using hallbach array

H

Hummina Shadeeba

10 MW
Joined
Apr 25, 2014
Messages
3,112
Location
Sausalito
I'm making a hub motor for a skateboard.
the stator I took from a Tacon 160 with the windings still attached at I plan to convert it to a wye wind to lower the kv but the magnets that were with it are not coming out no matter how long it sits in acetone so I'm getting others. Looking at the magnets that came with it as a guide they just cover the stator lengthwise and are 3mm thick which in the little info I've found seems ideal. Only 70 percent of the ID circumference is covered though and I'm wondering about that as I've seen completely covered rotors and heard that 80 percent is optimum. Making a hub motor for a skateboard I'm thinking as much flux as possible is ideal and part of me wants to jam as much meat in the can as I can but I read that's fraught with obstacles of harmonics, maybe saturating the stator, or inversely effecting the back-emf the controller reads. I don't know how thick the stators lams are. I'm planning on getting curved magnets at maybe N48 (st or whatever the higher heat version is..think they're good to 212f) and going for a .5mm airgap
Otherwise I'm feeling it'd be safest to just copy the magnets that came with it..but I'd prefer to jam it up as I said, thinking that will reduce the kv and give flux and torque which I'll need
 
If glue does not come off, try to compress the rotor's shell to oval shape a couple of times. Try to get a perfect oval shape (best to use a vice, wider than length of the shell) to avoid cracks in magnets. Glue should come off easier.
 
the rotor was only 67percent filled with magnets anyway and I'm thinking why not jam it with curved, high-heat N48s in a hallbach array?! Because no one is telling me not to and that sounds pretty badass.
the magnets are also glued in with what looks like j and b weld
 
I'm wondering if it's a safer bet to go with 80percent fill with nice curved magnets or go the whole hog with 100percent fill and a Hallbach array.

I know this as change in magnets will change the kv as well as other things and thats a boon for me but I'm worried about possibly oversaturating the stator with flux...or having poorly directed flux that causes noise or inefficiency...and then will the controller have to be adjusted for the higher back emf???
I dont know about any of these possible risks but the benefit of having a lot more torque with a low kv is a big plus being a small hub motor
 
Magnet width along with the stator tooth head geometry is what creates the shape of the BEMF on the motor.

If you increase magnet width, BEMF will change, if it happened to be sinus before, it will no longer be. This could cause everything from an entirely broken motor that doesn't work, or perhaps even improve performance if it were hopelessly off as originally designed.

Going to a halbach array off the same strength magnets alone should roughly cut your kV by half. (just as a rule of thumb to be aware of)
 
You're the only person who's said bigger magnets could be so detrimental as to make a motor not work. Making me think I should stick closer to the original magnet width then.
The magnets that came with the rotor, and I can't get out, are 33 x 9 x 3 and I'd like to do a Hallbach array with 34 x 10 x 3 magnets. Was going to do curved but doing a hallbach array seems by far the best and cheapest way to increase flux in the air gap. Wondering why it seems to be never done in any motors I've ever seen.

I always see pictures of hallbach arrays with blocks or in a ring and as I'd want to do it for a motor the shape I'd use would be different. Please confirm my method here:
I'd use a total of 70 magnets.
5 magnets to each array each roughly 7 x 9 x 3 making an array 35 x 9 x 3
after gluing these 5 together into a 35mm bar I'd place it in the rotor with 13 others.

As long as I can get the magnets made with the right pole orientation, which I doubt will be a problem, seems easy enough.
Seems every motor could benefit from this or does the back iron do a pretty good job of accomplishing the same result?
 
how much flux can you get with just low carbon steel flux ring? these seem to show that without a hallbach flux is getting lost. wonder where it's going or if a thicker or lower carbon ring would help
 

Attachments

  • hallbach 2.jpg
    hallbach 2.jpg
    80.8 KB · Views: 561
  • hallbach christian.jpg
    hallbach christian.jpg
    78.7 KB · Views: 561
I want to use an already wound stator from the tacon 160. 12 x 14 pole outrunner. 60mm.

