Design and Control of a Variable Aerial Cable Towed System

Aerial Cable Towed Systems (ACTS) are composed of several Unmanned Aerial Vehicles (UAVs) connected to a payload by cables. Compared to towing objects from individual aerial vehicles, an ACTS has significant advantages such as heavier payload capacity, modularity, and full control of the payload pose. \added{They are however generally large with limited ability to meet geometric constraints while avoiding collisions between UAVs.} This paper presents \added{the modelling, performance analysis, design, and a proposed controller for} a novel ACTS with variable cable lengths, named Variable Aerial Cable Towed System (VACTS). Winches are embedded on the UAVs for actuating the cable lengths similar to a Cable-Driven Parallel Robot to increase the versatility of the ACTS. The general geometric, kinematic and dynamic models of the VACTS are derived, followed by the development of a centralized feedback linearization controller. The design is based on a wrench analysis of the VACTS, without \added{constraining the cables to pass through the UAV center of mass, as in current works}. Additionally, the performance of the VACTS and ACTS are compared \added{showing that the added versatility comes at the cost of payload and configuration flexibility}. A prototype confirms the feasibility of the system.