Soft Arm-Motor Thrust Characterization for a Pneumatically Actuated Soft Morphing Quadrotor

TL;DR

This paper addresses precise thrust characterization of a soft morphing quadrotor whose four SPA arms deform under differential pressure $ dp_i $ and are subjected to downwash from tip-mounted motors. It treats arm deflection angles $\\delta_i$ as dynamical states and uses controlled pressures $ dp_i $ to actuate the arms, while quantifying downwash effects via experiments. The authors develop an augmented state framework and derive empirical relations between $ dp_i $ and $\\delta_i$, highlighting the downwash-induced coupling that challenges conventional quadrotor control. The work lays the groundwork for a hybrid data-driven MPC approach to enable stable trajectory tracking in soft morphing UAVs.

Abstract

In this work, an experimental characterization of the configuration space of a soft, pneumatically actuated morphing quadrotor is presented, with a focus on precise thrust characterization of its flexible arms, considering the effect of downwash. Unlike traditional quadrotors, the soft drone has pneumatically actuated arms, introducing complex, nonlinear interactions between motor thrust and arm deformation, which make precise control challenging. The silicone arms are actuated using differential pressure to achieve flexibility and thus have a variable workspace compared to their fixed counter-parts. The deflection of the soft arms during compression and expansion is controlled throughout the flight. However, in real time, the downwash from the motor attached at the tip of the soft arm generates a significant and random disturbance on the arm. This disturbance affects both the desired deflection of the arm and the overall stability of the system. To address this factor, an experimental characterization of the effect of downwash on the deflection angle of the arm is conducted.

Figures (3)

• Figure 1: Soft drone with (a) unactuated soft arm and (b) pneumatically actuated soft arm.
• Figure 2: (a) The deflection angle of the soft arm with pneumatic actuation, and (b) experimental setup of the SMQ.
• Figure 3: Experimental results show the motion of the tip of the SPA in (a) the horizontal plane $XY$, vertical planes (b) $YZ$ and (c) $XZ$, and changes in the (d) angle in the vertical plane $\Theta_{i}$, (e) deflection angle $\delta_{i}$, and (f) angle in the vertical plane $\Phi_{i}$, with and without motor thrust for the same $dp_{i}$