Author Topic: And so it begins  (Read 11505 times)

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Offline ksouers

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Re: And so it begins
« Reply #15 on: February 05, 2012, 01:49:28 pm »
That's damned impressive, Chris! I sure do like the way you farm guys build stuff.


jlt: Thanks for stopping by. Interesting suggestion, I must say. I may try that when I start experimenting.


Just got off the phone with a friend that has access to a water jet where he works. They keep 1/4 inch plate stock on hand, so arrangements will be made to have the rotor plates cut within the next couple weeks. All dependent on the jet operators schedule.

My plan is to face cut a wide groove in the plates maybe 1/8 inch deep to hold the magnets, result will be something similar to what Chris did with the cleats. Then all potted in resin.


Kevin
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Offline ksouers

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Re: And so it begins
« Reply #16 on: February 06, 2012, 05:15:16 am »
I've read some comments that mention a "stall" condition.
Could someone describe this, please?

When I see that term I think of an aerodynamic condition where an airfoil loses lift, usually at low speed and high angle of attack, but it can occur at any point in flight under the right conditions. Essentially, it's cavitation on a large scale.
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Offline ghurd

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Re: And so it begins
« Reply #17 on: February 06, 2012, 09:39:37 am »
I've read some comments that mention a "stall" condition.
Could someone describe this, please?

When I see that term I think of an aerodynamic condition where an airfoil loses lift, usually at low speed and high angle of attack, but it can occur at any point in flight under the right conditions. Essentially, it's cavitation on a large scale.

That's right.

In a wind turbine, the blade RPM slows when the PMA is loaded more.
If the PMA is loaded too much, the blades slow down too much.
When the blades slow too much, the angle of attack becomes huge, and the blades can't make much lift (or power).

In a wind turbine, typically when it is 'stalled', the power output kind of hits a plateau, even when the wind speed increases.
Say it makes 2A at 8MPH, 2.5A at 9MPH, and 2.5A at 15MPH?  That's an indication it is stalled pretty hard.

Make sense?

G-

Offline jlt

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Re: And so it begins
« Reply #18 on: February 06, 2012, 12:13:16 pm »
  An easy way to keep mags from sliding off is to make a band around the outside of the rotors.

   Just make a band out of mild steel or stainless.Make the band 1/4 inch smaller than the rotors.
   Heat the band to a cherry red and it will expand enough to slip over the rotor. when it cools it will
fit very tight.

        If you use  mild steel only leave 1/8 sticking above the rotor. If you leave the band to tall there will be some cancellation.

Offline ksouers

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Re: And so it begins
« Reply #19 on: February 06, 2012, 06:19:26 pm »
Thanks ghurd. I've been having trouble trying to visualize the aerodynamics of the blade, now I have more to think about. I can't quite get my head wrapped around the relative wind hitting the airfoil on the bottom (very high AoA) then the transition to rotational motion with a frontal relative wind. Sometimes I think I have a grasp of it then it slips away. It's the transition that gets me. It'll click eventually. At least now I know what people are talking about.

jlt: I saw that on the "other" site. Seems like a pretty good trick. Any drawbacks to cutting the groove? I don't have any welding equipment though I can silver solder using propane, and I have a broken band saw blade laying around that I was going to repair, though that's a very high carbon content. I think I've read of problems with high carbon steel laminates.
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Offline klsmurf

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Re: And so it begins
« Reply #20 on: February 07, 2012, 08:05:36 am »
Hey Kevin,  Kevin here.

I'm watching you start up with interest. You are asking some good questions, especially on this new forum.

You stated earlier in the thread that you weren't sure about the addiction thing. As they say, Denial is the first sign.

I am curious about this:
Quote
My plan is to face cut a wide groove in the plates maybe 1/8 inch deep to hold the magnets, result will be something similar to what Chris did with the cleats. Then all potted in resin.
Are you planning to recess the magnets in the rotor? IIRC there was a discussion over at the other place about this. (haven't looked it up 'cause I'm not sure about linking to over there) Being 50+ with occasional CRS, maybe one of the experts will chime in. I am under the impression that recessing the magnets will disrupt the flux pattern. To my uneducated logic, recessing a 1/4" magnet 1/8" into the rotor will cause problems. Disruption of flux and leakage out the back.

