Sampling-based Motion Planning for Active Multirotor System Identification

This paper reports on an algorithm for planning trajectories that allow a multirotor micro aerial vehicle (MAV) to quickly identify a set of unknown parameters. In many problems like self calibration or model parameter identification some states are only observable under a specific motion. These motions are often hard to find, especially for inexperienced users. Therefore, we consider system model identification in an active setting, where the vehicle autonomously decides what actions to take in order to quickly identify the model. Our algorithm approximates the belief dynamics of the system around a candidate trajectory using an extended Kalman filter (EKF). It uses sampling-based motion planning to explore the space of possible beliefs and find a maximally informative trajectory within a user-defined budget. We validate our method in simulation and on a real system showing the feasibility and repeatability of the proposed approach. Our planner creates trajectories which reduce model parameter convergence time and uncertainty by a factor of four.Comment: Published at ICRA 2017. Video available at https://www.youtube.com/watch?v=xtqrWbgep5

Analysis and Control of a Variable-Pitch Quadrotor for Agile Flight

Fixed-pitch quadrotors are popular research and hobby platforms largely due to their mechanical simplicity relative to other hovering aircraft. This simplicity, however, places fundamental limits on the achievable actuator bandwidth and the possible flight maneuvers. This paper shows that many of these limitations can be overcome by utilizing variable-pitch propellers on a quadrotor. A detailed analysis of the potential benefits of variable-pitch propellers over fixed-pitch propellers for a quadrotor is presented. This analysis is supported with experimental testing to show that variable-pitch propellers, in addition to allowing for generation of reverse thrust, substantially increase the maximum rate of thrust change. A nonlinear, quaternion-based control algorithm for controlling the quadrotor is also presented with an accompanying trajectory generation method that finds polynomial minimum-time paths based on actuator saturation levels. The control law and trajectory generation algorithms are implemented on a custom variable-pitch quadrotor. Several flight tests are shown, which highlight the benefits of a variable-pitch quadrotor over a standard fixed-pitch quadrotor for performing aggressive and aerobatic maneuvers.National Science Foundation (U.S.) (0645960

Rotorcraft Blade Pitch Control Through Torque Modulation

Micro air vehicle (MAV) technology has broken with simple mimicry of manned aircraft in order to fulfill emerging roles which demand low-cost reliability in the hands of novice users, safe operation in confined spaces, contact and manipulation of the environment, or merging vertical flight and forward flight capabilities. These specialized needs have motivated a surge of new specialized aircraft, but the majority of these design variations remain constrained by the same fundamental technologies underpinning their thrust and control. This dissertation solves the problem of simultaneously governing MAV thrust, roll, and pitch using only a single rotor and single motor. Such an actuator enables new cheap, robust, and light weight aircraft by eliminating the need for the complex ancillary controls of a conventional helicopter swashplate or the distributed propeller array of a quadrotor. An analytic model explains how cyclic blade pitch variations in a special passively articulated rotor may be obtained by modulating the main drive motor torque in phase with the rotor rotation. Experiments with rotors from 10 cm to 100 cm in diameter confirm the predicted blade lag, pitch, and flap motions. We show the operating principle scales similarly as traditional helicopter rotor technologies, but is subject to additional new dynamics and technology considerations. Using this new rotor, experimental aircraft from 29 g to 870 g demonstrate conventional flight capabilities without requiring more than two motors for actuation. In addition, we emulate the unusual capabilities of a fully actuated MAV over six degrees of freedom using only the thrust vectoring qualities of two teetering rotors. Such independent control over forces and moments has been previously obtained by holonomic or omnidirection multirotors with at least six motors, but we now demonstrate similar abilities using only two. Expressive control from a single actuator enables new categories of MAV, illustrated by experiments with a single actuator aircraft with spatial control and a vertical takeoff and landing airplane whose flight authority is derived entirely from two rotors

Nonlinear Model Predictive Control for Multi-Micro Aerial Vehicle Robust Collision Avoidance

Multiple multirotor Micro Aerial Vehicles sharing the same airspace require a reliable and robust collision avoidance technique. In this paper we address the problem of multi-MAV reactive collision avoidance. A model-based controller is employed to achieve simultaneously reference trajectory tracking and collision avoidance. Moreover, we also account for the uncertainty of the state estimator and the other agents position and velocity uncertainties to achieve a higher degree of robustness. The proposed approach is decentralized, does not require collision-free reference trajectory and accounts for the full MAV dynamics. We validated our approach in simulation and experimentally.Comment: Video available on: https://www.youtube.com/watch?v=Ot76i9p2ZZo&t=40

