The recent advances in state estimation, perception, and navigation algorithms have significantly contributed to the ubiquitous use of quadrotors for inspection, mapping, and aerial imaging. To further increase the versatility of quadrotors, recent works investigated the use of an adaptive morphology, which consists of modifying the shape of the vehicle during flight to suit a specific task or environment. However, these works either increase the complexity of the platform or decrease its controllability. In this letter, we propose a novel, simpler, yet effective morphing design for quadrotors consisting of a frame with four independently rotating arms that fold around the main frame. To guarantee stable flight at all times, we exploit an optimal control strategy that adapts on the fly to the drone morphology. We demonstrate the versatility of the proposed adaptive morphology in different tasks, such as negotiation of narrow gaps, close inspection of vertical surfaces, and object grasping and transportation. The experiments are performed on an actual, fully autonomous quadrotor relying solely on onboard visual-inertial sensors and compute. No external motion tracking systems and computers are used. This is the first work showing stable flight without requiring any symmetry of the morphology.

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The Foldable Drone: A Morphing Quadrotor That Can Squeeze and Fly

Unmanned Aerial Vehicles (UAVs) are becoming increasingly popular for applications such as inspections, delivery, agriculture, surveillance, and many more. It is estimated that, by 2040, UAVs/drones will become a mainstream delivery channel to satisfy the growing demand for parcel delivery. Though the UAVs are gaining interest in civil applications, the future of UAV charging is facing a set of vital concerns and open research challenges. Considering the case of parcel delivery, handling countless drones and their charging will become complex and laborious. The need for non-contact based multi-device charging techniques will be crucial in saving time and human resources. To efficiently address this issue, Wireless Power Transmission (WPT) for UAVs is a promising technology for multi-drone charging and autonomous handling of multiple devices. In the literature of the past five years, limited surveys were conducted for wireless UAV charging. Moreover, vital problems such as coil weight constraints, comparison between existing charging techniques, shielding methods and many other key issues are not addressed. This motivates the author in conducting this review for addressing the crucial aspects of wireless UAV charging. Furthermore, this review provides a comprehensive comparative study on wireless charging’s technical aspects conducted by prominent research laboratories, universities, and industries. The paper also discusses UAVs’ history, UAVs structure, categories of UAVs, mathematical formulation of coil and WPT standards for safer operation.

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A Review on UAV Wireless Charging: Fundamentals, Applications, Charging Techniques and Standards

This article analyzes the evolution and current trends in aerial robotic manipulation, comprising helicopters, conventional underactuated multirotors, and multidirectional thrust platforms equipped with a wide variety of robotic manipulators capable of physically interacting with the environment. It also covers cooperative aerial manipulation and interconnected actuated multibody designs. The review is completed with developments in teleoperation, perception, and planning. Finally, a new generation of aerial robotic manipulators is presented with our vision of the future. 

Past, Present, and Future of Aerial Robotic Manipulators

In the last decade, the aerial robotics community has witnessed an increased interest in fully actuated multirotor unmanned aerial vehicles (UAVs) that have more capabilities than conventional underactuated multirotors. This article collects the different UAV designs having fully actuated aerodynamic wrench generation proposed in the literature to date. The work includes a systematic derivation of the control-allocation matrix for all of the concepts as well as a discussion of the different quantitative criteria used for optimizing UAV designs.

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Fully Actuated Multirotor UAVs: A Literature Review

This paper presents an omnidirectional aerial manipulation platform for robust and responsive interaction with unstructured environments, toward the goal of contact-based inspection. The fully actuated tilt-rotor aerial system is equipped with a rigidly mounted end-effector, and is able to exert a 6 degree of freedom force and torque, decoupling the system's translational and rotational dynamics, and enabling precise interaction with the environment while maintaining stability. An impedance controller with selective apparent inertia is formulated to permit compliance in certain degrees of freedom while achieving precise trajectory tracking and disturbance rejection in others. Experiments demonstrate disturbance rejection, push-and-slide interaction, and on-board state estimation with depth servoing to interact with local surfaces. The system is also validated as a tool for contact-based non-destructive testing of concrete infrastructure.

An Omnidirectional Aerial Manipulation Platform for Contact-Based Inspection

Extending the maneuverability of multirotors promises to yield a considerable increase in their scope of applications, such as carrying out more challenging inspection tasks and generating complex, uninterrupted movements of an attached camera. In this article, we address the promise of multirotor maneuverability by presenting Voliro, a novel aerial platform that combines the advantages of existing multirotor systems with the agility of vehicles having omniorientational controllability. In other words, Voliro can fly in any direction while maintaining an arbitrary orientation.

The Voliro Omniorientational Hexacopter: An Agile and Maneuverable Tiltable-Rotor Aerial Vehicle

Extending the maneuverability of unmanned areal vehicles promises to yield a considerable increase in the areas in which these systems can be used. Some such applications are the performance of more complicated inspection tasks and the generation of complex uninterrupted movements of an attached camera. In this paper we address this challenge by presenting Voliro, a novel aerial platform that combines the advantages of existing multi-rotor systems with the agility of omnidirectionally controllable platforms. We propose the use of a hexacopter with tiltable rotors allowing the system to decouple the control of position and orientation. The contributions of this work involve the mechanical design as well as a controller with the corresponding allocation scheme. This work also discusses the design challenges involved when turning the concept of a hexacopter with tiltable rotors into an actual prototype. The agility of the system is demonstrated and evaluated in real- world experiments.

Voliro: An Omnidirectional Hexacopter With Tiltable Rotors

Interactions with articulated objects are a challenging but important task for mobile robots. To tackle this challenge, we propose a novel closed-loop control pipeline, which integrates manipulation priors from affordance estimation with sampling-based whole-body control. We introduce the concept of agent-aware affordances which fully reflect the agent's capabilities and embodiment and we show that they outperform their state-of-the-art counterparts which are only conditioned on the end-effector geometry. Additionally, closed-loop affordance inference is found to allow the agent to divide a task into multiple non-continuous motions and recover from failure and unexpected states. Finally, the pipeline is able to perform long-horizon mobile manipulation tasks, i.e. opening and closing an oven, in the real world with high success rates (opening: 71%, closing: 72%).

Learning Agent-Aware Affordances for Closed-Loop Interaction with Articulated Objects

Increasing robotic perception and action capabilities promise to bring us closer to agents that are effective for automating complex operations in human-centered environments. However, to achieve the degree of flexibility and ease of use needed to apply such agents to new and diverse tasks, representations are required for generalizable reasoning about conditions and effects of interactions, and as common ground for communicating with non-expert human users. To advance the discussion on how to meet these challenges, we characterize open problems and point out promising research directions. 

Paula Wulkop

Papers

The Voliro Omniorientational Hexacopter: An Agile and Maneuverable Tiltable-Rotor Aerial Vehicle

Voliro: An Omnidirectional Hexacopter With Tiltable Rotors

Learning Agent-Aware Affordances for Closed-Loop Interaction with Articulated Objects

It's Just Semantics: How to Get Robots to Understand the World the Way We Do