If coils are embedded in iron and resin does this increase the magnetic flux?

[marksparks2]

My question needs clarification. Maybe it could be rewritten.
This idea of creating soft magnetic stators has been about here before, but only in relation to replacing laminated steel stators.
Magnetism is not amenable to common sense.
I am constructing an axial flux motor to turn my telescope very very slowly. There are 32 magnets and 24 coils in two layers, nested by bending the ends of the coils. So 48 coils in total. Almost 100% copper fill air cored. 452mm diameter steel disc rotors. It is a 3 phase motor.
I am testing coil and magnet arrangement. I can get 200g force at 190mm from pivot from a rectangular coil. This is 0.38Nm from only about 0.5 watt. Per coil. The arms of the rectangular coil are between opposing ferrite magnets 10mm thick 20 mm x 60 mm. The coil is 8mm thick. The measured flux is about 1200 Gauss in the middle of the gap 8.5mm wide.
This is good and compares with the Planewave commercial mount which uses giant coils and neo magnets on only one side.
I have experimented with transformer steel between each layer of a coil winding. Thinking, why not? Cedric Lynch has steel between the conductors of his distributed winding.
With my test rig it was not obvious that any force at all was produced.
So the magnetic field was effectively shorted magnet to magnet and bypassing the coil wires?
And also a massive attraction between steel and magnets, with only one coil and magnet set, I can only speculate if this would even out and cogging would be minimal.
I connected the oscilloscope to the coil and passed a magnet over it. A twice as strong signal from the steel infill legs, as the plain ends. In a 14mm width of the coil leg, there is 7mm of copper winding and 7mm of steel in total. I should expect much more with the steel?
So how about using iron powder in the resin when making the stator?
I tried posting on the usual suspect forums and got pretty well mangled and closed down for asking a question demanding a bit of fundamental reflection.
Do magnetic lines of flux pass through the conductor, even if a permeable material is adjacent?
I have lots of photos but I'll wait to see if it's of interest as being loosely off-topic.

 

[marksparks2]

Test voltage 1.32v current 0.48 A. Close to theoretical force value.

 

[scianiac]

I have long wondered a similar idea, I've always wondered if you take a normal iron core motor and pot the motor for durability and cooling as is common but you add a magnetic material could you increase the maximum flux density slightly? The thing I was wondering though is all the material that is not in the magnetic loop does that cause issues? I also think iron-nitride powder may be better than iron powder?

Some pictures might help envision your setup. With the iron layered as I think you describe it wouldn't that mean that only some iron is fully utilized, that is the iron on the outside is only inside a few of coil loops. With such a motor design I can see how the cogging may end up greater than the torque and in theory filling the whole thing with magnetic resin would reduce that but not eliminate it and you might end up with more resin outside the coils than in, again I'm guessing at what your coils even look like based on your description and that might be an issue.

 

[marksparks2]

Many thanks for reading the thread question and I'm now posting some photos which may assist.
I would only use iron powder in the resin that is on the active legs area of the stator. Now that is one advantage of magnetic composites.
If one makes a solenoid with a steel tube on the outside of the coil and nothing in the centre?
Often windmill generator making references show an oblong magnet positioned in the centre of an air cored coil - which is odd. There is no force generated in that orientation unless there is a permeable magnetic core. Like a Yasa motor. It is only the two active legs of an air cored coil that interact with the magnetic flux. Now why does the core not short circuit the flux between the magnets? Ha, I can't answer.

 

[amberwolf]

Moved thread from Forum Rules and Features (why post a motor question there?) to Motor Technology. Please check which forum you're posting to before doing so.

 

[marksparks2]

Yes thanks. When I was posting I had just read the rules, and then looked for a menu of different categories, didn't seem to be a list anywhere. Neither could I move it myself when I realised the existence of the motor postings.

 

[marksparks2]

To give another perspective, considering an axial flux motor with a serpentine winding.
There are no individual coils as such. There's nothing magical about coils, it's just practical and well studied?
A Yasa motor uses edge wound rectangular copper conductors, beautifully neat as you can see on YouTube videos of the winding machines.
CAM would easily make a serpentine coil in a similar way.
In my case that is tricky winding 221 turns for each phase with ordinary round wire with no errors. And the folding of the end turn sections requires a full motor size complex jig.
Although I can achieve 100% of the fill possible with circular section wire, there's still a lot of space empty which could be filled with a magnetically permeable material. Better heat conduction. It looks like the only way to find out is to make a complete motor stator. The rotor plates are mounted directly to the telescope mount. That is a lot of work for an unknown experiment. It would be ok if there wasn't much torque improvement, but a disaster if it turned out the resin and iron powder shielded the conductors and it was worse than just being air cored.

