Dual rotor axial flux motor design

[Miles]

Finally you started this , i think aial flux design is underrated today . i bought axel borg book - diy - nice chapters there - you should look it up . Laters Axel design was based on dual rotors with mags i think

Thanks Marko. I'll look it up.

[Miles]

How about the possibility of using some kind of reinforced ceramic for the core module supports? Or engineering plastics?

[rhitee05]

Any concerns about flux lines cutting through at an angle to the lam stack, as the lam stack isn't curved but flat?

I suspect that this shouldn't be too significant so long as the pole count and radius are sufficiently large, so the angular size of each core is not very big. Looks like maybe 18 teeth/cores? Since Miles knows the dimensions, I'm sure he could figure out how much of a difference there is between the straight lams and the ideal arc. Probably not worth the trouble to do anything about, especially if the lams are made from thin electrical steel.

I was also going to suggest that it would probably end up being worth your while to shape the cores so the center section is narrower and the ends flare out somewhat. That would give you room for more copper in the winding while keeping the tooth ends the same size, which I suspect is a good tradeoff for slightly lower saturation flux threshold. This is a good item for some simulation and optimization.

If you wanted to be really fancy, you could shape the ends such that the flare is wider on the outside edge of the core and narrower on the inner, making the end somewhat more wedge shaped (looking axially). Again, not entirely certain how much benefit this would provide (this is a 3D geometry, so would be difficult to simulate using the freeware) and would make fabrication more difficult.

[Miles]

It's only a 90mm motor. The minor diameter across the cores, as modelled, is 62mm. Major diameter 82.

Maximum deviation is 0.4mm across 10mm wide core.

[Miles]

If you wanted to be really fancy, you could shape the ends such that the flare is wider on the outside edge of the core and narrower on the inner, making the end somewhat more wedge shaped (looking axially). Again, not entirely certain how much benefit this would provide (this is a 3D geometry, so would be difficult to simulate using the freeware) and would make fabrication more difficult.

I seem to remember modelling something like that on the single rotor design. Unless there's a significant gain it would be nice to keep all the laminations identical. I should imagine it would be more beneficial if you were using SMC cores?

[rhitee05]

I seem to remember modelling something like that on the single rotor design. Unless there's a significant gain it would be nice to keep all the laminations identical. I should imagine it would be more beneficial if you were using SMC cores?

Come to think of it, you might actually be able to use the square ends as a "feature". I expect this would have the effect of making the BEMF of the motor more sinusoidal, especially if you also used rectangular magnets on the rotors.

[Miles]

Thanks Eric.

Anyone know how much there is to be gained from using grain oriented steel for this application? It would certainly be possible to take advantage of it with this type of core design.

[Miles]

Any concerns about flux lines cutting through at an angle to the lam stack, as the lam stack isn't curved but flat?

I suspect that this shouldn't be too significant so long as the pole count and radius are sufficiently large, so the angular size of each core is not very big. Looks like maybe 18 teeth/cores? Since Miles knows the dimensions, I'm sure he could figure out how much of a difference there is between the straight lams and the ideal arc. Probably not worth the trouble to do anything about, especially if the lams are made from thin electrical steel.

It's only a 90mm motor. The minor diameter across the cores, as modelled, is 62mm. Major diameter 82.

Maximum deviation is 0.4mm across 10mm wide core.

This is what it looks like with a 0.35mm lamination thickness (first two laminations from the inside):

[Miles]

At worst, a 1.5% increase in "effective" lamination thickness (2.25% hit), on entry and exit..... So, less than 1% increase in eddy current losses from not having curved laminations?

[kenkad]

rhitee05
Why do the laminations have to be horizontal (as Miles has shown) rather than vertical. The first application of the split flat coil wrap that I ever saw was done by Shane Colton. Is there any benefit in making the coil end plates more 'pie' shaped to maximize the flux face area of the coil? Does this approach not engage the rotor magnets for a slightly longer period of time and result in a more sinusoidal BEMF? I have not yet had time to start my axial design, but I had assumed that a powdered core with intergal flux face plates could be all ground at the same time on a lathe fixture to ensure that the resultant gap between the coil flux end plates and the rotor magnets is more uniform/constant as opposed to using laminations. Miles, have you considered how or what would need to be done to replace any coil if it is damaged in any way? How do you plan to connect the various coils and ultimately bring out the wiring? Is this a single 3-phase or multiple 3-phase groups? Very glad to finally see a discussion like this ongoing. Thanks everyone for answering.
kenkad

[Miles]

Hi Ken,

I'm not sure what you mean. The laminations run in the direction of the flux path.

Even the best powdered core material wouldn't give as high a performance as decent laminations (unless there's a significant advantage to a non-planar flux distribution).

With a laminated core, would there be any advantage to having a proportionally greater face area, per lamination, if the main part of the core is uniform? The flux at entry is confined within that lamination.

The windings exit on the outside, through the case, and will be joined there.

The idea is to engineer it so that the pre-wound stator modules can be inserted through case, so they could also be replaced that way, too.

[Arlo1]

I like it I plan to build something like it but multi layered one day.

[Lebowski]

I don't know what you mean with laminations, is that the laminated iron core of the coils ?

The motor I built myself is also an axial flux, I have no iron in it which makes it possible to spin
this motor using only 30 milli-Watts.

I've thought about adding iron, what I would do is get plastic coated iron wire (like they sell at the garden center
for tying up beanstalks). I would wind this (soaked in epoxy) to the desired shape / diameter. I think this
would be a very good design for having low eddy currents, there is no continues loop except within a
sideways cross section of the wire. But because it's wire the sideways cross section would be very
shallow...

