Synergistic Morphology and Feedback Control for Traversal of Unknown Compliant Obstacles with Aerial Robots

Abstract

Animals can traverse vegetation by direct physical interaction using their entire body to push aside and slide along compliant obstacles. Current drones lack this interaction versatility that stems from synergies between body morphology and feedback control modulated by sensing. Taking inspiration from nature, we show that a task-oriented design allows a drone with a minimalistic controller to traverse obstacles with unknown elastic responses. A discoid sensorized shell allows contact to be established and sensed anywhere along the shell and facilitates the sliding along the obstacle. This simplifies the formalization of the control strategy, which does not require a model of the interaction with the environments, nor high-level switching conditions for alternating between pushing and sliding, thereby reducing the computational burden. Indeed, we exploit an optimization-based controller that only ensures safety constraints on the state of the robot and dampens the oscillations of the environment during the interaction, even if the elastic response is unknown and variable. Experimental evaluation, using a hinged surface with three different stiffness values ranging from 18 to 155.5 Nmm/rad, validates the proposed strategy and the necessity for the synergic task-oriented design and feedback control. By also showcasing the traversal of real branches, this work makes an initial contribution toward drone flight across cluttered vegetation, with relevant applications in environmental monitoring, precision agriculture, and search and rescue.