Comparing Magnetic Bearings with Symmetry of 3

The stators of Active Magnetic Bearings (AMBs) usually show a symmetry of 4, because the magnetic forces applied to the rotor are generated in 4 points in a plane, two in the canonical x direction and two in the y direction. AMBs with symmetry of 3 are harder to find, either in real-world applications or in the specific literature. Their stators generate forces in 3 coplanar points; one of these points, at most, can lie in one of the canonical x,y directions. In this paper, basic aspects of the symmetry of 3 will be explained; they will help to develop the mathematical models of symmetry of 3 AMBs and to compare some situations in this world with the corresponding facts in the symmetry of 4 devices.