Hopefully one of the experts will correct me. Just didn't want you to find this out too late. Keep it up.
"A man's got to know his limitations" ---- Harry Callahan

Offline ksouers

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Re: And so it begins
« Reply #21 on: February 07, 2012, 09:09:41 am »
Hi Kevin. Thanks for stopping by.

I'm watching you start up with interest. You are asking some good questions, especially on this new forum.

Thanks. I'm trying. I have a lot of curiosity and little knowledge on the subject.

Quote
You stated earlier in the thread that you weren't sure about the addiction thing. As they say, Denial is the first sign.

I will admit addictions to curiosity and experimentation :)

Quote
Are you planning to recess the magnets in the rotor? IIRC there was a discussion over at the other place about this. (haven't looked it up 'cause I'm not sure about linking to over there) Being 50+ with occasional CRS, maybe one of the experts will chime in. I am under the impression that recessing the magnets will disrupt the flux pattern. To my uneducated logic, recessing a 1/4" magnet 1/8" into the rotor will cause problems. Disruption of flux and leakage out the back.

Welcome to the +50 crowd. I blame a lot of stuff on that :)

The plan was any groove, just deep enough to keep the magnets from slinging off the rotor. Maybe not 1/8 inch, but a few thousandths, if it's not detrimental. I've also thought maybe a ring of non-ferrous metal (brass?) or a ring of plexiglass or fiberglass would work. Though I suspect getting the plastics to bond, and stay bonded, to the steel rotor may be more trouble than it's worth. The metal band mentioned by jlt is also intriguing. Simple and elegant. I thought a pocket would mess up the flux but maybe a groove would not. I just don't know. I, too, am hoping someone will have an opinion about it.

Thanks,
Kevin
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Offline Dave B.

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Re: And so it begins
« Reply #22 on: February 07, 2012, 01:06:03 pm »
Kevin,

  Use a quality epoxy adhesive with a very thin bond at the magnet. Clean both surfaces very clean with maybe acetone or similar. Use the same epoxy to run fillets around the magnets after the initial bonding has set up. The key is proper preparation of the surfaces and quality epoxy. Completely potting the magnets looks pretty but I have never found it necessary. Do not use Bondo, it is not an adhesive, it will crack, hold water, rust and destroy your magnets. Yes, flying magnets could be an issue using Bondo, it's how this all got started about needing to fully pot the magnets. It's a problem that does not exist when properly done.  Dave B

Offline ChrisOlson

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Re: And so it begins
« Reply #23 on: February 07, 2012, 03:19:41 pm »
I am under the impression that recessing the magnets will disrupt the flux pattern. To my uneducated logic, recessing a 1/4" magnet 1/8" into the rotor will cause problems. Disruption of flux and leakage out the back.

Some folks claim that, but it's not true.  I made a video once of testing that with the "claws" on the outside of my ferrite magnet rotors.  I thought I had uploaded the video to YouTube but I can't find it right now.  At any rate, putting 1/8" thick x 3/4" wide "claws" on the outside of even those very weak magnets did not make one bit of difference in the magnetic performance.  Not even .01 volts on a spin test with a generator that doesn't have them vs one that does.  All it does is redirect flux that leaks out the perimeter of the rotor anyway.

