DIY Toroidal Axial Flux PM

[TorontoBuilder]

Yes, IMO for such parts small milled glass fibers are much better than laid sheets. These fibers are used to make epoxy resin for structural fillers and filleting components. They work very very well, but you need to have respirator, gloves and avoid contact with the fibers since they will irritate the skin like crazy.

I also dont think that a stator for a motor such as yours even needs the additional reinforcement, but it can't hurt to add glass fibers.

Additionally, you can add powders to significantly increase the thermal conductivity of the stator. I'm sourcing industrial grade silicon nitride powder to add to the epoxy I will use on my stators.

[Jrbe]

I'm glad you're not giving up.

I think a silicone mold would not work out very well if you're clamping it. I'm not sure how much force you're using but ideally you should look at using something that won't deflect much to at all at that pressure. Your clamping deflection will end up your thickness variability. Maybe a .25 - .5" piece of steel or aluminum top and bottom.

There are thermally conductive potting epoxies available. Not sure how much strength you would need - if is worth finding a high strength and thermally conductive epoxy. You likely have some voids that you could lace fiberglass around in a star shape between coils to help along with maybe adding it in with the wire.

[TorontoBuilder]

I've used silicone moulds with lids and a couple small overflow holes with light pressure to hold the lids on to create a consistent dimensional shape when making multiples of the same part, but yes, if the stator windings need compressing then silicone needs to be replaced with a more rigid mould or it needs to be combined with another technique...

I make micarta laminate blanks out of used levis jeans using a vacuum bag material placed between two flat bars 1/2" thick with a piece of 1/4" plate and some added weights used to span the width between the two bars to compress the blank to the desired 1/2" thickness. The excess epoxy is squeezed out to the sides.

A silicone ring could be used with this technique to provide the stator shape. The ring could be made slightly proud of 1/2" and it could compress to the desired dimension, as would the stator windings.

[APL]

Teflon doesn't stick to anything too,. can be ridged in thicker forms, but comes in thin adhesive backed sheets as well,
maybe good for a liner. Just a thought. (don't ask me how they get adhesive to stick to it)

There are a lot of Hi tech-ish epoxies that will probably fit the bill, but the cost can be very extreme $$$ and usually
need an applicator gun and mixing nozzles as well. Trying to find one that's cheaper and works well involves trial and error,
which in it's self is expensive.

https://www.mcmaster.com/epoxies/

[TorontoBuilder]

Yes you can buy high thermal conductivity epoxy, but you can likely make your own for far less if you dont need to meet a published standard... which we dont.

[Hummina Shadeeba]

If you get a one-part epoxy you bake later you have no rush. Adding filler to make more thermally conductive it can get very thick and will need to vacuum it in

The insulation on the wire is stretchable and square magnet wire is formed as round and then squeezed into shape; maybe you could get a lot more copper in and squeeze it into form.


Maybe could crush/glue all the wires against aluminum plates to transfer heat?

[TorontoBuilder]

I've never used a heat cured epoxy, none of my projects ever had the need. Then again I've never wanted to bond metal with a high strength adhesive, preferring brazing or silver soldering.

Do you have a source of square magnet wire Hummina? I've not been able to find any myself here in Ontario.

The stator I am designing will act as heat sink to draw heat from within the motor. The outside of the stator will have a groove with active cooling coils, and that holds the outside edge of the stator coils, and will be filled with high thermal conductivity epoxy made with alumina powder.

I'm opting for vacuum bag material to surround my mould since my pressure pot is not large enough, but I'll first degas the resin/alumina mix.

The coil connections will all be set in the same material on the inside of the coils.

[Hummina Shadeeba]

O I didn’t realize the stator would be steel and thought it was coreless.

Square wire is ridiculously expensive. I managed to squeeze some samples out of them but if ur using anything thinner than maybe 16 or 15 awg it’s almost impossible to utilize its benefit as it’s so hard to keep face on face and keep it from twisting.

https://mwswire.com/magnet-wire/square-magnet-wire/

The wire was a disappointment but I called them on the phone unrelated to the square stuff and just about how crushable their insulated wire was and that was the biggest revealer as no matter what obstacle I laid before them they said no problem. I bet you could practically fill the whole stator slot if u had a way to crush it in there

[TorontoBuilder]

For clarification, my stator i will be comprised of stamped copper coils (1.6 mm thick), with laminated wedges between the coils and maybe some laminations thru the coil core. The stator will have inner and outer ring structures to fix the geometry of everything to be perfectly concentric with the motor spindle... all fixed in position with epoxy

[HalbachHero]

I don't have too much of an update. Had family visiting and other priorities.

