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

Abstract

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. Index Terms-Aerial systems: Applications, aerial systems: mechanics and control, motion control, robust/adaptive control of robotic systems. I. INTRODUCTION Q UADROTORS are disrupting industries ranging from agriculture to transport, security, infrastructure, entertainment, and search and rescue [1]. Their maneuverability and hovering capabilities allow them to navigate through complex structures, inspect damaged buildings, and even explore underground tunnels and caves. Yet, current quadrotors still lack the

The current state and future outlook of rescue robotics

“…Unmanned aerial robots offer many benefits for rescuers in a disaster scenario. Their overhead perspective can be useful for surveying and situational awareness (Erdelj, Natalizio, Chowdhury, & Akyildiz, ; Marconi et al, ), but they can also navigate through small spaces or fly over obstacles that may be obstructed for ground‐based platforms (Falanga, Mueggler, Faessler, & Scaramuzza, ; Falanga, Kleber, Mintchev, Floreano, & Scaramuzza, ). However, their size and power constraints often mean that their sensor payloads are restricted and their flight time is low, and their fragility requires precise perception and control to avoid collisions or collision tolerant designs, potentially limiting their effectiveness in disaster scenarios.…”

“…Aggressive drone flight through narrow gaps can be achieved with dynamic trajectories and active vision (left; Falanga et al, ). A target application for this approach would be to enable a flying robot to enter structures such as earthquake‐damaged buildings through small apertures in an emergency response (right; Falanga et al, ) [Color figure can be viewed at wileyonlinelibrary.com]…”

ARDEA—An MAV with skills for future planetary missions

“…This can be simply addressed by constraining the size of the vehicle or by changing the shape of the frame on the fly. Those designs have one additional degrees of freedom (DOF) per frame arm and have been shown to either change the frame shape during flight in an adaptive morphology way (Falanga, Kleber, Mintchev, Floreano, & Scaramuzza, 2019) or by steering the motor thrust vectors in a way that the MAV can fly and hover in arbitrary orientations (Kamel et al, 2018) and therefore, pass narrow passages.…”

Evaluation of a Baseline Controller for Autonomous “Figure-8” Flights of a Morphing Geometry Quadcopter: Flight Performance

“…In this effort, a custom developed MRAC flight control algorithm was implemented to accommodate for the uncertainties resulting from morphing geometry. In [ 29], the authors explore the morphing by pivoting individual arms, thus generating what they term as "H", "O" and "T" morphologies and evaluated the performance of the quadcopter in both hover conditions and while executing circular trajectories. As with most of the other approaches, a customized Linear Quadratic Regulator (LQR) controller was implemented to maintain the stability and performance of the quadcopter in its morphed configurations.…”