Non-linear Controller for a Drone with Slung Load

This paper presents a control strategy for a quadcopter carrying a slung load. The Euler–Newton method is used for obtaining the complete non-linear model of the 6-DOF quadcopter system and a slung-load system capable of performing the swing motion along two directions. Both the system dynamics are coupled by adding the swing forces to the body forces of the quadcopter. This coupling leads to the undamped swing motion of the slung load which may cause unstable oscillations for the quadcopter, thereby degrading its performance. It is important to damp this undesired swing motion of the slung load. The objective of the controller is to allow the quadcopter to transport a slung load to the desired position without affecting flight stability. A combination of proportional-integral-derivative (PID) and non-linear PID (NLPID) controllers is used for the target position tracking control. A separate PID controller is used for damping the slung load’s oscillations.