A servo-drive of a rotary actuator for controlling an opening cross-section of a medium conducting flow line for internal combustion engines, comprising a diametrically magnetized rotor (14) having a longitudinal axis, said magnetized rotor is for rotation about a longitudinal axis, a stator (3) with two poles (33, 34) and at least one winding for inducing a magnetic field, said stator (3) has a yoke (35) with two legs (38, 39) and a through-opening (13) and is formed by stacking first and second individual sheet-metal laminas (6) alternately, and the rotor (14) is arranged in the through-opening (13), the two poles (33, 34) are constructed on a wall of the through-opening (13) in such a way that one pole (33) is located on a side of the through-opening (13) facing the at least one winding (5) which is located between the legs (38, 39) and one pole (34) which is located on a side of the through-opening (13) facing away from the at least one winding (5), and at least one weak point (40) in the form of a recess (41) is formed in the two poles (33, 34) of said first sheet-metal lamina, and a gap (42) that completely penetrates the two poles (33,34) in a radial direction is formed in a wall of said second sheet metal lamina in each pole (33, 34) in the radial direction, wherein the second group of sheet-metal laminas (6) having gaps (42) as weak points (40) is disposed between said first group of sheet-metal laminas (6) having recesses (41) as weak points (40), and wherein in a multiple repeating way, the second group of sheet-metal laminas (6) with gaps (42) is disposed between the first group of sheet-metal laminas (6) with recesses (41) and are stacked in alternation to form the stator (3).