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This paper addresses the ongoing process of development of a small hand-held multiple unmanned aerial vehicle platform for surveillance and monitoring. The project cover all phases of development, from aerodynamic design and mechanical assembly, through fine tuning low level control loops and design of an attitude and heading reference system, up to implementation of navigation algorithms and finally flight testing. Commercial hardware is used to speed up development, allowing the team responsible for implementing the navigation algorithms to execute and test while the team responsible for the aerodynamics and electronics can design and compare results. I. INTRODUCTIONSmall Unnamed Aerial Vehicles (SUAVs) are a class of robotic airships, which equipped with cameras and special sensors, can be used in several applications. The importance of these vehicles has grown continuously in the last years, especially for military and reconnaissance purposes, particularly in operations where the tasks are dangerous or tedious for human pilots. A special type of SUAV is constituted by hand launched fixed-wing air vehicles that can be easily operated by a single user in an outdoor environment. For this vehicles, several applications exist, such as forest fire monitoring [1], multispectral agricultural remote sensing and crop management [2], urban environment monitoring [3], real time mapping of disaster areas [4], power line inspection [5] and many others.

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This paper presents a state-of-the-art tethered unmanned aerial vehicle (TUAV) for structural integrity assessment of underground stone mine pillars. The TUAV, powered by its tether, works in tandem with an unmanned ground vehicle (UGV) that hosts the TUAV batteries, a self-leveled landing platform, and the tether management system. The UGV and the TUAV were named Rhino and Oxpecker, respectively, given that the TUAV stays landed on the UGV while the ensemble moves inside a mine. The mission of Oxpecker is to create, using a LiDAR sensor, 3D maps of the mine pillars to support time-lapse hazard mapping and time-dependent pillar degradation analysis. Given the height of the pillars ( 7 – 12m), this task cannot be executed by Rhino alone. This paper describes the drone’s hardware and software. The hardware includes the tether management system, designed to control the tension of the tether, and the tether perception system, which provides information that can be used for localization and landing in global navigation satellite systems (GNSS)-denied environments. The vehicle’s software is based on a state machine that controls the several phases of a mission (i.e., takeoff, inspection, and landing) by coordinating drone motion with the tethering system. The paper also describes and evaluates our approach for tether-based landing and autonomous 3D mapping of pillars. We show experiments that illustrate and validate our system in laboratories and underground mines.