I don't know how to find the wind scheme but how would it matter? the only problems I though would be the shape of the magnet pole compared to the stator teeth. the difference between the 67 percent fill and effectively 50 percent with the hallbach ring seems a minor difference compared to what I've seen guy on instructables doing making hub motors doing 100 percent fill. I'd have thought going with a smaller magnet would be more ideal as the flux would be coming from a more specific location as apposed to a wide magnet.
And maybe id have to worry about oversaturating the stator with flux
 
Hummina Shadeeba said:
I want to use an already wound stator from the tacon 160. 12 x 14 pole outrunner. 60mm.

I don't know how to find the wind scheme but how would it matter? the only problems I though would be the shape of the magnet pole compared to the stator teeth. the difference between the 67 percent fill and effectively 50 percent with the hallbach ring seems a minor difference compared to what I've seen guy on instructables doing making hub motors doing 100 percent fill. I'd have thought going with a smaller magnet would be more ideal as the flux would be coming from a more specific location as apposed to a wide magnet.
And maybe id have to worry about oversaturating the stator with flux
Click to expand...
Do you actually know how you motor is wound and where the magnets suppose to be and which polarity in respect to stator teeth?
 
I don't know how it's wound and don't know how to find out. The magnet polarity switches n to s continuously.

At this point I'm hoping I could replace the 67 percent fill will roughly the same. It has (14) 33x9x3 magnets and I'm wondering if I can make a Hallbach or stelter array. Don't know what I'd be making but filling the same space with bars (11) 9x3x3 bars. This isn't a multiple of 5 so maybe 12 would at least be better ?
What u think.
Maybe simply add two magnets on the side of a 33x9x3 mag but I preffer the plan above
 
Hummina Shadeeba said:
I don't know how it's wound and don't know how to find out. The magnet polarity switches n to s continuously.

At this point I'm hoping I could replace the 67 percent fill will roughly the same. It has (14) 33x9x3 magnets and I'm wondering if I can make a Hallbach or stelter array. Don't know what I'd be making but filling the same space with bars (11) 9x3x3 bars. This isn't a multiple of 5 so maybe 12 would at least be better ?
What u think.
Maybe simply add two magnets on the side of a 33x9x3 mag but I preffer the plan above
Click to expand...
For hallbach you should keep same field shape but fitt same amount of magnets between those you already have with different pole orientation NS from side to side instead of existing NS face to back. Hope you understand what I mean. :lol:
 
Hummm. I understand how the Hallbach array is typically made with 5 magnets and their orientation but it's almost always shown with blocks/cubes, I'm wondering if I could use extended cubes with the same or similar results. So instead of doing 33 magnets to fill a 33 x 9 x 3 space maybe I could use 9 x 3 x 3 extruded cubes and only need 11 magnets and be easier to make. Hard to work with 3x3 blocks.
It seems there's a lot of lost flux in every motor I come across according to the paperclip test.
 
Hummina Shadeeba said:
Hummm. I understand how the Hallbach array is typically made with 5 magnets and their orientation but it's almost always shown with blocks/cubes, I'm wondering if I could use extended cubes with the same or similar results. So instead of doing 33 magnets to fill a 33 x 9 x 3 space maybe I could use 9 x 3 x 3 extruded cubes and only need 11 magnets and be easier to make. Hard to work with 3x3 blocks.
It seems there's a lot of lost flux in every motor I come across according to the paperclip test.
Click to expand...
Not necessary, you just accomplishe job of back iron with magnets and I believe it's doable with just 1 magnet in between or 3 magnets by your formula.
http://www.google.com.do/url?sa=i&source=imgres&cd=&cad=rja&uact=8&ved=0CAwQjRwwAA&url=https%3A%2F%2Fwww.kjmagnetics.com%2Fblog.asp%3Fp%3Dhalbach-arrays&ei=r9ROVaTBFYrmsATs_YHABQ&psig=AFQjCNECEIuH_03kVYJhZINVEPeX_BNzKA&ust=1431316015434923
 
I wish I understood you better.
I've seen that page and it's interesting because they say, and show with their graph, a magnet with simply a good back iron is stronger than Hallbach. The papers I posted show a back iron only able to direct I think it was 78 percent of the flux but a hallbach array was doing 98 or 99 percent! that's a huge difference: magnet store saying they're not powerful as back iron and these papers saying hallbach is stronger than back iron. I wonder what's the truth and I'm going hunting for extruded blocks to try to make some arrays today. my mom is nowhere around so I do as I want.
 
