Author Topic: Is my skewing right?  (Read 3064 times)

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Bobbyb

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Is my skewing right?
« on: August 25, 2006, 11:40:55 AM »
Hello,


I'm doing a motor conversion and am going to mill my rotor very soon.


so i made teas cad drawings.


the magnets are 9mm x 9mm x 50mm and there are 8 of them on the rotor



In this topic i read that one must divide 360 degrees by the number of slots (24 in my case).

http://www.fieldlines.com/story/2006/6/23/185558/084

so as u can see in the drawing i skewed my magnets at a 15 degree angle (looking from the end of the rotor)


the 2 lines i got from that angle are used to place the magnet's.

The center of the magnet at the ends is placed on these line's.

c the picture :)


Have i dun this right?


Another question is: what is the idea behind skewing?


I know its to prevent cogging but is it like, when the flux "pulls" 3 or so stator slot's then its..????

Hope u get what i mean.


And another thing I'm pondering about.

I can put my magnets in/on the rotor two way's


One way i get the most flux on top of the magnet


The other is when i rotate the magnets 90 degrees i get the most flux on top of the Pease of rotors between the magnets.


There might be a difference because the magnets will not be as close to the stator as the rotor pleases will.


I will test the two options anyway but what do u think??

« Last Edit: August 25, 2006, 11:40:55 AM by (unknown) »

drdongle

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Re: Is my skewing right?
« Reply #1 on: August 25, 2006, 06:01:19 AM »
Your illustration suggests that you plan to cut slots to hold the magnets. This is not a good ideas as the iron surrounding the magnets will divert most of the flux away from the face that is towards the stator greatly reducing the available out put from the PMA. Search the board projects by Zubbly to see how it can be done.
« Last Edit: August 25, 2006, 06:01:19 AM by drdongle »

Countryboy

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Re: Is my skewing right?
« Reply #2 on: August 25, 2006, 07:08:36 AM »
Your skew angles are correct.  However, it's unwise to use this method of skewing with these magnets.  Your CAD program doesn't recognize that the magnets are a rectangle with parallel sides.  Your CAD program displays them as being twisted on the poles, so they fit the curved rotor.  If you use these magnets skewed this way, the end corners of the magnet will have a smaller airgap to the coils than other parts of the magnet have.  If you want to use these magnets, either skew the stator laminations, or use the JacquesM method of skewing.


The purpose of skewing is so that all stator teeth always see the exact same amount of magnet material, regardless of rotation - and the magnets always see the same amount of tooth material.  If a stator tooth sees more magnet material at certain points in the rotation, it will require more force to turn the magnet past that point.  This spot requiring more force is known as a cog.

« Last Edit: August 25, 2006, 07:08:36 AM by Countryboy »

shmuu102

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Re: Is my skewing right?
« Reply #3 on: August 25, 2006, 03:44:04 PM »
can the skew angle be taken from the original induction rotor assembly?


i have one that i can clearly see the skew angle on he lams on the rotor...

would it stay the same?

« Last Edit: August 25, 2006, 03:44:04 PM by shmuu102 »

dinges

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Re: Is my skewing right?
« Reply #4 on: August 25, 2006, 04:00:25 PM »
Your skew angle is correct, your 3D CAD drawing not.


With magnets as you have, you might want to try another de-cog system:


http://www.fieldlines.com/story/2006/8/12/213549/997


should be pretty easy to make if you have milling capability. Also, your airgap can be smaller.

« Last Edit: August 25, 2006, 04:00:25 PM by dinges »
“Research is what I'm doing when I don't know what I'm doing.” (W. von Braun)

Bobbyb

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Re: Is my skewing right?
« Reply #5 on: August 26, 2006, 09:46:20 AM »
Thx four all your advise


I'm still going to do it my way and look what kind of power i will get.


this is sort of a study conversion so if this fails I'm skewing the stator.


the goal is 40Watt


thanks again an I'll post the results.

« Last Edit: August 26, 2006, 09:46:20 AM by Bobbyb »