The main objective of this thesis project is to design an electromechanical rotative damper for automotive applications: in particular the work is focused on the design of the gear transmission stage and then on the development of the damper actuator assembly to realize a prototype for bench testing. A preliminary analysis of the state of the art of rotative dampers gives some hints on possible solutions concerning the assembly, the gearbox and the leverages. The first design phase is concerning the gearbox: on the base of a previous study, the configuration selected is a double stage planetary gear set. The dimensioning of the planetary stage is performed with KISSsoft software: the target of the optimization is to minimize the size of the gears while keeping acceptable values of safety factors.