Hummina Shadeeba said:
I wish I understood you better.
I've seen that page and it's interesting because they say, and show with their graph, a magnet with simply a good back iron is stronger than Hallbach. The papers I posted show a back iron only able to direct I think it was 78 percent of the flux but a hallbach array was doing 98 or 99 percent! that's a huge difference: magnet store saying they're not powerful as back iron and these papers saying hallbach is stronger than back iron. I wonder what's the truth and I'm going hunting for extruded blocks to try to make some arrays today. my mom is nowhere around so I do as I want.
Click to expand...
Your case is k=4 on last picture of linked page, your rotor has in and outside facing magnets, missing those in between. How big are the gaps between existing magnets?
 
I put together eleven, making roughly the 33x9x3. I want to mimic the magnet dimensions/fill that came with the stator. But these are not cubes. They are extruded cubes.

this 11 piece configuration I did is an extended version of the first or "standard" pic...so two more magnets beyond the picture on each end both facing outward. the shape of the wave I don't know but maybe it's not ideal and I wonder. Other than the unknown shape of the wave I see it as a success as the strength is greatly increased.

http://cegt201.bradley.edu/projects/proj2004/maglevt1/halbach.html
 
I'm still a bit worried doing the Hallbach even though they cover the same area as the original magnets. You think the back-emf difference will be too much for the esc. I'm also worried the flux shape, while said to be more sine with the Hallbach, maybe it's not since I'm doing 11 magnets.
 
Hummina Shadeeba said:
I'm still a bit worried doing the Hallbach even though they cover the same area as the original magnets. You think the back-emf difference will be too much for the esc. I'm also worried the flux shape, while said to be more sine with the Hallbach, maybe it's not since I'm doing 11 magnets.
Click to expand...
I do not know if ESC will have problems with emf but, for your winding sheme to work, you need to keep your stators magnetic shape in respect to magnetic pole pairs. How did you get 11 magnets? In regular case they should be divisible by 2, in your case even by 4,since you use 2 magnets per pole or 4 per pair.
 
In the picture:
http://cegt201.bradley.edu/projects/proj2004/maglevt1/halbach.html

I did the nine magnet standard version, then to suit my dimensions I added two more magnets. It is strong as I say...maybe 9/1 ratio but I have to make a test to see. Maybe hang a bunch of nails in a string maybe. The shape of the flux and how that will effect the back-emf I don't know?

I think I want a "perfect wave" of flux. I think it will produce a better back-emf wave that will be more efficient and also be read by the esc better. but that is a guess and thought someone here would know.
 
I'm lost! Do you want to levitate stuff and play with linear pattern or spin a motor?
If second one, you must ASAP forget all this linear patterns and concentrate on understanding how your motor works, what motor pole pairs are, how motor toots are wound, what winding schemes work for your stator toot count, and finally, which stator tooth count, winding scheme and rotor pole pair count/configurations work together.
I may repeat my self, but if you do not want to go so deep then, just take your rotor, count your magnets and you have the Number of Poles you need to keep in your hallbach array. Since you need at least2 magnets per pole (the way you are doing it) your hallbach will have double amount of magnets then in original rotor, Pole count stays same.
 
I took apart a Tacon 160 motor and am using it's stator with windings and mimicing the magnet location and fill. It is a 12 pole/ teeth stator wound to 245kv. The rotor has 14 magnets and I will keep to the same magnet fill of 67 percent. Im leaving everything the motor came with the same except replacing the magnet strength.

Maybe I am wrong but there are only two variables in my situation that I wonder about:
1.
the strength of the new magnets is much more and I wonder how that will affect the esc
2.
the new flux shape will change and I wonder how that will effect the motor's performance.


(I'm assuming the extra strength will only help my motor unless the stator cant handle the extra flux and becomes saturated easily)
 
You must log in or register to reply here.

Similar threads

Kodin
Tank Bike - (Previously: Yet Another Genesis)
2
Replies
28
Views
12,152
Kodin
Kodin
Reid Welch
"Extreme MY1018" archival, closed out
Replies
11
Views
18,028
GIGATT
G
Back
Top