The QuadSoft: Design, Construction, and Experimental Validation of a Soft and Actuated Quadrotor
Rodolfo Isaac VerdÃn MonzÃ3n, Hugo Alberto Moreno Jimenez, Mark Spong, Gerardo Flores
AI summary
Problem
Rigid quadrotors lack adaptability in cluttered environments, while existing morphing aerial platforms rely on complex discrete joints or custom control hardware that hinders real-world deployment.
Approach
The team designed a quadrotor with semi-rigid, tendon-driven flexible arms that continuously bend to modulate thrust direction, deriving a geometric mapping from servo input to curvature and validating it through outdoor flight tests.
Key results
- Tendon-driven continuum arms enable smooth in-flight reconfiguration without discrete joints
- Closed-form geometric mapping from servomotor input to arm curvature is derived and validated
- Outdoor flight tests demonstrate stable hover and morphology-induced horizontal translation under wind
- Platform maintains baseline stability and operates seamlessly on an unmodified PX4 autopilot
Why it matters
Demonstrates that soft morphing can be practically integrated into conventional UAVs, offering a scalable path toward adaptive, collision-resilient aerial systems for real-world navigation.
Abstract
This paper presents QuadSoft, a novel fully ac- tuated quadrotor equipped with continuous-curvature, tendon- driven soft robotic arms. The design combines a semi-rigid central frame with flexible arms, enabling controlled structural reconfiguration during flight without altering the propeller layout. Unlike existing soft aerial platforms that rely on discrete bending joints, QuadSoft utilizes a continuum deformation approach to modulate arm curvature, actively adjusting its thrust vector and aerodynamic characteristics. We charac- terize the geometric mapping between servomotor input and the resulting constant curvature, validating it experimentally. Outdoor flight tests demonstrate stable take-off, hover, direc- tional maneuvers, and landing, confirming that controlled arm bending can generate horizontal displacement while preserving altitude. Measurements of pitch, roll, and curvature angles show that the platform follows intended actuation patterns with minimal attitude deviations. These results demonstrate that QuadSoft preserves the baseline stability of rigid quadrotors while enabling morphology-driven maneuverability, all under the standard PX4 autopilot without retuning. Beyond a proof of concept, this work establishes a distinctive outdoor validation of a tendon-driven continuum morphing quadrotor, opening a new research avenue toward adaptive aerial systems that combine the safety and versatility of soft robotics with the performance of conventional UAVs. SUPPLEMENTARY MATERIAL A video showing the experimental results is also available at the following link: https://www.youtube.com/ watch?v=txPaA6l5GvE.