Reduction gear system comprising: - a body having a longitudinal axis (X) with, at a first end, a coupler intended to be connected to a motor shaft of a motor , and, at a second end, an output shaft , in which the coupler and the output shaft are mounted to be movable in rotation with respect to the body about the longitudinal axis (X), in which the body comprises a drum with an inner face, - a first epicyclic gear train comprising an input planet gear integral to the coupler , a first planet gear carrier in the form of a first circular plate on which a plurality of first planet gears are mounted to be movable in rotation, in which each meshes with the input planet gear , and first teeth which mesh with the first planet gears and which are disposed on the inner face of the drum which constitutes a planet gear crown ring, - a second epicyclic gear train comprising an intermediate planet gear integral to the first planet gear carrier , a second planet gear carrier in the form of a second circular plate on which a plurality of second planet gears are mounted to be movable in rotation, in which each meshes with the intermediate planet gear , and second teeth which mesh with the second planet gears and which are disposed on the inner face of the drum which constitutes a planet gear crown ring, and - a third epicyclic gear train comprising an output planet gear integral to the second planet gear carrier , a third planet gear carrier on which a plurality of third planet gears are mounted to be movable in rotation, in which each meshes with the output planet gear , and third teeth which mesh with the third planet gears and which are disposed on the inner face of the drum which constitutes a planet gear crown ring, in which the output shaft is integral to the third planet gear carrier , the reduction gear system being characterized in that it comprises a first toothed ring having a central hole in which is fitted the first circular plate , comprising, on the outer periphery of the first toothed ring , teeth which cooperate with the second teeth . - a body having a longitudinal axis (X) with, at a first end, a coupler intended to be connected to a motor shaft of a motor , and, at a second end, an output shaft , in which the coupler and the output shaft are mounted to be movable in rotation with respect to the body about the longitudinal axis (X), in which the body comprises a drum with an inner face, - a first epicyclic gear train comprising an input planet gear integral to the coupler , a first planet gear carrier in the form of a first circular plate on which a plurality of first planet gears are mounted to be movable in rotation, in which each meshes with the input planet gear , and first teeth which mesh with the first planet gears and which are disposed on the inner face of the drum which constitutes a planet gear crown ring, - a second epicyclic gear train comprising an intermediate planet gear integral to the first planet gear carrier , a second planet gear carrier in the form of a second circular plate on which a plurality of second planet gears are mounted to be movable in rotation, in which each meshes with the intermediate planet gear , and second teeth which mesh with the second planet gears and which are disposed on the inner face of the drum which constitutes a planet gear crown ring, and - a third epicyclic gear train comprising an output planet gear integral to the second planet gear carrier , a third planet gear carrier on which a plurality of third planet gears are mounted to be movable in rotation, in which each meshes with the output planet gear , and third teeth which mesh with the third planet gears and which are disposed on the inner face of the drum which constitutes a planet gear crown ring, in which the output shaft is integral to the third planet gear carrier , <EOS>