurry at the time, it was close to hospitals and doctors. A suitable site for wind and solar is a big plus. It's getting a little awkward to find something we both like.

Yes, I've seen the ruler blades. While I was digging around for a motor I came up with an old 5 1/4 inch floppy drive that has a "pancake" motor similar to the one in that article. Unfortunately it's the "bad" kind, but I plan to heavily modify it (already started) with dual rotors, just to see what it'll do.

Jeff: The foam blades are just too light. Almost no mass at all, so a couple small washers on the tips really do help.  I used dowel rods to stiffen up the blades, started out with poplar but that was still too flexible. I switched to oak which helped a lot and added mass.  Shortening the blades helped a lot too. I now get more RPM. It’s just going to take some tweaking to find that sweet spot.

I only have the area in front of and behind the garage. Everywhere else has overhead obstructions. Yes, It’s a shady yard ?


Thanks,

Kevin

[ksouers]

Snagged a couple pictures with the cell phone when I got home. These are the small (14 inch) blades.
This is the pancake motor, got it flying yesterday just to see it run. Still have to make some mods to it though I have replaced the ceramic ring magnet with a bunch of the little disk magnets from Harbor Freight. Puts out about .25 volts in a very mild breeze, I did see about 3.5 volts in a very strong gust yesterday just before the 18 inch blades destroyed themselves on the tower.



You can see some of the trees that surround me.

[ghurd]

"The bad kind" of motor.
Eddy currents in the iron plate make it act like a brake, and drag down the RPM.

If you can get the coils off the iron plate undamaged, should be a neat little experiment.

I did get a few sets off undamaged (some come off easier than others), but never persued it to the point of assembly.
I suppose with the right motor, could replace the iron plate with perf board, and even use the same bearing assemblies?
G-

[ksouers]

That's the great thing about this motor, ghurd.
The coils are on perfboard, though the board is very fragile.
The iron parts are completely separate so it's a good candidate for modding.
I have to make a spacer to get the rotor away from the board, but that's not a big deal. Just a little sliver of aluminum. And I will have to redrill and tap the screw holes.


Kevin

[ghurd]

I gotta find one of those motors!

Fragile might not be such a big deal?
Consider a healthy "gooping" of JBWeld on the coil side?  It should make it a bit more robust without increasing thickness (air gap).

Remember, the coil board may have components that could mess up the works.
Remove the parts and cut the traces (in many places), just in case.

Spacer may be best made of plastic?  A few layers of 2-liter soda bottle plastic?
Depends on the overall layout, but something 'plastic' would be what I would try.

Whatever you decide to try, I want to see the details!
G-

[ksouers]

G,
Here’s a picture of the rotor with the manufacturer info sticker. This came out of an old 5 ¼ floppy drive from late 80s or early 90s, but I suspect you’ll be able to find it in any Panasonic product from that era that needs a motor.



The spacer I need is about .060 thick, a bit more than just a few shims. I want to put ¼ inch thick magnets in it so I need to push the rotor disk away from the PCB a bit in order to fit them.

I think I’ve got enough testing in with this configuration so I’ll probably start making the spacer this weekend. I tried retapping one of the screw holes for a 2-56 thread but I guess there wasn’t enough meat left and it stripped out. I’ll redrill them all and tap for a 4-40.

I’ll first do just a single rotor and fly it for awhile then I’ll start on the double rotor mods. I’ll have to cut the screw ears off the stationary part and make a hub for it. Should be pretty straightforward. You can see the hub I made for mounting the turbine. It fits in a relief that had been machined into the part that grips the floppy disk. A couple drops of locktite keeps it in place.



I'll post pics of all the parts when I disassemble it this weekend. You'll see all the gory details as they happen.

I plan to reinforce the PCB with epoxy, maybe add some fiberglass. There is no glass in the PCB, just very thin phenolic so it wants to crack and chip just looking at it. I didn’t mess with the traces, just unsoldered the coils and wired them up in star and put some tails on the out wires The wires were then hot glued to the PCB for strain relief.

Thanks,

Kevin

[WooferHound]

That looks a lot like a Floppy drive. The wire in them is too small to make usable power.

[ksouers]

Woof, not be combative but your statement is illogical in the context of this thread. Please re-read it from the beginning.

[ksouers]

Last night I replaced the small disk magnets with the 1x1/2x1/4 inch that I have. I ended up using the aluminum spacer as I don’t have any suitable hard plastic. I tried a piece of ¼ inch foam but it got crushed easily under the force of the magnets.

I cut off about .060 thick piece from a chunk of 1 inch bar stock I found in the scrap bin. I glued that to the rotor and used the existing screw holes as a guide.

The performance difference is amazing. I didn’t really expect that much, but then again I really didn’t know what to expect. With the old magnets the most I saw was a little over 2 Voc, with the new it easily gets 4-5 Voc. The old was lucky to get 20-30 ma with 50 ma during a strong gust. The new magnets easily get 100 ma and I saw one strong gust put out 300 ma. It charges an AA battery easily.

The old magnets used to turn in just the slightest of breezes but never would put out any appreciable voltage no matter how hard the wind blew (we gusts to 40 MPH yesterday), just enough to measure. The new magnets take much more wind to start, about 5 MPH but the voltage climbs quickly from there.

I’ll fly this configuration for a week or so while I make up a new hub for the dual rotor. Step by step I’ll actually get somewhere, I hope. So far it’s been fun seeing the little improvements as I get more experience with this new found hobby. I’m slowly coming to the realization that this may never be a productive wind site. The wind is just too fluky. Although we’ve had some good wind the past couple days it’s not “normal”. Most of the time the wind here is just a small fraction of what is reported by the Weather Channel web site. The turbine often sits idle for several minutes then there is a burst of energy for several seconds or a full minute if I’m lucky before it dies down again.


G-
As promised here is the disassembled motor.




Thanks,
Kevin