Onboard Safety Guarantees for Racing Drones: High-speed Geofencing with Control Barrier Functions

TL;DR

This paper presents a control barrier function-based method to ensure safety of high-speed racing drones, enabling real-time safety guarantees on lightweight hardware without compromising flight performance.

Contribution

It introduces an implicitly defined control barrier function leveraging backup controllers for practical, gradient-free safety enforcement on racing drones at high speeds.

Findings

Safe operation at speeds over 100 km/h demonstrated

Real-time safety guarantees achieved on a 10g micro-controller

Method maintains normal flight when no safety risks are present

Abstract

This paper details the theory and implementation behind practically ensuring safety of remotely piloted racing drones. We demonstrate robust and practical safety guarantees on a 7" racing drone at speeds exceeding 100 km/h, utilizing only online computations on a 10 gram micro-controller. To achieve this goal, we utilize the framework of control barrier functions (CBFs) which give guaranteed safety encoded as forward set invariance. To make this methodology practically applicable, we present an implicitly defined CBF which leverages backup controllers to enable gradient-free evaluations that ensure safety. The method applied to hardware results in smooth, minimally conservative alterations of the pilots' desired inputs, enabling them to push the limits of their drone without fear of crashing. Moreover, the method works in conjunction with the preexisting flight controller, resulting in unaltered flight when there are no nearby safety risks. Additional benefits include safety and stability of the drone when losing line-of-sight or in the event of radio failure.