Reduction gear system comprising: - a body having a longitudinal axis 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, 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 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, 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,