Jack, thank you,

I've tried substituting A-b-C-a-B-c- in the advanced calculator and it shows .96593 for 14 magnets

I then tried AbCaBc and got .5 and at 14 magnets

The only difference between an A-b-C-a-B-c- and an AbCaBc is the fact that the first stator has 6 unwound teeth between the wound teeth, while the other lacks those unwound teeth.

If we saw off the unwound teeth we have theoretically converted one to the other.

So in practical terms what does this mean for thrust and efficiency of a particular motor as a whole?


Edit:

I'm going to throw out a pure guess here.

It does effect the performance because the 180 degree opposed tooth does have a magnetic field, polarized opposite to the pole at the tip of the wound end.

Greg,

Thanks for reminding me of something I have totally forgotten. When you say:

"..By winding 3 slot pitch coils, 1.0 winding factor is achieved. It's very common..."

I simply cannot visualize what that would look like. But then, I have very poor math and geometry skills. Any skill I have there is to simply do the work by rote without a true understand of the concepts. Is this document an explanation of what we are talking about on the winding factor?

http://davidsonsales.com/docs_pdf/CoilPitch.pdf

I'm going to print it and read it over and over if it is.

Jack

For those that got involved after the outrunner revolution the common inrunner designs seem foreign. Most inrunner are wound like this. This was the thread. The links to documents are in there.

The document you link gets into fractional pitch coils. This is important to reduce harmonics in large, high power motors, but not important for model size motors.

VTdiy, the thing to keep in mind is that 2 phases are energized in the case of Wye, and all three, though at different currents, with Delta termination. If you look around the stator tooth heads some will be directly over a magnet and some between. If you look at a winding scheme with a low winding factor like 0.5 and pay attention to the states of the armature magnetization you'll see that some coils simply aren't contributing to the torque. The goal is to make all to the work in the same direction. This is winding factor.

Greg

Greg, thanks. That explanation of the winding factor is very clear.

My question though is why the winding factor would be different if you stick an unwound tooth in between every wound tooth of a 6 tooth outrunner, without changing anything else.

Or to visualize that in reverse, why would the winding factor decrease by nearly half if you sawed off every unwound tooth in a 12 pole LRK.

Or does it, in fact decrease by half?

In other words, is the calculator and table wrong about this particular case?

I can imagine that it is correct if the unwound teeth actually contribute to turning the rotor, and incorrect if the unwound teeth don't do anything.

And somewhere in between if they contribute something but are not a fully energized pole.

Well, got just too curious to wait for an answer.

Welded some steel strip stock onto a washer, wound it with some #23 wire I had, and hooked it up to my new resistance tester which is basically a 1 amp regulated current supply. That thing is coming in pretty handy for a lot of stuff!

Then I swept up some iron filings from hack sawing, put a piece of paper over the whole thing, connected a flight battery. Then I sprinkled the iron filings onto the paper.

Here's what it all looked like.

From here looking at the real thing it looks like the major field is near the wound end, and a lesser field is at the unwound end 180 degrees opposite. I don't see anything at 90 degrees.

It would have been better to have finer iron filings and/or a stronger field with more winds or more current to really make it apparent what is going on. It's possible there is a small field at 90 degrees or along the circular portion. Also it would have been better to use a semi-tranparent sheet instead of paper, so we could see where the poles are. For instance, the left side pattern could either mean a single pole, or two poles very close to eachother, depending on the location of the coil in relation to it.

But at least I can see that it is likely a wind-less tooth opposite a wound tooth has a magnetic field, in a 12 tooth LRK wind. So removing the wind-less teeth would reduce the effective number of stator fields.

Then there is the consideration that the ESC is monitoring the back EMF to decide the when and if on actually energizing the phases. So on LRK, you'll have two coils 180 degrees apart energized when that happens.

Jack

Yes. And I bet that with more legs, at angles between 90 and 180, or 180 and 270, the induced fields are spread out and to some degree proportional to their approximation to 180. That's for the DC single phase case.

For a 3 phase multi arm AC case, well, lets just say it's a lot more complicated.

But, I won't be sawing any arms off an LRK, unless there's some other reason to do that besides the idea that the empty arm isn't doing anything.

What exactly it is doing is still open to question, I think.

I don't even know what pole the wound end is in the above simplified DC piece, or whether there are two poles locally at either side of that coil. All I see is a round pattern of filings on a piece of paper -- it could be centered on the coil which would suggest two poles at either end of the coil, or to the left of the coil which would suggest one.

Since a wind-less arm contributes something, whether a help or a hindrance, it does suggest that its optimal shape and mass might be different than a wound tooth. They don't have to be the same.

There is no reason to guess. http://www.femm.info/wiki/HomePage

Greg

very nice

The current Linux test platform is Wine 1.1.18 running on Puppy Linux 4.2.

Amazing -- I'm running Puppy Linux 5.3 with Wine!

http://www.wolfgangengineering.com/Photos.php