I have been battling my printer non-stop, but I think I'm winning. I think...
Otherwise, there are a couple things I am working on.

I made something to test coils and their proximity to the edge of the magnets. I made a modification recently to the stator to reduce the OD since it extended beyond the edge of the magnets, and it made me wonder how critical that actually is. the goal of the test is to optimize the size of the coil, ideally I want to know what the max OD and min ID of the stator could be. assuming the magnets are interacting with the coils even beyond the edge, I should be able to squeeze out a bit more juice from the same thickness and magnets. I realize the the optimal will likely be when the coil lays just beyond the magnet's edge, but im really looking to see how far away there is still a reasonable interaction.

I made the tool, just need to test it and log the data.

resized-image-Promo - 2021-11-02T161229.297.jpeg (114.54 KiB) Viewed 546 times

The other piece I have been working on is the winding jig. I made the modifications I wanted and just got it all finished up. I ordered some braided nylon cord to test winding, but I don't think I bought enough. Should have another update soon

resized-image-Promo - 2021-11-02T162421.485.jpeg (112.33 KiB) Viewed 546 times

[TorontoBuilder]

Nice

[Jrbe]

There are a bunch of 3D printed motor ideas here. Probably worth a read. https://www.instructables.com/600-Watt- ... ss-DC-Ele/

Also they listed iron filled filament in there for the stator core. https://www.proto-pasta.com/products/magnetic-iron-pla

You could also optimize some of your motor parts to bring all of the material in as far as sensible and thin the bolt boss some

resized-image-Promo - 2021-11-02T161229.297.jpeg.jpg (28.51 KiB) Viewed 495 times

Is that glue sticking well to the plastic?

[HalbachHero]

Alright, time to play a little catch up.

Yes, IMO for such parts small milled glass fibers are much better than laid sheets. These fibers are used to make epoxy resin for structural fillers and filleting components. They work very very well, but you need to have respirator, gloves and avoid contact with the fibers since they will irritate the skin like crazy.

Thanks, I will try it and see if there is a difference with the fibers. I am certainly familiar working with fiberglass insulation, and the irritation that comes with that. I will definitely wear a respirator, and do it outdoors. its getting chilly though!

Additionally, you can add powders to significantly increase the thermal conductivity of the stator. I'm sourcing industrial grade silicon nitride powder to add to the epoxy I will use on my stators.

I know nothing about the additives. I will look into this. I do have concerns about wicking the heat to the exterior of the stator. Obviously that will be close to the magnets. I used N52, which was probably foolish due to the low demagnetization temperature. I wonder if a thermally conductive resin would increase the heating of the magnets.

I think a silicone mold would not work out very well if you're clamping it. I'm not sure how much force you're using but ideally you should look at using something that won't deflect much to at all at that pressure. Your clamping deflection will end up your thickness variability. Maybe a .25 - .5" piece of steel or aluminum top and bottom.

I initially agreed with this, but the more I thought about it, the less I am convinced. I was thinking a shell with a thin layer just to help with the mold release.
I was also thinking similarly about the deflection of the shell. I think something rigid like what you suggested is a good idea. I might be able to piece together something

A silicone ring could be used with this technique to provide the stator shape. The ring could be made slightly proud of 1/2" and it could compress to the desired dimension, as would the stator windings.

Yeah this is a great idea. This would really simplify things when it comes to having a bit of variation predicting how much it will actually compress. I think it could lead to deflection in the resulting stator, but ideally I think that comes down to how I squish it all down, and the rigidity of the shell of the mold

Teflon doesn't stick to anything too,. can be ridged in thicker forms, but comes in thin adhesive backed sheets as well,
maybe good for a liner. Just a thought. (don't ask me how they get adhesive to stick to it)

I haven been thinking about this suggestion a bit. I think I could use something like this in the jig to keep the wires from getting caught on the fins. It would make removing the wire afterwards much easier. Also could be useful in protecting the wires in the event I add laminations to the stator at some point.

There are a lot of Hi tech-ish epoxies that will probably fit the bill, but the cost can be very extreme $$$ and usually
need an applicator gun and mixing nozzles as well. Trying to find one that's cheaper and works well involves trial and error,
which in it's self is expensive.

I have a 50mL applicator gun, it works wonders for making the rotors, but I have just been using cheap Scotch Weld DP110 and the high heat Permatex stuff (I cant use that one in the applicator though)

I bet you could practically fill the whole stator slot if u had a way to crush it in there

This would be the ultimate goal. I understand that the round wire leaves some gaps. This is another reason I opted for the small thickness (32AWG or ~0.2mm) I could probably get away with using thicker wire, It might be actually easier to work with in that it would hold its shape better when crushed together. I've looked into square wire as well. It was certainly more expensive, and I think there's diminishing returns at smaller gauge, as the round wire is more efficiently packed the smaller you go.

