Recent applications of unmanned aerial systems (UAS) to precision agriculture have shown increased ease and efficiency in data collection at precise remote locations. However, further enhancement of the field requires operation over long periods of time, e.g. days or weeks. This has so far been impractical due to the limited flight times of such platforms and the requirement of humans in the loop for operation. To overcome these limitations, we propose a fully autonomous rotorcraft UAS that is capable of performing repeated flights for long-term observation missions without any human intervention. We address two key technologies that are critical for such a system: full platform autonomy to enable mission execution independently from human operators and the ability of vision-based precision landing on a recharging station for automated energy replenishment. High-level autonomous decision making is implemented as a hierarchy of master and slave state machines. Vision-based precision landing is enabled by estimating the landing pad's pose using a bundle of AprilTag fiducials configured for detection from a wide range of altitudes. We provide an extensive evaluation of the landing pad pose estimation accuracy as a function of the bundle's geometry. The functionality of the complete system is demonstrated through two indoor experiments with a duration of 11 and 10.6 hours, and one outdoor experiment with a duration of 4 hours. The UAS executed 16, 48 and 22 flights respectively during these experiments. In the outdoor experiment, the ratio between flying to collect data and charging was 1 to 10, which is similar to past work in this domain. All flights were fully autonomous with no human in the loop. To our best knowledge this is the first research publication about the long-term outdoor operation of a quadrotor system with no human interaction.
Several rotorcraft UAS that are capable of autonomous, long-duration mission execution in benign indoor (VICON) environments have previously appeared in literature. Focusing on the recharging solution to extend individual platform flight time and a multi-agent scheme for constant operation, impressive operation times have been demonstrated ( @cite_28 : 24 h single vehicle experiment; @cite_5 : 9.5 h with multiple vehicles). Recharging methods vary from wireless charging @cite_56 to contact-based charging pads @cite_5 to battery swap systems @cite_27 @cite_38 . While wireless charging offers the most flexibility since no physical contact has to be made, charging currents are low resulting in excessively long charging times and are hence not an option for quick redeployment. However, interesting results have been shown in @cite_56 demonstrating wireless powering of a 35 g 10 W micro drone in hover flight. On the other end of the spectrum, battery swap systems offer immediate redeployment of a UAS, but require sophisticated mechanisms to be able to hot swap a battery, and a pool of charged batteries that are readily available. This makes such systems less attractive for maintenance free and cost effective long-term operation.
@cite_38 @cite_28 @cite_56 @cite_27 @cite_5
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Future Unmanned Aircraft Systems (UASs) are expected to be nearly autonomous and composed of heterogeneous Unmanned Aerial Vehicles (UAVs). While most of the current research focuses on UAV avionics and control algorithms, ground task automation has come to the attention of researchers during the past few years. Ground task automation not only relieves human operators, but may also expand the UAS operation area, improve system coverage and enable operation in risky environments without posing a threat to humans. We propose a model to evaluate the coverage of a given UAS. We also compare different solutions for various modules of an automated battery replacement system for UAVs. In addition, we propose a ground station capable of swapping a UAV's batteries, followed by a discussion of prototype components and tests of some of the prototype modules. The proposed platform is well-suited for high-coverage requirements and is capable of handling a heterogeneous UAV fleet. This paper presents the development and implementation of techniques used to manage autonomous unmanned aerial vehicles (UAVs) performing 24 7 persistent surveillance operations. Using an indoor flight testbed, flight test results are provided to demonstrate the complex issues encountered by operators and mission managers when executing an extended persistent surveillance operation in realtime. This paper presents mission health monitors aimed at identifying and improving mission system performance to avoid down time, increase mission system eciency and reduce operator loading. This paper discusses the infrastructure needed to execute an autonomous persistent surveillance operation and presents flight test results from one of our recent automated UAV recharging experiments. Using the RAVEN at MIT, we present flight test results from a 24 hr, fully-autonomous air vehicle flight-recharge test and an autonomous, multi-vehicle extended mission test using small, electric-powered air vehicles. Recent developments in high frequency inductive wireless power transfer (WPT) mean that the technology has reached a point where powering small autonomous drones has become feasible. Fundamentally, drones can only carry very limited payloads and thus require light-weight WPT receiver solutions. The key to achieving light weight is operating the WPT system at high frequency: this allows both the coils and the electronics to achieve very high gravametric power densities. When operated in the MHz region, the WPT coils can be manufactured without the need for ferrite, because the low coupling factor can be offset by very high coil Q factors. To make efficient MHz power conversion circuits, wide band-gap semiconductors, including Silicon Carbide (SiC) and Gallium Nitride (GaN) have provided a step change. For powering a drone, these devices are integrated into soft-switching resonant inverter and rectifier topologies and are able to operate efficiently at tens of MHz and hundreds of watts. In addition, recently discovered designs that make these inverters tolerant to load variations and have inherent voltage or current regulation features enable an WPT system to operate effectively as the separation distance and alignment between transmitter and receiver changes, which is critical when charging a flying drone. It will be shown that combining all these individual developments has enabled the charging of a 10 W micro-drone whilst hovering in the vicinity of a charging pad. The past decade has seen an increased interest towards research involving Autonomous Micro Aerial Vehicles (MAVs). The predominant reason for this is their agility and ability to perform tasks too difficult or dangerous for their human counterparts and to navigate into places where ground robots cannot reach. Among MAVs, rotary wing aircraft such as quadrotors have the ability to operate in confined spaces, hover at a given point in space and perch1 or land on a flat surface. This makes the quadrotor a very attractive aerial platform giving rise to a myriad of research opportunities. The potential of these aerial platforms is severely limited by the constraints on the flight time due to limited battery capacity. This in turn arises from limits on the payload of these rotorcraft. By automating the battery recharging process, creating autonomous MAVs that can recharge their on-board batteries without any human intervention and by employing a team of such agents, the overall mission time can be greatly increased. This paper describes the development, testing, and implementation of a system of autonomous charging stations for a team of Micro Aerial Vehicles. This system was used to perform fully autonomous long-term multi-agent aerial surveillance experiments with persistent station keeping. The scalability of the algorithm used in the experiments described in this paper was also tested by simulating a persistence surveillance scenario for 10 MAVs and charging stations. Finally, this system was successfully implemented to perform a 9½ hour multi-agent persistent flight test. Preliminary implementation of this charging system in experiments involving construction of cubic structures with quadrotors showed a three-fold increase in effective mission time.