the drive device is provided for inclusion in a windmill with two counter - rotating screws . the shafts of the screws are each connected to a spindle of an epicyclical gearbox , the third spindle providing the energy for the user . the device further comprises a brake device simultaneously acting on the two shafts of the screws . in particular , said device permits the installation of a second screw on a windmill mast designed for a single screw on a windmill mast designed for a single screw , thus greatly increasing the power supplied .