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Posted: 11 January 2010 at 4:53am | IP Logged Quote MacGyver



This is what I'm building and what I want to know is: Is this an "axial-flux generator or something else?

The little dark squares are 1/4" neo-magnets press-fit into a solid aluminum plate. Each magnet in the series alternates ends. One is N/S and the next is S/N all the way around evenly spaced.

The plate is attached to the main shaft at the hub with a set screw. The way I've drawn it, it looks like a slot on the hub. That is there because I was having a PM discussion with oztules about using a spring and flyweight mechanism to move the magnet rings to varying distances from the pick up coil(s) in plan "A". The idea was to start out with the magnets far away from the pick-up coils and as the speed of the twirling turbine increased, centripital force would throw the flyweights outboard and they in turn would slide the magnets down the shaft via bell cranks so the thing would be able to start with no load.

The "B" scenario is there in case that's the true AxFx design instead of the "A" one. (I'm striking two birds with one blade here so to speak.)

When I zero in on a design, this will be driven directly from the shaft of a VAWT. (VAWT stands for vertical-axis wind turbine for newbies).

I redesigned the Lenz VAWT using both an inboard and outboard "cup" along the leading edge of each of three blades, which all circle the tower parallel to its axis. I did this after doing a wind-vector study of the Lenz to see if I could modify the already-good design to make it have more areas of "push" as each blade swings through its 360-degree, circular pathway. I think my modifications will be just the ticket. Of course, I've said stuff like that before only to wind up with egg on my face, so hide and watch!

I finished constructing the blades yesterday and will attach them to the hub and shaft sometime today. I'll be posting pictures (likely in "Windmills" and not here in "Other Stuff") though as things progress.

Right now, all I want to know is what to call what I'm building as far as the actual generator part is concerned.

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Posted: 11 January 2010 at 9:36am | IP Logged Quote niall1

hi Macgyver

i,m confused ....B (to me) looks more like a radial design but using a core in the coil with the same magnetic poles appearing at both ends seems strange...A looks more axial but the core seems to complicate things again ... A this time sees an alternating flux through the core which seems to make more sense.....

coils using alternating flux cores are very confusing to me ......one thing is i suspect it may cog heavily (feel very notchy in operation )

niall



Edited by niall1 on 11 January 2010 at 10:56am


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Posted: 11 January 2010 at 10:08am | IP Logged Quote Dinges

Quote:
This is what I'm building and what I want to know is: Is this an "axial-flux generator or something else?


Axial flux, as the magnetic fieldlines run parallel to the rotational axis as they leave the magnets.

Keep in mind that NdFeB is brittle (basically a ceramical material). For a press fit, you need your materials to be ductile. Try press fitting an oversized steel pin in a hole in porcelain, and you'll get the idea. Press fits rely on the deformability of the materials. In your case, the aluminium may deform enough. But I'm not sure the magnets won't fracture as you try to press them in.

I think I'd go for epoxy or another modern, good quality adhesive to fix the magnets into the aluminium rotor - much less that can go wrong that way.

The shear stress of epoxies on properly prepared surfaces is very impresive; did some shear tests with NdFeB magnets in the past, and in most cases it was the nickel-NdFeB bond that failed: the nickel plating stayed in its place, held by the epoxy, whilst the rest of the magnet (bare NdFeB) sheared off. IIRC, it took over 1000N for a 15mm diameter magnet to move.

Peter.

Edited by Dinges on 11 January 2010 at 10:23am
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Posted: 11 January 2010 at 11:06am | IP Logged Quote niall1

still confused .....

Peter ...i,d appreciate a lesson with regards to axial flux as against radial flux .....my heads hurting a bit now ...

Edited by niall1 on 11 January 2010 at 11:31am


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Posted: 11 January 2010 at 1:23pm | IP Logged Quote MacGyver

niall1 wrote:
i,m confused ...


Hey! Join the club.

In both cases, there is an "N" pole and an "S" pole passing by the coil-pick-up ends. In the "A" model, the coils (I only showed one in my little drawing) are mounted under the ring of magnets. This was done to facilitate a spring-loaded sliding mechanism that was to work much the same as a governor on a steam engine. This arrangement allows the magnet ring to pull back from all the ferrous coil pick-up ends when it's not spinning and approach the coils only after gaining some momentum.

I know Peter will likely not like that I am using springs against the wind, but I'm up for trying anyway. Color me consistent.

In the "B" scenario, again, the coil pick-up ends each face an "N" and an "S" as the ring of magnets whirs through the gap, but these coils are mounted around the circumference of the thing and the windmill would have to start against a fully-cogged rotor. Since this is a VAWT, start-up torque is a joke, thus the "A" scenario.

