Power tether for long duration multi-copter flight

The possibilities and promises of unmanned aerial vehicles (UAVs) for smart agriculture, 5G cellular integration, package delivery, and persistent surveillance are but a few of the active drivers for advancing UAV technology and systems. The UAVs' dependence on battery power represents a key limitation for practical deployment. As every remote pilot understands, even a modest research payload can limit a UAV's endurance to under 20 min. When horizontal maneuverability is not required, a power tether from the ground can provide near infinite flight time. Commercial tethers exist but can be prohibitively expensive or underpowered for research payloads. This paper describes the detailed design, construction, and operation of a relatively inexpensive open-source alternative. The designed and prototyped tether system delivers 1 kW of power at the tether base which, on an efficient UAV, corresponds to a payload of approximately 4.75 kg. We discuss the tradeoffs, design choices, best practices, and customization options, and provide empirical data for characterizing the power-payload relationship. The power and payload are scalable thanks to the modular design and the tools presented in this paper. The very low cost compared to commercial heavy-lift tether systems and the open-source design enable reproducibility and widespread use for supporting research, development, and emerging services/applications.