The learning curve.

[ghurd]

The new magnets take much more wind to start, about 5 MPH but the voltage climbs quickly from there.

Hey Kevin,
I don't like the sound of that.

Either there is some metal in the flux path that is allowing eddy currents,
Or something magnetic close to the flux path,
Or there is a physical imbalance.

On MY stuff, I would expect an imbalance... because thats what I do. 

The iron being close to the magnetic path will feel like cogging when turned slowly.

On your stuff, it may be eddy currents circulating in PcB circuits?
I suggest snipping, pulling, removing traces, and otherwise make the PCB unable to carry current... because thats what I do.   

Yea, thats a cool little motor.
G-

[ksouers]

There is no discernible cogging, everything turns smoothly. Though it does feel a little "stiffer" when rotating by hand. I just assume its eddy currents in the backing plate. I also had to press out the bearings to tap the hub for the bigger screws so there may be a bit more friction from the bearings being reseated. But it does turn smoothly.

I balanced the turbine as best I could using a prop balancer but there is still some visible wobbling while it turns. I can't tell if the imbalance is weight or aerodynamic, though I suspect maybe a bit of both. I also suspect the blades need some tweaking to the shape. I had tried to tune them in as much as I could for the lighter magnets so I may just need a little more twist to get started at a slower air speed. All the traces are still intact on the board so that may be a factor. I do plan to eventually make some coils with heavier wire so for the moment I'm just going to leave it, I think.

Also the new magnets just barely fit in the rotor cup. The inside corners are touching all the way around. I don't know if that has an effect on the eddy currents or not. Either way I'm quite pleased with the performance. Hell, I'm just amazed that it works at all! I'm hoping that going to dual rotors will be even better.


Kevin

[ghurd]

There is no discernible cogging, everything turns smoothly. Though it does feel a little "stiffer" when rotating by hand. I just assume its eddy currents in the backing plate. I also had to press out the bearings to tap the hub for the bigger screws so there may be a bit more friction from the bearings being reseated. But it does turn smoothly.

I balanced the turbine as best I could using a prop balancer but there is still some visible wobbling while it turns. I can't tell if the imbalance is weight or aerodynamic, though I suspect maybe a bit of both. I also suspect the blades need some tweaking to the shape. I had tried to tune them in as much as I could for the lighter magnets so I may just need a little more twist to get started at a slower air speed.

All the traces are still intact on the board so that may be a factor.

Also the new magnets just barely fit in the rotor cup. The inside corners are touching all the way around. I don't know if that has an effect on the eddy currents or not.

Either way I'm quite pleased with the performance. Hell, I'm just amazed that it works at all! I'm hoping that going to dual rotors will be even better.

"Stiffer" means eddy currents somewhere... if the bearings are not out of kilter.

Get out the Dremmel tool, cut those traces, all of them, twice, with a vengance, and remove all the parts that are not required.
A cap is like a dead short some of the time.  Resistors are sort of shorts.  Etc.

"The inside corners are touching all the way around. I don't know if that has an effect on the eddy currents or not"
That would not be a major eddy current issue.
That would be the flux path being shorted, meaning the flux is bypassing the coils by going through the cup's edge, which is a major issue.
Make the cup into a plate.

Dual rotors will about double the output, depending on the rest of the situation.
I think you could get it trippled if the issues are fixed.

No need to get it spinning before 4MPH, except to prove it does not have issues with balance, eddy currents, etc.
G-

[klsmurf]

Ksouers,

Sorry if I'm intruding on your thread. I like your small project. Big is not always better. I've got a few small motors myself just waiting for something to be attached to. To that end....



@ Mr G-

I am assuming that this is one of the "good ones" you spoke of in the link you posted earlier? It's from a VCR that I had stripped earlier.
How many leds could be lit? Just the six that was shown in the link.   Thanks

[ghurd]

Yes, thats the good kind.

The ones I tried could light up a lot of LEDs (in parallel).
Considering you can tell an LED is light up with 0.5ma, and the ones in a ghurd controller only use about 3ma, it means there is much power required to light up quite a few LEDs.
G-

[ksouers]

Minor update.

Did a couple things. Today we had some rather gusty winds. In the past I'd take the tower down when it got too windy but today I arranged things for a sort furling to occur.
The turbine is mounted on a piece of plywood with a large hole in it. It's actually the piece from the blade hub was cut from. A single long screw holds everything on the bar of the wind mill.
I just turned the turbine mount to the side a bit, this causes the bar to offset a bit on the stronger gusts. It still has a straight tail so it doesn't fold up. But it really will turn during a strong gust and doesn't put as much stress on the tower.
It does hunt around a bit during the strong gusts as it "furls" and the tail tries to push it back, but it's been pretty effective in controlling the bending and loading on the tower and on the blades.