I'm thinking that the "A" model is more along the lines of an axial-flux machine, judging from all I've read about others' efforts, like on Scoraigwind, but I'm still not sure.

Someone pinch me! I'm with you niall, I need some instruction here.

Dinges wrote:
For a press fit, you need your materials to be ductile.


I realize the little magnets will explode in the arbor press, but I've done this successfully before, so I thought I'd give it another try. If all else fails, I can always machine a HDPE platform and press the little mags into that. It's pretty soft and forgiving. I chose this design, because it lends itself to keeping the magnets all lined up in a straight line and allows me to use off-the-shelf hardware for the most part.

I'd like to stay from epoxy. The smell makes me want to puke.







Edited by MacGyver on 12 January 2010 at 2:51pm


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Posted: 11 January 2010 at 9:20pm | IP Logged Quote niall1

mmm....i see now how mags are aligned , that bit is clearer

niall

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Posted: 11 January 2010 at 10:43pm | IP Logged Quote Dinges

Niall wrote:
i,d appreciate a lesson with regards to axial flux as against radial flux

In a radial flux alternator, the magnetic fieldlines leave the magnet surface radially, i.e. like the spokes on a bicycle wheel.

In an axial flux alternator, the magnetic fieldlines leave the magnet surface axially, i.e. in the direction of the axis.

Simplest way I can explain it without using figures.

Peter.
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Posted: 12 January 2010 at 8:36am | IP Logged Quote niall1

erm ...i think it might be easier and quicker to beat the explanation into me...

the rotational axis is the shaft ...so i see the parallel connection to A

so for B the flux lines leave the magnet pole on one side and want to travel over the top of the rotor (through the core ) to the other side ...does this make b axial as well ?...


regards
niall

later edit ......the penny finally fully drops ....

Edited by niall1 on 12 January 2010 at 9:17am


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Posted: 12 January 2010 at 2:40pm | IP Logged Quote MacGyver

niall1

According to what Peter has explained, I guess it's the way the magnets are aligned as to whether it's axial or radial. In my drawing, I am thinking, like you, that both "A" and "B" are axial generators; the axial-ness of it is determined by the magnet placement, which is the same in each.

If this is wrong, I'm sure Peter will chime in and correct us, but that's my take on it so far.

Now all I have to do is put all the parts together. I've finished building the blades and the hub and all the mounting parts, so I'll try to get everything together and snap a couple pics. I'm going to use the "A" configuration, as I want to be able to adjust the distance of the magnets from the pick-up coils using a home-made governor thingy I cooked up.

I want my windmill to be able to start with no load and since it's a VAWT, it's more than merely on my "wish list"; starting no-load a necessity!

I'll keep everyone in the loop.

Edited by MacGyver on 12 January 2010 at 2:54pm


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Posted: 12 January 2010 at 2:50pm | IP Logged Quote MacGyver

Dinges

Take a look at my drawing, please. What do you think about mounting another pick-up loop suspended atop the magnets as a method to make a "return pathway" for the flux lines?

From the side, it would look almost like the letter "O" elongated and with a slot at each end. I don't know if this would help generate more electricity or just cog like nobody's business.

Edit: herbelagenen -- my "new word" of the week! (re-calculating)

Edited by MacGyver on 12 January 2010 at 4:10pm


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Posted: 12 January 2010 at 5:58pm | IP Logged Quote oztules

It will make power.... but gee it seems a hard way to do it.

If you use lots of bits of paper and some colored felt tip pens and an afternoon, you may come up with a geometry that minimizes cogging. This will probably mean having to rectify each coil.... but that would be preferable to the spring and bell crank solution to startup......

Plan A will require the Al plate taking the full pull of the magnets. Single phase would rattle the thing fairly badly. If you solve the cogging (fiddle with the geometry), I would run with B as it balances the forces on the Al plate.

This thing could use up a lot of little squirrel cage motors I suspect.




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Posted: 13 January 2010 at 4:05am | IP Logged Quote MacGyver

Oz

Tell me an easier way; I'm all ears!

My concern with this thing is, as everyone already knows, the VAWT has no start-up torque. If all the permanent magnets are cozy, latched onto a pick-up coil, it'll take a mule to push the thing into motion.

I had even thought of somehow mechanically moving all the little "C" coils by swinging them into position over the magnet-holding ring after the thing was up to speed.

What I'm after is something simple, but the more I fiddle with this, the more complicated it seems to get.

So, for starters, does the way I have the magnets pressed into that aluminum ring qualify it as an axial-flux generator?

One step at a time at this stage.


. . . . . . Mac

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