A motor or electromagnetic generator with a rotor (3) and at least one stator (1, 2), the rotor (3) having permanent magnets (12) rotating around a median shaft and the stator (1, 2) having windings (5). The rotor (3) comprises magnet structures forming magnet poles composed of a plurality of unit magnets (15), covering discs (17) being axially arranged on each of two opposite axial faces of the rotor (3), the covering discs (17) being made of a composite material, the covering discs (17) and the magnet structures (12) being coated in an outer coating layer of composite material defining the outer contour of said at least one rotor (3). The stator (1, 2) comprises concentric windings (5) comprising a series of blocks (4) with the windings (5) wound around each block (4), the blocks (4) being rigidly attached to each other.