Does anyone know if there is some standard to follow for using multi-stranded wire as I am. My understanding is that it helps with losses in high frequency operation, and knowing that I was going to have I high pole count, I went with some pretty thin stuff.

There are a bunch of 3D printed motor ideas here. Probably worth a read.

Thanks for the link. I have seen that project, but not that link specifically. That man is very thorough with his work. I might tediously select my magnets the way he did in one of these versions.

Also they listed iron filled filament in there for the stator core. https://www.proto-pasta.com/products/magnetic-iron-pla

Yes, this stuff is cool. I actually have a spool of it here. its 13% iron, and wears out your nozzles like theres no tomorrow. I have a hardened steel nozzle, but was not able to get it to work, never figured out why.
Also, I think I am probably not going to go back to 3d printing the stator. I think that the plastic is just too flexible. But it might make okay laminations. Ill hold on to it for down the road.

Is that glue sticking well to the plastic?

Yeah its just hot glue, I am only checking back EMF to measure relative differences, its not getting warm at all, and there's only 2 turns per pole.

You could also optimize some of your motor parts to bring all of the material in as far as sensible and thin the bolt boss some

Yeah ideally I would love to lose mass and/or overall OD. I think thats where I could reduce inertia the most, if anywhere. Which is part of why I started doing this test in the first place. The stator's end turns currently extend beyond the edge of the magnets. So I would love to know if there is a gain or loss by moving things closer or further by 1mm steps.

The results are in!

Let me preface this by saying that its a little skewed and misleading due to the back iron behind the rotor magnets. The magnets on the ID of the rotor do not have metal going all the way to the edge of them, however the OD does. Also, I'm sure this is something that could be measured with simulations. But I wanted to make something real, and have an excuse to use my scope some more.

Here's the test setup. I clamped the stator in place, had all the tests labeled and had a machine screw tightened in place on the rotor to spin it with the drill.

resized-image-Promo - 2021-11-08T221459.620.jpeg (106.41 KiB) Viewed 441 times

This worked well, but I found that test B was giving me weird results on the scope, I'm assuming there was some exposed wire somewhere intermittently shorting things out, but I'm not really sure, I just decided to skip that, and for symmetry I skipped the similar test on the OD.

I used Test A as a baseline which was a 0mm offset from the inner edge of the inner and outer end turn. (all test measurements are peak to peak voltage in mV)
Test A(CH1), C(CH2), D(CH3), E (CH4)

resized-image-Promo - 2021-11-08T221527.948.jpeg (121.3 KiB) Viewed 441 times

Test A(CH1), H(CH2), G(CH3), F(CH4)

resized-image-Promo - 2021-11-08T221554.680.jpeg (120.91 KiB) Viewed 441 times

Screenshot 2021-11-08 233631.png (14.79 KiB) Viewed 441 times

So keeping in mind that the inner diameter is lacking back iron to the edge of the magnets, its easy to understand why it tapers off as you move away from the edge. However, the OD test was a little counter intuitive for me. The voltage was slightly higher when you moved away from the edge of the magnets. My tests only went to 4mm, so I'm curious where the optimal is, but unfortunately this would mean larger OD, more wire, leading to higher overall resistance leading to losses to heat, and just more material and weight.

So the takeaway... I think I need to make better rotors using the new back iron that I got laser cut. which will have back iron to the edge on both the inner and outer diameter, then re-test. But its looking like there is a slight gain, from moving the wire away from the edge of the magnet, but it seems like a negligible increase. and I think quantifiably not worth it due to the other losses incurred.
Measuring heating alone. It might actually be worth it. At reasonable values the loss from heat becomes pretty small, and pushing kV down seems to help keep those values low. This is also not very accurate though, because the temperature would certainly be over 20*C and would climb quickly given the wires were all bundled together and potted in epoxy, obviously increasing resistance, and in a negative feedback loop, contributing to more heat.

Screenshot 2021-11-09 002230.png (15.79 KiB) Viewed 441 times

Screenshot 2021-11-09 002250.png (15.6 KiB) Viewed 441 times

Screenshot 2021-11-09 002312.png (15.9 KiB) Viewed 441 times

Lots to think about here....

[Hummina Shadeeba]

The field comes out on the sides of the magnet so iron directly behind a magnet does little. You could cut weight this way. This goes up to 3mm thick and down to 1 and catches almost all the field.

