This actuator comprises a frame, a motor, an output shaft, and a drive train for driving the output shaft via the motor. The drive train comprises an upstream element, a downstream element, and a device for coupling the upstream element to the downstream element. Said coupling device has a first configuration for transmitting all of the torque exerted by one of the upstream and downstream elements on the coupling device to the other of the upstream and downstream elements when said torque is below a threshold torque, and a second configuration for diverting at least part of said torque exerted by one of the upstream and downstream elements on the coupling device to the frame when said torque is at least equal to the threshold torque.