Hybrid Adaptive Control of an Unbalanced Tilting-rotors Quadcopter Transporting a Payload via an Elastic Cable

Aerial load transportation using quadcopters is a topic of great interest to the robotics community due to its many potential civilian and military applications. This paper presents a nonlinear nine-degree-of-freedom mathematical model for an unbalanced tilting-rotors quadcopter with a suspended load via an elastic cable, where the quadcopter's center of gravity and sling-load suspension point are assumed arbitrarily shifted from the quadcopter's geometric center. The transportation mission is decomposed into six discrete stages, namely Payload Setup, Carrier Alignment, Payload Pick-up, Payload Conveyance, Payload Delivery, and Carrier Landing. Subsequently, a hybrid control technique is proposed, and applied through nonlinear simulations to a case study. The simulation results showed the effectiveness of the proposed controller in achieving satisfactory performance, with acceptable control effort, for the carrier-payload system through a full transportation mission.