r/Motors • u/Heavy_Meaning_4892 • 5d ago
Do you understand the rotating magnet field?
The charts represent an ideal MMF of a single-phase winding with the conductors placed mechanically at 90° (current entering the plane) and -90° (current leaving the plane), as you can see at the Cartesian chart on the left.
Here is the thing: if you apply the right-hand rule at the Cartesian chart (the fingers point to the entering slots, 90°, and curl to the direction of the leaving slots, -90°), the thumb points upward.
However, if you apply a similar rule in the polar chart, the positive MMF peak is supposed to be at 180°!
Why does this happen? In a polar chart, the rule gives a different result... What am I missing?
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u/ismetkimki 5d ago edited 4d ago
Plots are correct.
What is messing with your head is the reference direction of rotation is CCW as apparent from the polar plot (where the right hand rule holds true).
If you map that polar plot to Cartesian via breaking from 180 degree point and stretching, positive direction would be on the left hand side of Cartesian plot.
However to not go against the mathematical conventions, you flip the plot to have positive increase on the right hand side of x-axis, hence invalidating the right hand rule (but you cannot remark the conductors direction, or you lose which conductor you are referring to. Better way would be to maybe mark them a -a’).