Abstract: An electric device for driving a rotatable mass having a high inertia, said device comprising an electric motor supplied with power by a low-voltage dc source through an electronic energy converter supplying power to the armature (11) of the motor; the field system of the motor (12) comprises magnets (14) and excitation coils (16), the electric conductor of a coil being wound around its pole piece (18) along surfaces parallel to the corresponding yoke portion (19); this device further comprises an electronic system for regulating the current in the coils (16) and capable of maintaining during accelerations and decelerations a maximum output voltage of the converter within a wide range of speeds and therefore a maximum power; the increase in the intensity of the current in the coils (16) progressively decreases the torque coefficient of the motor which is maximum when the coils (16) are not supplied with power.