The rotor is held on a shaft by means of a membrane providing an easy resilient deflection in axial direction and being stiff for torque transmission in azimuthal direction. The membrane is star-shaped, or has spiral arms or is of polygonal configuration. A membrane carrier is connected to a central part of the membrane or to polygon corner points; the rotor, through a sleeve extension of a short circuiting ring is connected to peripheral points of the membrane. The carrier is splined to or slip friction coupled to the shaft.
