Orient coils for rot mag field?

Using four phases would be an overkill.

Mount two coils with their axes in the same plane but at a 90 degree angle, and drive them with two sine waves at the same frequency but with a 90 degree phase shift (which is to say with the sine and the cosine wave).

Since you have four coils, putting two each in series allows you to set up a symmetrical arrangement, with an empty space in the middle where you can best exploit your rotating magnetic field, but generating the 180 and 270 degree phase shifted waveforms would be a complete waste of time - you'd get the same effect by routing the 0 degree and 90 degree currents through a second coil in the opposite direction, and anyway you don't actually want to do that.

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-- Bill Sloman, Nijmegen

Look into Helmholtz coils if you want a region of rotating field with good homogeneity; 'discarded' solenoids are likely not optimal.

Ken S. Tucker is a pretentious bullshit artist, whose posts are uniquely uninformative (except about his personality defects).

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would be "radial" coils, while

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would be "circumferential" coils. The latter might give you more open area in the middle to exploit your rotating magnetic field, but a less intense field (since it is off the axes of the coil).

One can only wonder what he thought he meant by "fine tuning" ...

His response is probably going to include a reference to some emiminent physicist (who is now safely dead) and some suggestion that any informative explanation would have to be couched in terms of tensor calculus.

-- Bill Sloman, Nijmegen

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Really? That's not how the professors I associate with do it - they tailor their comments to make them comprehensible to the target audience. But they do have the wit to produce comprehensible comments.

-- Bill Sloman, Nijmegen