Arrival management for eVTOL aircraft in on-demand urban air mobility

The electric vertical takeoff and landing (eVTOL) aircraft can alleviate transportation congestion on the ground by utilizing three-dimensional airspace efficiently. However, the endurance (specific energy) of Lithium-ion Polymer (Li-Po) batteries imposes severe constraints on the operational time-span of an eVTOL on urban air mobility (UAM) passenger transportation mission. The first part of the research focuses on the generation of energy efficient trajectories for eVTOLs with the assigned required times of arrival (RTA)s. The problem formulations are performed in multiphase optimal control framework with energy as the performance index for the following eVTOL aircraft types: (i) multirotor and (ii) tandem tilt-wing. These two types of eVTOLs are chosen because of their performance characteristics falling at the two extremes of the performance spectrum of eVTOLs. The proposed multiphase optimal control problem formulations and the corresponding numerical solutions enable an eVTOL to meet the assigned RTA and achieve the most energy efficient arrival trajectory, which is a critical enabler for the safe and efficient future eVTOL operations for passenger transportation and cargo delivery in UAM environment. The problem formulations are applied to a UAM passenger transport use cases with (i) EHang 184, (ii) Airbus Vahana, and (iii) the Uber Elevate proposed vertiport concept in numerical simulations. The second part of the research involves arrival sequencing and scheduling problem formulation in UAM context for a mixed fleet (winged/wingless) of eVTOLs expected to land on a vertiport. Based on anticipated UAM traffic density in emergent (low) and early expanded (moderate/high) operations, two separate vertiport arrival procedures have been proposed for the problem. The arrival procedure for early expanded operations is proposed based on arrival procedure of emergent operations as a baseline with the addition of metering gate(s) on the boundary of the terminal area (a circular area of radius 400 m around a vertiport) and multiple landing pads on the vertiport. The objective of the problem is to minimize the makespan (landing completion time) of a given set of eVTOLs, which is equivalent to maximizing the vertiport arrival throughput. A heuristic approach called insertion, and local search (ILS) [\cite{Waqar}] combined with two different scheduling methods: i) mixed-integer linear programming (MILP) and ii) time-advance (TA) are proposed to optimize the landing order (sequence) and makespan of the mixed fleet of eVTOLs. Next, the impact of the number of landing pads (N) on the vertiport arrival throughput is studied to aid in early expanded UAM operations (moderate/high traffic density). Finally, sensitivity analysis is performed to see the impact of the following on the sequencing and scheduling algorithms: i) the number of eVTOLs expected to land (n) and ii) the number of eVTOLs used in the local neighborhood search (k). Through numerical simulations and sensitivity analysis, our algorithms demonstrated real-time scheduling capabilities for on-demand UAM arrival operations, which can be used as a potential future service for UAM vertiports and terminal airspace

Development of an Indoor Multirotor Testbed for Experimentation on Autonomous Guidance Strategies

Despite the vast popularity of rotary wing unmanned aerial vehicles and research centres that develop their guidance software, there are only a limited number of references that provide an exhaustive description of a step-by-step procedure to build-up a multirotor testbed. In response to such need, the first part of this thesis aims to describe, in detail, the complete procedure to establish and operate an autonomous multirotor unmanned aerial vehicle indoor experimental platform to test and validate guidance, navigation and control strategies. Both hardware and software aspects of the testbed are described to offer a complete understanding of the different aspects. The second part of this thesis focuses on two benchmarks multirotor guidance, navigation and control problems. Initially, the guidance law for an accurate landing manoeuvre is studied. Multirotor usually have a flight time limited to a few minutes. Autonomous landing and docking to a charging station could extend the mission duration of these vehicles. Subsequently, the guidance strategy for the formation flight between two multirotors is considered. In this case, the fundamental goal is an accurate autonomous alignment between two vehicles, each of them behaving as a target and chaser simultaneously. In the last part of this thesis, the problem of minimum energy manoeuvres is tackled. Again, in this case, the motive is to address the limitation in multirotor flight duration. The fundamental objective of this guidance, navigation and control strategy is to determine and implement, in real-time, the minimum energy control histories that transfer the multirotor from its initial point to a given final point. As opposed to conventional guidance strategies, mostly based on proportional-integral-derivative laws, a minimum energy controller allows the vehicle to execute the manoeuvre with a minimum electrical power expenditure

Development of a flight control architecture for rotary wing UAVs with model based design approach

This thesis describes the design and implementation of various autopilot software architectures for mini/micro rotary-wing unmanned aerial vehicles by exploiting the modelbased design approach. Nowadays in fact, the tendency for software development is changing from manual coding to automatic code generation, in other words, it is becoming model-based. In general, models can be described as abstractions of systems, they are created to serve particular purposes, for example, to present a user-understandable description of the system or to present information in a more intuitive form. Model-based techniques for software design enables the engineer to reduce drastically development time required for software corrections or modi�cations. Under the various chapters, di�erent flight control techniques are presented with theoretical background and tested via simulations and experimental campaigns. All the navigation and control problems presented below arise in development of embedded software that exploits the innovative model-based design technology. In order to provide validations of the proposed solutions, software for simulation and implementation is specialized for the case of multirotor vehicles, which are becoming very helpful systems for many and varied civil operations. This is the reason why part of the text is devoted to multirotor vehicle dynamics

Safe local aerial manipulation for the installation of devices on power lines: Aerial-core first year results and designs

Article number 6220The power grid is an essential infrastructure in any country, comprising thousands of kilometers of power lines that require periodic inspection and maintenance, carried out nowadays by human operators in risky conditions. To increase safety and reduce time and cost with respect to conventional solutions involving manned helicopters and heavy vehicles, the AERIAL-CORE project proposes the development of aerial robots capable of performing aerial manipulation operations to assist human operators in power lines inspection and maintenance, allowing the installation of devices, such as bird flight diverters or electrical spacers, and the fast delivery and retrieval of tools. This manuscript describes the goals and functionalities to be developed for safe local aerial manipulation, presenting the preliminary designs and experimental results obtained in the first year of the project.European Union (UE). H2020 871479Ministerio de Ciencia, Innovación y Universidades de España FPI 201