A process for assembling a rotor of a variable-reluctance synchronous motor, wherein it comprises steps of: i. preparing a plurality of identical discs, wherein each disc has at least a through-cavity for each polar sector for housing at least a magnet; ii. positioning a plurality of discs in sequence along an axis of rotation for forming the rotor, so that said through-cavities are aligned to one another in a parallel direction to said axis of rotation; iii. preparing a plurality of said magnets with a predefined depth that is identical for at least a part of said magnets and having a section area, according to a plane that is perpendicular to the direction of said axis of rotation, that is equal to or smaller than the section area of said through-cavity, according to a plane that is perpendicular to the direction of said axis of rotation, said predefined depth of each magnet being smaller than the total depth of the rotor; iv. calculating the number of magnets to be inserted, for each polar sector, in a sequence along said direction parallel to said axis of rotation, so as to occupy only part of the total depth of the rotor as a function of predetermined performances of motor torque which are to be obtained, wherein the step of inserting includes said magnets being arranged symmetrically with respect to said axis of rotation in each disc; v. inserting the calculated number of magnets in at least a through-cavity of each polar sector so as to occupy the aligned through-cavities of a plurality of said discs arranged in sequence up to obtaining the depth defined by the calculated number of magnets; vi. realising modules of two types, on the basis of the presence or the absence of the magnets and arranging a variable number of both in sequence for the formation of the rotor; wherein the step of realising modules comprises the following steps of: vii. realizing magnetised modules, wherein each magnetised module comprises a predefined number of said discs and magnets inserted in the cavities of each polar sector, and wherein all the magnetised modules and all the magnets inserted therein have the same predefined depth; viii. realising empty modules without magnets, wherein each empty module comprises a predefined number of said discs without magnets, characterised in that all the empty modules and all the magnetised modules have the same predefined depth, wherein said magnetised modules and said empty modules are mutually interchangeable as a function of the torque performances of the motor that are to be obtained. i. preparing a plurality of identical discs, wherein each disc has at least a through-cavity for each polar sector for housing at least a magnet; ii. positioning a plurality of discs in sequence along an axis of rotation for forming the rotor, so that said through-cavities are aligned to one another in a parallel direction to said axis of rotation; iii. preparing a plurality of said magnets with a predefined depth that is identical for at least a part of said magnets and having a section area, according to a plane that is perpendicular to the direction of said axis of rotation, that is equal to or smaller than the section area of said through-cavity, according to a plane that is perpendicular to the direction of said axis of rotation, said predefined depth of each magnet being smaller than the total depth of the rotor; iv. calculating the number of magnets to be inserted, for each polar sector, in a sequence along said direction parallel to said axis of rotation, so as to occupy only part of the total depth of the rotor as a function of predetermined performances of motor torque which are to be obtained, wherein the step of inserting includes said magnets being arranged symmetrically with respect to said axis of rotation in each disc; v. inserting the calculated number of magnets in at least a through-cavity of each polar sector so as to occupy the aligned through-cavities of a plurality of said discs arranged in sequence up to obtaining the depth defined by the calculated number of magnets; vi. realising modules of two types, on the basis of the presence or the absence of the magnets and arranging a variable number of both in sequence for the formation of the rotor; wherein the step of realising modules comprises the following steps of: vii. realizing magnetised modules, wherein each magnetised module comprises a predefined number of said discs and magnets inserted in the cavities of each polar sector, and wherein all the magnetised modules and all the magnets inserted therein have the same predefined depth; viii. realising empty modules without magnets, wherein each empty module comprises a predefined number of said discs without magnets, characterised in that all the empty modules and all the magnetised modules have the same predefined depth, wherein said magnetised modules and said empty modules are mutually interchangeable as a function of the torque performances of the motor that are to be obtained. vii. realizing magnetised modules, wherein each magnetised module comprises a predefined number of said discs and magnets inserted in the cavities of each polar sector, and wherein all the magnetised modules and all the magnets inserted therein have the same predefined depth; viii. realising empty modules without magnets, wherein each empty module comprises a predefined number of said discs without magnets, characterised in that all the empty modules and all the magnetised modules have the same predefined depth, wherein said magnetised modules and said empty modules are mutually interchangeable as a function of the torque performances of the motor that are to be obtained.