Dual rotor axial flux motor design

Kingfish said:
If the coil is tapered as you recently suggested, the end-turns do not contribute to the motor other than affecting losses, so that’s a good place to make the links to other coils.
Linking on the endturn reduces the coil cross-section across the bridge (I'd rather avoid taking the link around the corner..... :) ). It's only for 1mm of length, though.

Unfortunately, linking on the outside creates an extra endturn of the longer variety.... More inactive copper with 5t than with 4t or 6t...... :(

If I went to 2 x 2t and made the link on the inside endturn (under the terminations), the cross section of the bridge would only be a third of that of the rest of the coil (for circa 1mm in length)...... How detrimental would that be? If it's just the extra resistance, it hardly makes any difference but could there be any other problem?
 
Miles,
I noticed that (as you mentioned) the crossover/bridge strip to the two coil halves is not as wide as the coil half strips themselves. I encountered this problem as well and for me is was even more pronounced since my lam core is not as wide as yours is, tapered or not. My copper strips are much wider than yours, so, instead of folding the copper strip, I am using solid copper 12 ga as the crossover/bridge and have a fixture that allows me to solder the two strips to the 12 ga wire. This works well for me. My lam is not as complicated as yours is and I offset the lams (all same thickness) to form a rounded recess in the base to place the 12ga wire crossover/bridge. This also results in the top and bottom of the lam core to be rounded (somewhat) so no sharp corners in the strip winding path. It has been interesting watching your progress.
kenkad
 
Hi Ken,

Thanks for the suggestion. I'm still dreaming of a solder free motor but soldering on a separate bridging strip would certainly do the trick. I guess the ideal thing, in my case, would be to use a flattened D section for the bridge strip.
 
This is what the bridge looks like, at the moment (for 4t version). The copper would be cut from sheet in nested strips.
 

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Miles,
Just to be sure, for others who may be following this thread, I have attached a JPG of what I described earlier using a 12 gauge solid copper wire as the crossover/bridge. I colored the different lam layers for beter visibility. Hope this helps.
kenkad
 
Ken,

Nicely illustrated.

I see you have your laminations running radially. I didn't think that was optimal but, there again, the Lynch motor has them running that way, so....... :)
 
Miles,
I know what you mean. Its a PITA we all cannot be experts in everything, although I do try hard. I do not know all the answers. I do know that it is very hard to make the design simplify fabrication. I just could not justify all the fancy copper strip cutting, etc. Same with the core lam. I may have a taker to do my motor 3D FEM analysis. A PhD student at LSU wants a crack at it. He will try sometime in April after his thesis defense. For me, it was worth waiting for such a thing to happen. I have encouraged him to write a paper on this because I have not seen this type of design (multi 3-phase) in the literature. I have high hopes this all comes to pass and then we can get on with a couple of prototypes to check the theory.
kenkad
 
Just wondering if it would be feasible to laser cut the laminate stack....? 14mm cut depth in steel isn't too extreme....
 

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Hey Miles, just wanted to poke my head in so you didn't think I disappeared. Had a busy couple of weeks, so I'm just getting caught up. I have the data from all the runs I set up for while I was gone partially processed, and there don't really seem to be any surprises. More iron, more magnet -> more torque. I'd need to look more closely to see if there's an optimal point. I guess you're trading iron for copper, so it's peak torque against losses. Maybe we need to estimate how much heat dissipation you'll get, then we could estimate the continuous torque for a given configuration.

I think the wedge-shaped cores you've been modeling are a reasonable way to go. Certainly the simulation results so far indicate that more iron is better, even more so if you're replacing air with iron and not reducing the copper volume. It won't make the simulation harder, but it will be less accurate because you're moving towards a more 3D geometry so the average radius approximation gets harder. It'll probably still be okay, though, with wedge-shaped magnets.
 
Thanks Eric, that's great. :D

Shall I do a set of 3 DXFs for the new core?

Do you think the reduced cross section (approx 1/3rd for <1 mm), where the two coils are connected in the middle, will cause any problems?

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Miles said:
Do you think the reduced cross section (approx 1/3rd for <1 mm), where the two coils are connected in the middle, will cause any problems?

I seriously doubt it. We won't be coming anywhere near the level of current where that would act like a fusible link, and it's such a short segment that the increased local heating should dissipate quite well into the rest of the coils. I doubt there will be any noticeable impact at all.

Miles said:
Magnet shape modified to give a more equal flux density across the laminations.