I bet the benefit of a good back iron trumps any details between wire thickness and fit abs will drop the kv substantially

[HalbachHero]

The field comes out on the sides of the magnet so iron directly behind a magnet does little. You could cut weight this way. This goes up to 3mm thick and down to 1 and catches almost all the field.

The magnets I have are all bar magnets but magnetized on the large face, not on the ends. I have done simulations in FEMM to optimize using only as much back iron as needed. I found that given when using the halbach array, the back iron requirements are less to achieve 0 leakage.

given the size of my magnets, I found ~1.5 mm was optimal. This is currently what the back iron is, but it simply does not cover all of the magnets. I had some steel custom laser cut and intend to make a new set of rotors that are hopefully more rigid with less leakage. Hoping to make those soon

[Hummina Shadeeba]

i mean when magnetized on the large faces as normal for a motor the field lines come off the edges.

[mxlemming]

That looks ridiculously sinusoidal. Can you press the math button on your scope and see what the harmonics come out as?

Nice colors. Just need to add some red filament

[HalbachHero]

i mean when magnetized on the large faces as normal for a motor the field lines come off the edges.

Hmm, I dont think I am understanding what you are saying. My understanding of the source of magnetization is the alignment of the polarity of electron spin, which occurs at the atomic level. This fundamentally would lead to the entire material acting as a magnet and the field line origination from every point of the magnet at once and finding the path of least resistance to the opposite side.

Could you please explain this phenomenon or provide a source please? If what you say is true I agree. There may be room for further optimization/ weight reduction.

That looks ridiculously sinusoidal. Can you press the math button on your scope and see what the harmonics come out as?

I'll admit, I don't really know what im doing, but this look pretty clean to me.
avg set to 20. using FFN, and hamming, and dBVRMS

resized-image-Promo - 2021-11-10T224706.567.jpeg (123.13 KiB) Viewed 344 times

The photo captured the wobble in the rotor as the display was updating, which I believe is why is looks like there are two yellow lines at points.

Nice colors. Just need to add some red filament

Ha, yeah its one step away from being patriotic, but I think Im more of a two tone kind of guy.

[HalbachHero]

Mxlemming,
Keep in mind, this is only from me spinning with the drill, and this is still using the testing thing I created, not a stator. However the testing thing was made to match the spacing of the stator, with the only variable being the length of the legs, and starting/ending point of the end turns

[Hummina Shadeeba]

I thought a motor without iron in the stator would normally produce a sinusoidal back wave




https://www.kjmagnetics.com/blog.asp?p= ... fields-101

[HalbachHero]

Hummina Shadeeba,
This is fascinating. I have not heard of this before. Thanks for sharing, I certainly have some reading to do. My first immediate thought, is why are magnets not created with a series of fins, or ribs on the faces, would that not in theory provide stronger points across a surface?
I would assume something like that is harder to manufacture/magnetize though.

Another thought is how would you optimize that? It seems like you could put small pieces of iron to "bridge" the large faces. Given the size of the halbach magnets on mine, I would probably consider just attach that to the middle of the bridge. I also wonder how much thicker or thinner the iron would need to be to prevent leakage.

Cool stuff. I think there's an experiment to be made here

[fechter]

The shape of that curve will change dramatically when there is back iron or stator iron.

[TorontoBuilder]

The shape of that curve will change dramatically when there is back iron or stator iron.

Correct, timely and succinct point.

If I am not mistaken, much of the cutting edge electric motor research is in relation to hybrid rotors and complex 3D flux paths which is only possible because flux can be manipulated by components external to the magnets.

now HH's reading load has increased exponentially

[mxlemming]

Hold on... To derive meaning from the flux density of a magnet in free space at the surface is going to lead you to ask kinds of misunderstandings. The surface flux at the edges gets stronger because the permeability of the magnet is higher than the air so the flux takes a path through the magnet in preference to through the air. The shortest path considering the permeability to close the flux lines goes through the magnet

As soon as there's any metal, other magnet etc near it, this surface flux measurement goes out the window.

There's absolutely no reason for a motor without iron to be perfectly sinusoidal. The BEMF is due to the copper cutting flux lines. If the magnets were wider spaced and there were big areas without flux then clearly the BEMF would not be sinusoidal.

[mxlemming]

The shape of that curve will change dramatically when there is back iron or stator iron.

Correct, timely and succinct point.

If I am not mistaken, much of the cutting edge electric motor research is in relation to hybrid rotors and complex 3D flux paths which is only possible because flux can be manipulated by components external to the magnets.

now HH's reading load has increased exponentially

I'm pretty sure most cutting edge motor research is related to bogus claims of micro optimisations and creative accounting of mass, power and cooling mechanisms.