It is in fact clear that the fitting of the rotary motor, or at least a part thereof, such as the rotor winding in this case, directly on the spindle eliminates any mechanical transmission between the latter and the motor itself; in the present instance, with respect to the first example of FIG. 1 it can be observed that the toothed belt 8 and pulleys 9, 10, and also the splined shell 12 are elimi