 

[marksparks2]

It needs a real Professor to ponder this. Maybe I'll write an unsolicited email to one and post the response back here for future reference by motor builders.

 

[marksparks2]

I've sent off a university professor enquiry.
It also occured to me that ferrofluid is used where a coil is in a magnetic air gap, loudspeakers is an example I've experience of. It doesn't stop them working.
Obviously an EV motor spins at high rpm and that's not good for fluids.
I've got samples but not litres of the stuff.
Basically this question could be re-phrased. 'if I drill a hole in a piece of iron between two magnets to poke a piece of conductor and pass a current through it, does the wire know it's in a magnetic field and experience a force?'
I also suspect from evidence posted on YouTube where a Gauss meter gives less flux on magnet surface than vendor claimed, that a drop of ferrofluid was used in vendors or manufacturers testing. Even 0.5mm is a long way in air for high intensity flux from the actual surface of a neodymium magnet.

 

[fechter]

Adding iron powder to the stator core will definitely increase the flux, but not as much as laminated steel.
The attraction between the core iron and the magnets will be very strong and tend to cause parts to flex. Things need to be really stiff.

Ferrofluid is pretty weak at conducting magnetism. Better than air, but way less than solid iron. I use it in one of my bike motors for stator cooling.

Any conductor with current flowing will experience a force in a magnetic field unless the current is flowing parallel to the field.

 

[marksparks2]

@fechter yes the elimination of the air gap is what I've now read is the main reason to use ferrofluid. The attraction to the magnets just serves to keep it in the motor hub. Any oil would do but would be flung everywhere. It's a bit like silicone heat sink paste, somebody tried toothpaste and it was just as effective.

 

[fechter]

You might want to check out some of these topics where guys have built axial flux motors. Some are 3D printed:

Axial flux motor topics

 

[marksparks2]

@fechter thanks, I've been entertained for years with these.
The neatness of the windings is a major influence on efficiency. The Golden Motor 3kw AFM comes in variants, one dismantled on Facebook has super neat single heavy guage copper coils, machine wound. The one featured here has a rats nest of Linz imitation crudely hand wound.
DIY cannot compete with a R&D. All the more remarkable that Cedric Lynch introduced his radical successful solution.
The government is going to destroy the e-bike on public roads in any case.
My motor is generating a rotary force at zero rpm, rather than torque as such. To match earth's rotation, for hours at a time and able to put out a short peak power if there is a gust of wind. It might be open to something radical.

 

[marksparks2]

I've carried out an experiment with the Gauss measured in a hole bored in a block of iron, fitted between the magnets. It measures about a third of the flux.
With two 8mm by 8mm lathe tool cobalt steel blanks, in the slot between them the flux is about a half.
I'm using a SS49E which can read linear to +-1000 Gauss, thereafter Gauss guessing. These ferrite magnets I got in the 1980's in boxes of 100 for a few pounds.
The maximum response, heavily non linear, of the 49E is 1400 Gauss. I get the output flat-line measured in the 8mm gap of my test rig, so the flux must be at least this. The back iron plate is only 2mm and a steel object shows plenty of flux leaking.
They're nothing special, maybe used in old cigarette vending machines to stop people putting in washers. I took a machine dumped in the street apart once out of curiosity.
So there you go. Iron short circuits the field around a conductor, but in a half hearted way. I won't bother with magnetite infused resin or whatever.
Just wind the coils perfectly.
Now I'm checking their inductance and how it will affect PWM etc. 2mH each, 16 per phase in series. Each phase independently driven by full bridge.
PWM about 700Hz. Only 45 data points per second on a 16 bit sine wave.
A nice motor for someone who likes slow living.

 

[marksparks2]

To add, the inductance of the coil shown in my original post , with the transformer steel inserts was only 500uH. It did have less turns,by about 30%, and was a pita to wind and glue each layer. But that lower inductance was a genuine surprise, I mean it weighs a ton more than the only copper coil.
Now if anyone has a Lynch motor to test, what is the performance without the steel wedges between each leg of the single turn coils? Mysterious magnetism.

 

[marksparks2]

In Faraday fashion, there is another variation I might try.
If I can work out a way to actually wind it.
Put steel between each flat coil that makes up the rectangular/trapezoidal coil. With a ferrite composite material, this would be a bit more manageable. But still tricky if it's not to ooze out in the wrong place.
The flux never has a greater air gap than the diameter of the wire. I have several EI steel thickness, from .22mm to .5mm.
The Yasa and other high performance motors use moulded ferrite composite, but obviously at 29,000rpm eddy currents and hysteresis are a major design factor.
The flat wire they use would be easier to put steel between, sometimes only one layer is used.
The designers have the software to model the possibilities I propose.