Motorization device comprising: • two substantially parallel winding cylinders (1a, 1b), longitudinal link element-forming winding means, the winding means being capable of maintaining a predetermined distance between the two winding cylinders (1a, 1b) and being wound around the two winding cylinders (1a, 1b), the winding means consequently having a crossover point between two substantially linear sections (3a, 3b) of the link element situated between the winding cylinders (1a, 1b), • at least two flexible tracks (2a, 2b), an assembly comprising a winding cylinder among both winding cylinders (1a, 1b) and a flexible track (2a, 2b) forming a fitting (12a, 12b), a flexible track among the at least two flexible tracks (2a, 2b) being fixed to each winding cylinder (1a, 1b), the flexible tracks (2a, 2b) being arranged facing one another and having a point of contact, a prestressing force being applied at said point of contact of the flexible tracks (2a, 2b) under the effect of the winding means, the flexible tracks (2a, 2b) having a spiral form, the form of the spiral being configured in such a way that the point of contact between the two flexible tracks (2a,2b) is eccentric relative to the crossover point of the winding means, the point of contact and the crossover point not being aligned on one and the same axis parallel to the axes of revolution of the winding cylinders (1a, 1b), so that a torque dependent on the distance between the point of contact and the crossover point is applied, the torque being able to provoke the mutual rotation of the fittings (12a, 12b), the motorization device being characterized in that each winding cylinder (1a, 1b) has a first circumference over a determined first portion (11a, 11b), and a second circumference over a determined second portion (13a, 13b), the first circonference of each winding cylinder being different from the second circonference of each winding cylinder, each linear section (3a, 3b) of the link element winding on the first portion of the first winding cylinder and on the second portion of the second winding cylinder, or on the second portion of the first winding cylinder and on the first portion of the second winding cylinder. • two substantially parallel winding cylinders (1a, 1b), longitudinal link element-forming winding means, the winding means being capable of maintaining a predetermined distance between the two winding cylinders (1a, 1b) and being wound around the two winding cylinders (1a, 1b), the winding means consequently having a crossover point between two substantially linear sections (3a, 3b) of the link element situated between the winding cylinders (1a, 1b), • at least two flexible tracks (2a, 2b), an assembly comprising a winding cylinder among both winding cylinders (1a, 1b) and a flexible track (2a, 2b) forming a fitting (12a, 12b), a flexible track among the at least two flexible tracks (2a, 2b) being fixed to each winding cylinder (1a, 1b), the flexible tracks (2a, 2b) being arranged facing one another and having a point of contact, a prestressing force being applied at said point of contact of the flexible tracks (2a, 2b) under the effect of the winding means, the flexible tracks (2a, 2b) having a spiral form, the form of the spiral being configured in such a way that the point of contact between the two flexible tracks (2a,2b) is eccentric relative to the crossover point of the winding means, the point of contact and the crossover point not being aligned on one and the same axis parallel to the axes of revolution of the winding cylinders (1a, 1b), so that a torque dependent on the distance between the point of contact and the crossover point is applied, the torque being able to provoke the mutual rotation of the fittings (12a, 12b),