Design and modeling of a modular payload carrying tethered drone system

Abstract

Unmanned Aerial Vehicles (UAVs) are currently employed in a plethora of applications, spanning both military and civilian sectors. A key limitation of conventional UAVs is their restricted flight time and operational range. Efforts to extend this range often come at the expense of reduced payload capacity. Tethered drones offer a promising solution to overcome these limitations, where power and communication are transmitted through a tether, allowing the system to achieve substantially longer flight times compared to conventional drones.

This thesis defines the capabilities and limitations of a tethered drone designed for high-capacity and modular payload applications. The system is constrained by predefined dimensions for the drone, ground base, and the upper and lower payload. The system is separated into different subsystems, each of which is investigated individually based on a series of research questions. Design decisions are based on the predefined constraints, along with additional requirements derived from a range of potential applications. Furthermore, a concept generation and evaluation phase is conducted, during which concepts are iteratively assessed through performancebased comparisons. A hexacopter with three-bladed foldable propellers, capable of landing in any yaw-angle, emerges as the most suitable solution. This concept offers additional margins in thrust compared to other viable solutions. This additional thrust can be allocated to increase acceleration, extend tether length, enhance payload capacity, or prolong untethered flight duration.

Following this, the hexacopter and tether are modeled using the Euler Lagrange method, with the tether modeled as a lumped mass model. The modeling, based on a comprehensive literature review, identifies the appropriate governing system equations and results in a coupled system of ADEs. The system is subsequently controlled using cascaded PID control and simulated in Simulink to validate the system design and to assess its performance in terms of stability, robustness and redundancy. Key performance metrics, including recommended tether tension, optimal payload distribution, and maximum operating time are also computed by means of simulation under various environmental conditions and payload variations.