Passive Fault Tolerance through Tension-to-Thrust Feed-Forward: Hybrid Input-to-State Stability for Decentralized Multi-UAV Slung-Load Transport under Abrupt Cable Severance

2026-05-06

AI Summary

This study addresses the lack of decentralized, coordination-free fault tolerance in multi-quadrotor slung-load systems during sudden cable failures, which hinders rapid load stabilization. The authors propose a passive fault-tolerant architecture that directly feedforwards locally measured cable tension into altitude thrust commands, combined with local PD sway suppression and a projection-based cascaded strategy to preserve trajectory tracking feasibility after faults. Theoretically, they establish a conditional hybrid input-to-state stability proof by integrating relaxed taut-cable reduction, Lyapunov jump boundedness, inter-fault decay, and periodic contraction, yielding an explicit recovery envelope. Simulations on a five-quadrotor system transporting a 10 kg payload show that under single- or dual-cable failures, the RMSE remains within 0.312–0.328 m, maximum sag is limited to 76.1–95.2 mm, and stability is recovered within one swing period; disabling the feedforward mechanism increases cruise error by 34–39% and sag by 3.6–4.0×.

Abstract

Abrupt cable severance in multi-UAV slung-load transport redistributes load and changes the active constraint set, leaving limited time for fault diagnosis and reconfiguration. Existing controllers rely on coordinated force allocation, peer-state exchange, or fixed cable topology, and therefore lack a certified decentralized recovery mechanism for unannounced severance. We present a passive architecture that routes each vehicle's measured cable tension directly into its altitude thrust command, $T_i^{\mathrm{ff}}=T_i$, while a surrounding proportional-derivative, anti-swing, and projection cascade preserves local tracking feasibility. The main contribution is a conditional hybrid practical input-to-state-stability certificate that composes a slack-excursion-bounded taut-cable reduction, bounded post-severance Lyapunov jumps, inter-fault decay, and per-fault-cycle contraction $ρ\in (0,1)$ into an explicit recovery envelope under stated actuator, slack, and dwell assumptions. We validate the controller in Drake multibody simulation with five vehicles, a 10 kg payload, Kelvin-Voigt cables, Dryden wind, and single- and dual-severance schedules: the closed loop attains 0.312-0.328 m RMSE, 76.1-95.2 mm peak sag, and recovery within one payload-pendulum period. Disabling the identity inflates cruise error by 34-39% and peak sag by 3.6x-4.0x, identifying local tension feed-forward as the dominant passive recovery mechanism in the tested decentralized cascade.

Problem

• multi-UAV slung-load transport
• abrupt cable severance
• decentralized control
• fault tolerance
• input-to-state stability

Innovation

• passive fault tolerance
• tension-to-thrust feed-forward
• hybrid input-to-state stability
• decentralized multi-UAV
• slung-load transport