motor radial magnetic pull

[electricpete]

In the presence of a static eccentricity, there will be a pull on the rotor away from the center. I understand there is a "dc" (constant) component and a 120hz component. (similar to what you get when you evaluate cos^2).

Does anyone have a formula for those two force components as a function of eccentricity and number of poles?

In particular, I'm trying to understand why some people say that the pull on the rotor for given eccentricity is larger for 2-pole motor. (I'm not talking about vibration... which is larger for 2-pole due to the more flexible mode-shape of 2-pole stator deformation.... but about the force or pull on the rotor).

(From my perspective, I would have thought that the force on a 2-pole motor would be less based on the flux pattern which flows approx 180 degrees through rotor.)

Any thoughts?

 

[jbartos]

Suggestion: Visit

http://www.jsme.or.jp/English/emnews02.html

(for (2) Large Output and Low Noise Motor for Electrical Power Steering)
and Reference:
1. A.E. Fitzgerald, Charles Kingsley, Jr., Stephen D. Umans, Electric Machinery, 5th Ed., McGraw-Hill, Inc., 1990
3-1 Forces and Torques in Magnetic Field Systems, page 98
2.

http://www.fb3.fh-dortmund.de/personen/aschendo/publikationen/unsymo/unsymo.htm