Bioinspired Soft Quadrotors Jointly Unlock Agility, Squeezability, and Collision Resilience

2025-11-07

AI Summary

Traditional rigid quadcopters suffer from poor collision resilience and limited passability through narrow apertures due to low compressibility. To address these limitations, this work draws inspiration from compliant biological wings and proposes an anisotropic stiffness design combined with a distributed mass–energy architecture, resulting in FlexiQuad—a soft-framed quadcopter. FlexiQuad is the first single-platform aerial robot to simultaneously achieve high agility (maximum speed >80 km/h; linear acceleration >3g), robust impact resistance (withstands 5 m/s frontal collisions), and exceptional compressibility (navigates apertures reduced to 70% of its original width), while reducing lateral collision forces by 39×. The prototype weighs 405 g and features tunable stiffness spanning 0.006–0.77 N/mm. Through dynamic modeling and experimental validation, FlexiQuad overcomes the longstanding trade-off barrier in soft aerial robotics, enabling concurrent optimization of agility, resilience, and deformability.

Technology Category

• Intelligent Robots: Multimodal Perception & Sensor Fusion
• Philosophy and Ethics of AI: Safety, Robustness & Trustworthiness
• Humans and AI: Planning and Decision Support for Human-Machine Teams

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Search and Retrieval-Augmented AI: Agentic search
• Systems and Infrastructure for Web, Mobile and WoT: Applied ML and AI for Web-based mobile applications

Abstract

Natural flyers use soft wings to seamlessly enable a wide range of flight behaviours, including agile manoeuvres, squeezing through narrow passageways, and withstanding collisions. In contrast, conventional quadrotor designs rely on rigid frames that support agile flight but inherently limit collision resilience and squeezability, thereby constraining flight capabilities in cluttered environments. Inspired by the anisotropic stiffness and distributed mass-energy structures observed in biological organisms, we introduce FlexiQuad, a soft-frame quadrotor design approach that limits this trade-off. We demonstrate a 405-gram FlexiQuad prototype, three orders of magnitude more compliant than conventional quadrotors, yet capable of acrobatic manoeuvres with peak speeds above 80 km/h and linear and angular accelerations exceeding 3 g and 300 rad/s$^2$, respectively. Analysis demonstrates it can replicate accelerations of rigid counterparts up to a thrust-to-weight ratio of 8. Simultaneously, FlexiQuad exhibits fourfold higher collision resilience, surviving frontal impacts at 5 m/s without damage and reducing destabilising forces in glancing collisions by a factor of 39. Its frame can fully compress, enabling flight through gaps as narrow as 70% of its nominal width. Our analysis identifies an optimal structural softness range, from 0.006 to 0.77 N/mm, comparable to that of natural flyers'wings, whereby agility, squeezability, and collision resilience are jointly achieved for FlexiQuad models from 20 to 3000 grams. FlexiQuad expands hovering drone capabilities in complex environments, enabling robust physical interactions without compromising flight performance.

Problem

• Developing soft quadrotors to overcome rigid drones' limitations
• Achieving agility, squeezability and collision resilience simultaneously
• Enabling robust flight performance in complex cluttered environments

Innovation

• Soft-frame quadrotor design inspired by biological organisms
• Achieves high agility with 3g acceleration and 80 km/h speed
• Enables squeezability through 70% gaps and fourfold collision resilience