The other thing I've done is put a "voltage doubler" before the rectifiers. It's just capacitors in series as per the article pointed to by oztules in this post.
http://www.anotherpower.com/board/index.php/topic,271.msg2260.html#msg2260

It works OK. It does up the voltage a bit, but as expected the amps are low. When you already start out with low amperage it really doesn't help the situation much, but I have been able to charge a 4-pack of nimh batteries with it. I've also been able to do that without the caps but it did take a little longer, so in that regard I could call it successful. I suspect it'll perform better once I make some coils more appropriate for the task.

Now, I need to drain some more batteries just so I can charge them up again.

Thanks,

Kevin

[ghurd]

What is the angle on the blades?
Looks kind of steep in the pics.  Actually, it looks WAY too steep between the 2 pics.
It also looks adjustable.

Might try the blades a little flatter to the wind.
The RPM will increase a lot, and power output shoud increase more than that.

G-

[ksouers]

Hi G,
The angle at the root is about 15 degrees and flattens out to about 2 degrees at the tip. It's not very precise as the foam is quite flexible and they have suffered several repairs. They were flatter at the root but I had difficulty getting it to start in mild winds when I put the larger magnets in it so a little extra twist was added. When the wind does pick up it will definitely spin it's little head off. I've yet to get a reliable measure of RPM, I've tried the wireless bicycle speedometer but I think the magnet rotor interferes with the pickup. I need to play with it more.

I should make a new set of blades, these are pretty battered and have had many repairs on them from tower strikes or being completely blown off in storms. The original intent was to make them adjustable and that worked up to a point. But that adjustability also made them prone to falling apart at high speed.


Kevin

[ghurd]

I would be worried about the flex making the tips go negative AoA.

Might be time to make them out of wood?
G-

[ksouers]

I love having days off so I can play

Over the past couple days I've been winding new coils from #26 wire. Yeah, I know, it's still small. Anyway, 6 coils, 100 turns each. And a sloppy job of it, too. Couldn't get the tension right. Ended up with 1 coil too tight and 2 that were too loose. The other 3 were so-so, not good. I think it was too many turns for too small coils. Mounted them to some perfboard in the same fashion as the original coils. They are also thicker than the original so the air gap is also greater.

Performance sucks, for the most part. Using the caps doubler I only saw a max of about 2.5 volts and an occasional 80-90 mA. Most of the time around 20 ma. Barefoot was an easy 2.5 volts and 140 mA, though I did see 5 volts and 500 mA on one good gust. So, the doubler was a bust in this experiment. Bigger caps maybe?

I did flatten out the blades a little, got the twist and angle a little more even. Can't say it made an improvement, but I can't say it didn't either. The biggest improvement by far came from shortening up the blade by 2 inches. Starting seems easier oddly enough, certainly RPMs seem higher. There is less hunting, it seems to have a more stable point into the wind.

I also messed around with trying to get a good reading on RPM but no dice. The best I could get was an initial reading for about 3 seconds and then nothing but 0. I have another unit to try, we'll see if that's any better.

Ghurd, I was worried about the flex having a negative impact on AoA also, but that doesn't seem to have happened. At least not that I can point to definitively. The spar is just slightly forward of 50% chord, so perhaps I've just been lucky and I'm not getting any additional twist. An ultra high speed camera would be nice to prove it one way or the other

Yes, wood blades are definitely in the future. Not sure that I'm ready for them just now, but it will happen fairly soon. I think I want to try one more set of foam (yes, I'm stubborn).


Kevin

[oztules]

You have a very low pole count, so you will need a heap of caps.... but they will do it when you have enough reactance for your low frequencies and pole count.... maybe Gordon will comment.

...............oztules

[ksouers]

Thanks, oztules. I'm not too concerned about the output of the caps, or the lack of output. This is, after all, just play time. A chance for the innocence of ignorance to dance with curiosity and discovery.

Over the weekend I got parts made up for the dual rotor conversion of the little motor, using the backing plate for the second rotor. I'll take some pictures later and describe the conversion. It's really quite simple, but it's very sloppy.

Anyway, it's eight poles, same as the single rotor but now a total of 16 magnets. I'm still using the original coils. I've also run with the cap doubler and barefooted. The double is definitely putting out way more volts now. Barefooted I've hit a max of about 8 Voc in very strong winds but most of time it floats around 3-5 Voc. During the strong gust I also saw just over 400 mA.

With the doubler I saw a max of 13 Voc with volts climbing quickly to around 8-9 volts even in mild breezes. I've also seen 200 mA in strong gusts, but most of the time around 40-50 mA.

I also went digging around the scrap bins for pieces to make up a more permanent set up. Got a nice big square chunk of aluminum for a bearing block, some 1/4 x 1/2 ball bearings and a piece of 1/4 brass rod and 1/4 O1 drill rod (silver steel). Not sure which I'm going to use for the axle rod. The brass fits the bearing perfectly. The O1 is about .001 over size so it'll need a little work to make it fit. I'd prefer the drill rod but the easier brass appeals too.


Thanks,

Kevin