A mayor disadvantage of iron core (and the reason why I don't have it) is that the two magnet
plates in my design would attract each other with a lot of force making it almost inpossible
to take it apart again. Currently (with the 7 mm airgap) the force is about 100 kg, taking it
apart requires a bearing puller type tool but is still possible...

About airflow to cool it, with mine there is a detectable flow of air being sucked in the core
and flying out inbetween the magnet plates and coils (flow due to centrifugal force).

I already got the magnets and a second coil plate prepared for a dual layer design but at the moment
I'm concentrating on getting my controller IC finished....

DSC00299_scaled.JPG (148.47 KiB) Viewed 299 times

[Miles]

I don't know what you mean with laminations, is that the laminated iron core of the coils ?

The motor I built myself is also an axial flux, I have no iron in it which makes it possible to spin
this motor using only 30 milli-Watts. ....

A mayor disadvantage of iron core (and the reason why I don't have it) is that the two magnet
plates in my design would attract each other with a lot of force making it almost inpossible
to take it apart again. Currently (with the 7 mm airgap) the force is about 100 kg, taking it
apart requires a bearing puller type tool but is still possible...

Yes, the core laminations.

You can get a greater specific torque with an iron core. That's what is needed for the Challenge.

Yes, the attractive force is a big problem. Maintaining a balance between the two airgaps..... The rotors are only 80mm in diameter, though - it's quite a small motor, compared to yours.

[Lebowski]

You can get a greater specific torque with an iron core. That's what is needed for the Challenge.

I looked at it from a different angle... In my opinion you need to convert
electrical power efficiently into mechanical power, independent of whether
you want to race uphill or just ride around on the flat. Core laminations help
with efficiency but only in a certain rpm range (too low rpm -> cogging,
too high rpm -> eddy current losses). No iron core gives a lower specific
torque but this can be solved by chosing a different gear ratio so I wouldn't
say this is a disadvantage of having no iron core.
For me in the end the efficiency with no core was good enough, the disadvantages
of the iron core outweighed its advantages.

[Miles]

I can see that your motor would be more versatile (more efficient over a wider range of torque outputs) but mine is being designed specifically for this: viewtopic.php?f=30&t=14484 In practice, I'll be using mine with a 2 speed gearbox - they are designed as a pair.

[Miles]

This looks to be a useful resource: http://www.emetor.com/

As well as the revamped: http://www.powerditto.de/bewicklungsrechner.html

[markobetti]

Dear Miles, the gearbox isnt published at ES ? Its okay if its a secret , but if not please post link since i havent been able to locate it. i remember you and hal discussion about retro direct drive ....but thats not it right ?

[markobetti]

Maybe you can try your calculations in trial version if they have it :

http://www.infolytica.com/en/products/

http://www.infolytica.com/en/applications/ex0072/

[Miles]

Dear Miles, the gearbox isnt published at ES ? Its okay if its a secret , but if not please post link since i havent been able to locate it. i remember you and hal discussion about retro direct drive ....but thats not it right ?

Hi Marko,

No I haven't published anything about it here. I will but not just yet. It is a retro-direct as Hal and I were discussing then but I've spent ages exploring all the possible options and going through numerous iterations of design.

[Miles]

Maybe you can try your calculations in trial version if they have it :

http://www.infolytica.com/en/products/

http://www.infolytica.com/en/applications/ex0072/

Thanks! They didn't do a trial version before - now they do.

[kenkad]

miles
This is what I meant by vertical laminations, bent into a 'C', stacked, to produce a trapezoidal end. It seems to me that the flux path out the end is now distributed. I used different colors for the lam layers to better see the result. I have never seen a sim of this, but have always wondered why this is not done. My preference would have been to do this as a powdered core so that the center could also be trapezoidal, providing a better motor fill with a split copper strip winding like Shane did in one of his motor experiments. I hope this explains my question to everyone. As to why the more than one 3-phase group question. That is because starting torque requirements to get a vehicle moving are greater than running torque requirements at a speed, so I would op to turn off a 3-phase group to reduce motor power consumption since I do not believe the cogging would be noticeable at speed, momemtum effects.
kenkad

[markobetti]

Glad to be a service to you. You helped me alot, for example with freewheel . Finally made indestructible freewheel with two bearings inside al 7005 mat. and more pawls than any freewheel on the market i can think of. http://img217.imageshack.us/img217/326/heavymetalx.jpg . Logo is covered with white color due to my project that is in state not intended to be shown right now under the name. Anyways , thank you MILES

[Miles]

miles
This is what I meant by vertical laminations, bent into a 'C', stacked, to produce a trapezoidal end. It seems to me that the flux path out the end is now distributed. I used different colors for the lam layers to better see the result. I have never seen a sim of this, but have always wondered why this is not done.

Ken,

I don't think this would work. You would get serious eddy currents on the end face. The laminations need to restrict flow perpendicular to the direction of the rotor. Also, there will be a strong reluctance between the face laminations, I think.

[Miles]

Glad to be a service to you. You helped me alot, for example with freewheel . Finally made indestructible freewheel with two bearings inside al 7005 mat. and more pawls than any freewheel on the market i can think of. http://img217.imageshack.us/img217/326/heavymetalx.jpg . Logo is covered with white color due to my project that is in state not intended to be shown right now under the name. Anyways , thank you MILES

Wow! That's nice Marko. Look forward to seeing what it's intended for....