Capable of supporting large radial loads due to heavy panels, with a simplified assembly but without compromise in terms of precision and robustness. It comprises an annular structural casing (1), a toothed crown (2) mounted in the structural casing (1), whereon an endless screw (3) actuated by a motor (4) tangentially meshes, the toothed crown (2) of which comprises a central annular protuberance (5) with a toothing that meshes with the endless screw (3), and the circular projections (6) of which of the body of the toothed crown (2) comprise a plurality of threaded holes (7) for connecting the horizontal shafts that support the solar panels for their zenithal orientation, where the toothed crown (2) comprises a toothed track whereon the endless screw (3) tangentially meshes, and two independent raceways.