I know I had sent that video to Hugh (Piggot) at one point, and I thought I had uploaded it to YouTube.  If I find it I'll post it.
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Offline ksouers

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Re: And so it begins
« Reply #24 on: February 07, 2012, 03:33:27 pm »
Dave B: Thanks. I never even considered Bondo. I usually run from the stuff. Hideous! I had planned to use West Systems as it's readily available. I've also had good experience with Devcon under adverse conditions.
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Offline klsmurf

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Re: And so it begins
« Reply #25 on: February 07, 2012, 07:38:50 pm »
Hey Chris

Quote
Some folks claim that, but it's not true.
I don't know that I'm ready to agree with this blanket statement. Your big honkin ferrites are sitting on a full thickness rotor with "claws" on one outer edge only. I'm talking about thin neos recessed into the rotor. I don't know for sure but, to me it seems to be apples and oranges.  It's probably a moot point as it sounds as if he (ksouers) will be using another method. I would be interested to see the modeling of neos sitting in pockets on a rotor.

Kevin

BTW I enjoy seeing and reading about your projects. Gives us wanna-bes something to shoot for.
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Offline ChrisOlson

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Re: And so it begins
« Reply #26 on: February 07, 2012, 08:41:26 pm »
I don't know that I'm ready to agree with this blanket statement. Your big honkin ferrites are sitting on a full thickness rotor with "claws" on one outer edge only. I'm talking about thin neos recessed into the rotor. I don't know for sure but, to me it seems to be apples and oranges.

Actually, the best modeling is to actually do it and spin the two varieties on a real world stator and see what you get.  I recessed 1/4" thick wedges that I bought from Ed Lenz that didn't have any holes for pins years ago and never had a single problem with it.  Got the same voltage from those generators as the books and spreadsheet calculators said I should get.  I used to leave a .150" rim on the edge of the rotor when I machined them.
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Offline ksouers

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Re: And so it begins
« Reply #27 on: February 07, 2012, 09:51:58 pm »
I would be interested to see the modeling of neos sitting in pockets on a rotor.

Kevin
I had already discounted using a pocket very early in the decision. Mostly because I didn't really want to stand in front of the mill for days on end carving out 40 little pockets in hot rolled steel plate!

My intention was to machine an => inch wide groove in the rotor face, maybe .030 to .125 deep leaving a rim around the outer edge ~.020 - .050 inch. Still holding out deciding what to do seeing how this argument plays out. For those keeping score I'm siding with Chris so far. Hard to argue when someone can prove by example it doesn't make a difference.

Kevin
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Offline ChrisOlson

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Re: And so it begins
« Reply #28 on: February 07, 2012, 10:03:05 pm »
My intention was to machine an => inch wide groove in the rotor face, maybe .030 to .125 deep leaving a rim around the outer edge ~.020 - .050 inch. Still holding out deciding what to do seeing how this argument plays out. For those keeping score I'm siding with Chris so far. Hard to argue when someone can prove by example it doesn't make a difference.

You could set up the mill and mill out pockets.  But it's a lot easier and quicker on the lathe.  I've always machined my rotors by facing them so they run perfectly true.  I always took .150" off to get all the humps out and get the face of the rotor nice and flat, and left a rim about .050" around the outside for the magnets to butt up against.

On later turbines I went to using bar mags with holes for pins so I didn't do that.

On the ferrite turbines, each one of those magnets weighs over 3/4 lb.  I didn't trust the little lip like I've done in the past.  The centrifugal forces on those are astronomical when you got a generator running at 1,200 rpm like it does in my latest turbine.  So there I welded 1/8" x 3/4" pieces of flat stock to the outside of the rotor to hold the mags against the force.  Somebody told me when I posted pictures of the first one that it "steals flux".  And that's why I made that video on it.  I still haven't found that confounded video.  I think it's in my computer with a name like 100-3823.wmv or something and I'm still trying to locate it.

Hah! I found that frickin' video.  I'm uploading to YouTube.

OK, here's the video.  Later, after I made this video I bought a gauss meter.  What I found is that these axial rotors saturate around the edge of the disc and you get flux that leaks because even a 1/2" thick disc will saturate right near the edge.  Leaving a "lip" or weld on "claws" only stops the flux that leaks normally anyway, and it doesn't make one iota of difference in airgap flux between the two rotors.


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Offline Watt

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Re: And so it begins
« Reply #29 on: February 07, 2012, 10:41:47 pm »
Chris, thank you for sharing that video.   8)

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