Modelling, Analysis and Control of OmniMorph: an Omnidirectional Morphing Multi-rotor UAV

TL;DR

OmniMorph presents a morphing multi-rotor platform that transitions between underactuated and omnidirectional operation via a single synchronized tilting angle $\alpha$, enabled by eight bi-directional propellers arranged on a cube around the center of mass. A Newton–Euler dynamic model with an actuation wrench $\mathbf{w}(\boldsymbol{u}) = \mathbf{A}(\alpha) \boldsymbol{u}_w$ and a full allocation matrix framework captures the dependence of actuation on $\alpha$, with a rank analysis showing underactuation at $\alpha=0$ and near-full actuation elsewhere. A novel control scheme solves constrained optimization problems to select $\alpha^*$ and rotor speeds $\boldsymbol{u}_w^*$, balancing input effort and tracking error while allowing mode transitions; simulations in Gazebo and preliminary prototype tests validate the approach and examine propeller interference. The work demonstrates potential gains in energy efficiency and dexterity for aerial manipulation, outlining a path toward real-world morphing UAVs with reduced payload and maintenance, plus robust performance under aerodynamic disturbances and component degradation.

Abstract

This paper introduces for the first time the design, modelling, and control of a novel morphing multi-rotor Unmanned Aerial Vehicle (UAV) that we call the OmniMorph. The morphing ability allows the selection of the configuration that optimizes energy consumption while ensuring the needed maneuverability for the required task. The most energy-efficient uni-directional thrust (UDT) configuration can be used, e.g., during standard point-to-point displacements. Fully-actuated (FA) and omnidirectional (OD) configurations can be instead used for full pose tracking, such as, e.g., constant attitude horizontal motions and full rotations on the spot, and for full wrench 6D interaction control and 6D disturbance rejection. Morphing is obtained using a single servomotor, allowing possible minimization of weight, costs, and maintenance complexity. The actuation properties are studied, and an optimal controller that compromises between performance and control effort is proposed and validated in realistic simulations. Preliminary tests on the prototype are presented to assess the propellers' mutual aerodynamic interference.

Figures (12)

• Figure 1: OmniMorph: ua configuration (left) and od configuration (right).
• Figure 2: Sets of feasible forces for different values of $\alpha$. The three components of the thrust in the body frame are displayed. OmniMorph is omnidirectional when a sphere with a radius equal to the robot's weight is inscribed inside the polytope of feasible forces.
• Figure 3: Representation of OmniMorph in which the axes of rotation of the propellers, lying along the cube edges, are highlighted.
• Figure 4: For a given fixed propeller tilting angle $\alpha_f$, a morphing design is convenient, provided that the relative mass of the tilting mechanism is lower than $\bar{\Delta}_m$
• Figure 5: Radius of the maximum inscribed sphere is the feasible force set in Figure \ref{['fig:feasible_forces']} for different values of $\alpha$.When this is equal to its weight, OmniMorph can sustain its weight in all orientations.