This actually won't matter. I can't demonstrate this without full 3D modeling, but the flux won't be limited to just the narrow lower section of the core - it will spread across the entire volume of the core, so any worry about the narrow section of the core saturating first are mostly unnecessary.
 
rhitee05 said:
Miles said:
Do you think the reduced cross section (approx 1/3rd for <1 mm), where the two coils are connected in the middle, will cause any problems?
I seriously doubt it. We won't be coming anywhere near the level of current where that would act like a fusible link, and it's such a short segment that the increased local heating should dissipate quite well into the rest of the coils. I doubt there will be any noticeable impact at all.
Great! I was just worried that there was some effect that I hadn't considered.

rhitee05 said:
Miles said:
Magnet shape modified to give a more equal flux density across the laminations.
This actually won't matter. I can't demonstrate this without full 3D modeling, but the flux won't be limited to just the narrow lower section of the core - it will spread across the entire volume of the core, so any worry about the narrow section of the core saturating first are mostly unnecessary.
I guess I just assumed that it would stay separated because of the reluctance of the inter-laminar insulation. Or, do you mean that it spreads across only as each lamination approaches saturation?
 
One thing that occurred to me, looking at this pic.... Why don't we pack more copper in (or add more iron) until the coils meet (not electrically!) and then, if necessary, ventilate the inside, axially....? Better not to generate the heat in the first place.....

Still got to get the termination wires out somehow, though..... :mrgreen:



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Miles said:
Just wondering if it would be feasible to laser cut the laminate stack....?
I got in touch with Polaris Laminations (recommended by Biff). They can't cut stacked laminations but don't seem to have a problem with cutting and assembling the 70 different lam sizes to make each module. :shock: They stock Arnon 7 NGO steel http://www.arnoldmagnetics.com/Non_Grain_Oriented_Electrical_Steel.aspx No GO steels, though.
 
The biggest challenge is likely going to be maintaining the axial gap (bearing system):

"The bearings were absolutely critical to enabling the modular design of the Yokeless and Segmented Armature [YASA] motor that we helped to design with Oxford," says Nick Carpenter, technical director at Delta Motorsport. "Ultra Low Energy Vehicles, such as the E-4 Coupe, rely on lightweight components to compensate for the inherent problem of the low energy density of lithium batteries when compared to gasoline.

When I first came up with the idea of the new bearing arrangement that would help to optimise the space available for the stator, while accurately controlling the air gap to the rotors, I almost dismissed it, due to the fact that standard bearings would have been too big and too heavy. However, following detailed discussions with Schaeffler UK, the company's engineers were able to offer a special design of hybrid double-row angular contact ball bearing, which has a split inner ring that was able to meet the demanding criteria of reduced weight and cross-section."

This was the breakthrough that Delta Motorsport needed, if the company was to fulfil its ambition of developing a highly efficient plug-in battery electric 'car for the people' that is both stylish in its design and financially viable, but also capable of overcoming the 'range anxiety' perceived by many purchasers of all-electric vehicles.

As Stewart Davies, senior applications engineer at Schaeffler UK, recalls: "It was a very interesting project to work on, with very demanding criteria to meet. The challenge was to keep the bearing as narrow as possible, in order to meet the dimensional constraints of the design envelope inside the YASA motor, whilst at the same time offering a commercially viable bearing solution within a very tight timescale."

Schaeffler UK was able to supply the first samples four months after it started work on the project. Davies continues: "The initial bearing design concept proved to be too expensive and threatened to jeopardise the project. Following intensive design calculations, we were able to offer a single hybrid bearing that met the key design criteria of high performance, reliability and ease of assembly, but that could also be competitively produced in volume."

One of the problems encountered by Schaeffler's design team was the high seal lip speed. With the bearing rotating at such high speeds, all calculations indicated that the seal would wear out and that the bearing would fail prematurely. By specifying a non-contact shield, this problem was solved. Another advantage of using a non-contact shield is the increased life expectancy of the grease. According to Davies, "a hybrid bearing has all the insulation qualities required for use in electric motors, including low friction, but the non-contact shield has doubled the life expectancy of the grease, which has further enhanced the performance of the bearing"

size:750x500

I would like to see a YASA hub motor :wink:
 
flathill said:
The biggest challenge is likely going to be maintaining the axial gap (bearing system):
I was about to turn my attention to that aspect...... Thankfully, I've got a reasonable amount of space to work within and the forces are quite modest in comparison with the YASA.... :)
 
Miles said:
Miles said:
Just wondering if it would be feasible to laser cut the laminate stack....?
I got in touch with Polaris Laminations (recommended by Biff). They can't cut stacked laminations but don't seem to have a problem with cutting and assembling the 70 different lam sizes to make each module. :shock: They stock Arnon 7 NGO steel http://www.arnoldmagnetics.com/Non_Grain_Oriented_Electrical_Steel.aspx No GO steels, though.

Maybe EDM wire cut for the prototype...not sure with the geometry
http://www.hvwooding.co.uk/motor-laminations
 
flathill said:
Maybe EDM wire cut for the prototype...not sure with the geometry
http://www.hvwooding.co.uk/motor-laminations
I've not had much to do with laser, water-jet or EDM wire cut....

I guess the bonding of the laminations is going to be the critical factor for post machining....

Woodings look to be an interesting contact. I'll get in touch with them. Thanks.
 
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