MorphEUS: Morphable Omnidirectional Unmanned System

TL;DR

MorphEUS tackles the limitation of under-actuated multirotors by introducing a morphable co-axial quadrotor with independent thrust-vectoring per rotor arm, enabling true 6-DoF control. The approach combines translational and rotational dynamics with a generalized geometric controller and an energy-optimal control allocation, yielding full reachability and almost-everywhere exponential stability on $SO(3)$. Theoretical results on controllability and an energy-minimizing allocation are complemented by high-fidelity simulations demonstrating 6-DoF trajectory tracking, contact-based inspection, and navigation in constrained environments. The work promises enhanced dexterity, resilience to failures, and efficient operation for inspection and close-proximity imaging tasks in challenging settings.

Abstract

Omnidirectional aerial vehicles (OMAVs) have opened up a wide range of possibilities for inspection, navigation, and manipulation applications using drones. In this paper, we introduce MorphEUS, a morphable co-axial quadrotor that can control position and orientation independently with high efficiency. It uses a paired servo motor mechanism for each rotor arm, capable of pointing the vectored-thrust in any arbitrary direction. As compared to the \textit{state-of-the-art} OMAVs, we achieve higher and more uniform force/torque reachability with a smaller footprint and minimum thrust cancellations. The overactuated nature of the system also results in resiliency to rotor or servo-motor failures. The capabilities of this quadrotor are particularly well-suited for contact-based infrastructure inspection and close-proximity imaging of complex geometries. In the accompanying control pipeline, we present theoretical results for full controllability, almost-everywhere exponential stability, and thrust-energy optimality. We evaluate our design and controller on high-fidelity simulations showcasing the trajectory-tracking capabilities of the vehicle during various tasks. Supplementary details and experimental videos are available on the project webpage.

Figures (11)

• Figure 1: CAD of the proposed morphable quadrotor actuated with two additional degrees of freedom for each rotor, providing $360^{\circ}$ thrust-vectoring capabilities.
• Figure 2: Autonomous pipeline for the proposed variable-tilt morphable quadrotor.
• Figure 3: Schematic of the drone highlighting coordinate frames and servo angles.
• Figure 4: Force and torque envelopes, assuming that each arm can apply a maximum thrust of 20N. Force envelope assumes desired torque to be zero, and vice versa.
• Figure 5: Unit vectors in $\boldsymbol{i}_{\mathcal{B}}-\boldsymbol{j}_{\mathcal{B}}$ for yaw control.

Theorems & Definitions (5)

• Proposition 1: Reachability
• Corollary 1: Controllability
• Remark 1: Gimbal Lock
• Proposition 2: Exponential Stability Almost Everywhere in $SO(3)$
• Proposition 3: Energy-efficient Control Allocation