Hi All,

I'm trying to simulate a magnet motor using FEMM, and I have some basic questions about interpreting the results.

I think my model is telling me the motor should work, but I could use an experienced eye to validate my thinking.

My first question is:

When asking for torque values, does positive torque represent clockwise twist, and negative torque counter-clockwise twist?

When the result says "about point 0,0", are they talking about the 0,0 absolute point on the surface, or are they talking about a new 0,0 point in the middle of the region/block that is being integrated?

Any help would be appreciated.

Yes, the positive and negative torque values equate to the clockwise/counter-clockwise twists.

You must move your simulation on the grid in FEMM such that it is symmetrical about the absolute point 0,0. I do this as I am building each of my FEMM sims, I also build them about point 0,0.

You must move your simulation on the grid in FEMM such that it is symmetrical about the absolute point 0,0. I do this as I am building each of my FEMM sims, I also build them about point 0,0.

Thanks, I guessed that this was true and have started to move the center of rotation for my models to the absolute 0,0 point on the surface.

But this brings up another question:

What does it mean to select a block and then ask for torque? Are we in effect asking "what torque does THIS block exert on 0,0"? Does it make sense to select all the elements of the model, including the air, and then ask for torque? (as long as they all are physically connected somehow)

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Yes, the positive and negative torque values equate to the clockwise/counter-clockwise twists.

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No, Positive torque equals anticlockwise movement about 0,0.  Negative torque equals clockwise movement about 0,0

Any third opinion?

I was just saying that the positive and negative values of torque tell you which way the pieces are rotating, either clockwise or counter-clockwise depending on the value.

Depends, for instance, I circular magnet (designed as the rotor) centered over 0,0 and selected it to determine how much torque it was feeling. Or, I could pick all the elements around this magnet (which are in effect the stator) and check the torque value and it was exactly opposite that of the magnet at 0,0 (which of course would be the result).

You have to pick the pieces based on knowing what is supposed to rotate or not. You don't need to select the air, because FEMM is taking all the pieces that you don't select into account when you calculate torque for any given piece/pieces.

Thanks tao, that helps. I like the idea of checking results against each other to see if things make sense.

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I was just saying that the positive and negative values of torque tell you which way the pieces are rotating, either clockwise or counter-clockwise depending on the value.

Thanks tao, but acp disagrees and says the opposite, so I am still not sure which it is. I tend to think that a positive value would be clockwise, and a negative value counter-clockwise but that is just my cultural bias in thinking.

I tried constructing examples where I felt I could predict the twist, and compared my expectations with the FEMM result, but then I realized I wasn't sure about 0,0 and other things, so the results confused me.

I never said that positive = clockwise, I was just answering your original question, and acp incorrectly corrected me, even though I never made that statement.

To be clear, if it's needed:

positive torque value = counter-clockwise rotation
negative torque value = clockwise rotation

tao says

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Yes, the positive and negative torque values equate to the clockwise/counter-clockwise twists.

tao also says

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I never said that positive = clockwise, I was just answering your original question, and acp incorrectly corrected me, even though I never made that statement.

To be clear, if it's needed:

positive torque value = counter-clockwise rotation
negative torque value = clockwise rotation

Well, yes, I must be wrong then....   Which one is it then? your first answer or your second? I'm sticking by my answer which, incidently, is the correct one........

Just to be clear, my first answer doesn't say positive=clockwise and negative=counter-clockwise. All my first answer says is that the + and - values given equate to different twisting directions... You then posted the correlations +=anticlockwise and -=clockwise, but said that I had mine wrong, when I made no correlations in my first answer.

I KNEW that positive=counter-clockwise and etc..., but my first 'answer' wasn't correlating that, it was correlating the fact that the + and - values of torque determine the rotation directions...

what a lot of bollocks...

come on, stop waffling, the original poster asked if positive torque values equal clockwise direction and you told him    "Yes, the positive and negative torque values equate to the clockwise/counter-clockwise twists."  Now, if you claim that you weren't being specific, then why bother writing it in the first place when it is only going to confuse the guy? Goodness, is it so hard to admit you were wrong??

By the way, you were correlating in your original reply by dint of the ordering of your sentence, at any rate thats how 99.9% of people would have read it.

I agree in how it looks, I wasn't even going to write that first sentence, lol, seriously!

I wrote the second sentence first about repositioning to point 0,0 and something told me to add that torque values sentence before the repositioning one, which I did, and now look at what it caused hahaha! I have to admit, looking back at his original torque values question and my answer, it would certainly seem that I was correlating positive=clockwise etc as the answer to his question. I seriously didn't mean it that way, so, lets leave it at that, it was a sentence added in haste that has now spawned a nice little discussion, lol!!!

I would admit I was wrong, if I was, I don't lie... The only thing I now see that I was wrong about is in writing that sentence, while not re-reading his original question.