Neither Fast Nor Slow: How to Fly Through Narrow Tunnels

TL;DR

This paper presents an autonomous multirotor system capable of smoothly navigating through narrow tunnels by generating optimized trajectories and analyzing flight dynamics, addressing control and perception challenges in confined spaces.

Contribution

It introduces a complete system with a motion planner for smooth trajectories and practical speed range estimation, validated through extensive real-world tunnel flights.

Findings

Successful autonomous flights in tunnels as narrow as 0.6 m

Trajectory planning based on Euclidean Distance Field

Flight data analysis informs speed and control strategies

Abstract

Nowadays, multirotors are playing important roles in abundant types of missions. During these missions, entering confined and narrow tunnels that are barely accessible to humans is desirable yet extremely challenging for multirotors. The restricted space and significant ego airflow disturbances induce control issues at both fast and slow flight speeds, meanwhile bringing about problems in state estimation and perception. Thus, a smooth trajectory at a proper speed is necessary for safe tunnel flights. To address these challenges, in this letter, a complete autonomous aerial system that can fly smoothly through tunnels with dimensions narrow to 0.6 m is presented. The system contains a motion planner that generates smooth mini-jerk trajectories along the tunnel center lines, which are extracted according to the map and Euclidean Distance Field (EDF), and its practical speed range is obtained through computational fluid dynamics (CFD) and flight data analyses. Extensive flight experiments on the quadrotor are conducted inside multiple narrow tunnels to validate the planning framework as well as the robustness of the whole system.