When two polyphase AC windings of differing pole number are housed in a common AC machine stator, their separate MMFs combine additively in some regions of the machine and subtractively in others. The envelope described by the peaks of the total MMF pattern rotates at a speed given by the difference between the supply frequencies to the two windings, divided by the difference in the number of pole pairs. This can form the basis of a reluctance machine with a synchronous speed of 6000 RPM for 50 Hz excitation.The flux pattern consists of two components of short wavelength and small flux per pole, while the pattern of radial force between stator and rotor contains a component of long wavelength. This feautre is the basis for an improved form of low speed rolling rotor machine and for the compliant-core machine in which the rotordeforms to make mechanical contact with the stator.