Rotational actuating system comprising: - at least one electrical motor (M, 26, 26'), - at least one reducing device comprising two driving drums (2, 4, 2', 4', 102, 104), two sheave wheels (6, 8, 6', 8', 106, 108) each mounted in a yolk (C1, C2), at least one driving cable or a belt (10, 10', 110, 110') travelling from a first driving drum (2, 2', 102) to a sheave wheel (6, 6', 106), from said sheave wheel (6, 6', 106) to the second driving drum (4, 4', 104), from said second driving drum (4, 4', 104) to the other sheave wheel (8, 8', 108) and from said other sheave wheel (8, 8', 108) to the first driving drum (2, 2', 102), a driven cable (12, 12'), one strand of which travels from the yolk of one of the sheave wheels (6, 6', 106) to a driven wheel (14, 14') and one strand travels from the driven wheel (14, 14') to the yolk of the other sheave wheel (8, 8', 108), the driving drums (2, 4, 2', 4', 102, 104) having different diameters and/or different rotation speeds so that the rotation of the driving drums (2, 4, 2', 4', 102, 104) causes a reduction, respectively an increase, in the distance between one of the sheave wheels (6, 8, 6', 8', 106, 108) and the driving drums (2, 4, 2', 4', 102, 104) simultaneously to an increase, respectively reduction, in the distance between the other sheave wheels (8, 6, 8,' 6', 108, 106) and the driving drums (2, 4, 2', 4', 102, 104), driving the driven cable (12, 12') and a rotation movement of the driven wheel (14, 14'), wherein the driving drums (102, 104) have separate rotation axes, and wherein the reducing device comprises two strands of driving cables or two strands of driving belt (110, 110'), one strand of driving cable travelling between the first driving drum, the first sheave wheel and the second driving drum and one strand of driving cable travelling between the first driving drum, the second sheave wheel and the second driving drum, and wherein the motor is in direct drive or via transmission means with one of the driving drums and the transmission means are provided between the first and second driving drums or between the motor and the second driving drum, said system comprising a controller associated with the motor, making it possible to vary and control the synchronisation ratio between the two drums. - at least one electrical motor (M, 26, 26'), - at least one reducing device comprising two driving drums (2, 4, 2', 4', 102, 104), two sheave wheels (6, 8, 6', 8', 106, 108) each mounted in a yolk (C1, C2), at least one driving cable or a belt (10, 10', 110, 110') travelling from a first driving drum (2, 2', 102) to a sheave wheel (6, 6', 106), from said sheave wheel (6, 6', 106) to the second driving drum (4, 4', 104), from said second driving drum (4, 4', 104) to the other sheave wheel (8, 8', 108) and from said other sheave wheel (8, 8', 108) to the first driving drum (2, 2', 102), a driven cable (12, 12'), one strand of which travels from the yolk of one of the sheave wheels (6, 6', 106) to a driven wheel (14, 14') and one strand travels from the driven wheel (14, 14') to the yolk of the other sheave wheel (8, 8', 108), the driving drums (2, 4, 2', 4', 102, 104) having different diameters and/or different rotation speeds so that the rotation of the driving drums (2, 4, 2', 4', 102, 104) causes a reduction, respectively an increase, in the distance between one of the sheave wheels (6, 8, 6', 8', 106, 108) and the driving drums (2, 4, 2', 4', 102, 104) simultaneously to an increase, respectively reduction, in the distance between the other sheave wheels (8, 6, 8,' 6', 108, 106) and the driving drums (2, 4, 2', 4', 102, 104), driving the driven cable (12, 12') and a rotation movement of the driven wheel (14, 14'),