A Soft-Bodied Aerial Robot for Collision Resilience and Contact-Reactive Perching

TL;DR

This work introduces SoBAR, a lightweight, inflatable soft-bodied aerial robot with tunable stiffness for intrinsic collision resilience and a passive hybrid fabric-based bistable (HFB) grasper for rapid contact-reactive perching. The design couples a soft inflatable frame that absorbs collisions with a bistable grasper that converts impact energy into a rapid curling grasp, enabling perching on objects of unknown shape and size. Through modeling, controlled experiments, and real-time autonomous perching trials, SoBAR demonstrates superior collision mitigation compared to rigid frames, high grasping power-to-weight ratios, and reliable perching on irregular and diverse surfaces, including concurrent wall collisions. These results highlight the potential of fully soft, fabric-based aerial robots to safely interact with humans and environments, enabling robust, energy-efficient perching and manipulation in unstructured settings, with future directions aimed at richer autonomy and further optimization of both body and grasper.”

Abstract

Current aerial robots demonstrate limited interaction capabilities in unstructured environments when compared with their biological counterparts. Some examples include their inability to tolerate collisions and to successfully land or perch on objects of unknown shapes, sizes, and texture. Efforts to include compliance have introduced designs that incorporate external mechanical impact protection at the cost of reduced agility and flight time due to the added weight. In this work, we propose and develop a light-weight, inflatable, soft-bodied aerial robot (SoBAR) that can pneumatically vary its body stiffness to achieve intrinsic collision resilience. Unlike the conventional rigid aerial robots, SoBAR successfully demonstrates its ability to repeatedly endure and recover from collisions in various directions, not only limited to in-plane ones. Furthermore, we exploit its capabilities to demonstrate perching where the 3D collision resilience helps in improving the perching success rates. We also augment SoBAR with a novel hybrid fabric-based, bistable (HFB) grasper that can utilize impact energies to perform contact-reactive grasping through rapid shape conforming abilities. We exhaustively study and offer insights into the collision resilience, impact absorption, and manipulation capabilities of SoBAR with the HFB grasper. Finally, we compare the performance of conventional aerial robots with the SoBAR through collision characterizations, grasping identifications, and experimental validations of collision resilience and perching in various scenarios and on differently shaped objects.

Figures (20)

• Figure 1: The overall operational scheme of SoBAR. (A) Flying and dynamic collision-based perching sequence. The woven fabric utilized is highlighted under a microscope. The magnification factor is 40x and aperture is 0.65. (B) The hybrid fabric-based bistable (HFB) grasper operating from a straight beam (prior to perching) to curled (perching) to recovery state (pneumatic recovery after perching). (C) Soft-bodied frame from a deflated stored state to an inflated and rigid state. (D) Head-on wall collision with SoBAR. (E) Grasping sequence of actuator takes 4$\mu$s and utilizes pneumatic actuation to recoil in approximately 3s. (F) Setting up and assembling SoBAR, approximately takes 4mins. (G) Dynamic perching to recovery to landing sequence of SoBAR. Video: https://youtu.be/Xgf67ZaSvRw
• Figure 2: The manufacturing process of SoBAR and the HFB actuators. (A) Fabrication steps for SoBAR. (i) First, align the woven fabric and heat-sealed actuator, after laser cutting. The woven fabric sheets are then sewn along the edges, utilizing a super-imposed seam, and the he heat-sealed actuator is inserted, to create the soft frame. (ii) Next, the pneumatic connector and 3D-printed motor mounts are added and aligned on the inflated soft-bodied frame. (iii) Finally, mount the propellers and motor pairs, electronics, and the perching mechanism. (iv) Possible perching mechanism orientations made of multiple HFB actuators (B) HFB actuator fabrication. (i) First, prepare the curling bistable mechanism by cutting and forming the spring steel metal. (ii) Next, curl the bistable tape spring, along its convex side, and restraining this position for a minimum of 30 min. (iii) The curling bistable tape spring. (iv) Finally, align the woven fabric, heat-sealed TPU actuator, TPU-coated nylon, three tape springs, and 3M grip material to create a single HFB actuator.
• Figure 3: Electronics diagram of SoBAR. On the right part of the diagram all the necessary components to achieve flight are illustrated. On the left part of the diagram the proposed electro-pneumatic components for the soft frame and perching grasper are shown.
• Figure 4: The complete closed-loop control pipeline of SoBAR for the perching task. The green blocks show the computation performed on the flight controller. The high-level companion computer is used to relay the position and orientation information of SoBAR from the indoor positioning system to the flight controller. The perching strategy, shown in the orange block, represents the state machine during an autonomous perching task. Mathematical conditions represent event-triggered transitions while the clock symbol represents the time-triggered ones. Here, $x_h$ refers to the hover target location for SoBAR directly above the perching target before initiating the descent. After the errors in position are within a tolerance region denoted by $\epsilon_x$, SoBAR initiates the descent trajectory. Once the grasper is engaged, the velocities are almost zero to indicate that the SoBAR has perched. After a user defined wait time, it then performs recovery control by first disengaging the grasper and then taking-off.
• Figure 5: Modeling arm deflection ($\theta_i$) versus internal pressure to estimate the thrust loss coefficient due to arm bending