PM motor stator design

[magnusrm]

Hi guys.
Im working on a project to make a new DC underwater thuster where we are making the stator / rotor ourselves.
As im a mechanical engineer, this is not my field of expertise and my customer prefers just to try out the mechanical concept before we spend money on el-mag optimizations.
As of now, the thought is to use 24 tooth stator and 28 magnets to reduce cogging.

The stator has to be as lightweight and compact as possible. It is now Ø 140mm internal, Ø 151mm external and 10mm high. We are going to mold in the stator and rotor in order to waterproof it. The air gap will be 2mm, as we have to over-mold with a minimumthickness of 0,5mm, and have 1mm space for debris / dirt to pass through without any jams.

I have tried to reduce iron loss based on the knowledge I have, but I have not done any FEA.

What do you think of this stator design? Any other tips?

Thanks a lot!

 

[magnusrm]

Dosent anyone have some input on the general geometry? Not expecting any analysis, just if it will be ok based on your experience.
thanks

 

[electricpete]

I work only with large motors, and not a motor design engineer either. So my input, not worth much.

The things that strikes me is the back iron is exceedingly thin compared to what I'm used to. I realize there are flux density reasons for this:
[*]In large motor with several slots per pole, flux from several teeth flows together at a given location in the backiron. So backiron depth larger than tooth width.
[*]In your motor probably the polarity of current in slots alternate, so a given location in the back iron probably carries only half the flux of a tooth. And my eyeball says to backiron depth is approx half the tooth depth.

Also I notice in your backiron there are divits on the OD where flux would not be flowing. So in summary it looks like your minimum backiron depth is driven by soley flux density, resulting in very thin backiron. I just wonder to what extent mechanical considerations were considered in design of the backiron. Textbooks show a classical analysis done examining the bending modes of the stator iron to see if any might match the magnetic excitation (in frequency and shape), similar to figure 4 here:

http://www.industry.usa.siemens.com...uments/magnetic-noise-in-induction-motors.pdf

I tend to think we are more likely to get unlucky hitting a resonance for flimsy structures with many high-order bending modes to consider. I don’t know to what extent support is provided to backiron by the frame.



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(2B)+(2B)' ?

 

[magnusrm]

Hi. Thanks for your reply.
You are right, the backiron is just a tiny bit larger than half the tooth (4mm backiron / 7mm tooth). Each tooth will have one pole.
The stator will be pressed into a aluminum casing and then molded in by a thermoset polymer after the windings are in place, so it will be pretty well fixed.