  The paper presents a presents a framework for fire extinguishing in an urban
scenario by a team of aerial and ground robots. The system was developed for
the Challenge 3 of the 2020 Mohamed Bin Zayed International Robotics Challenge
(MBZIRC). The challenge required to autonomously detect, locate and extinguish
fires in different floors of a building, as well as in the surroundings. The
multi-robot system developed consists of a heterogeneous robot team of up to
three Unmanned Aerial Vehicles (UAV) and one Unmanned Ground Vehicle (UGV). The
paper describes the main hardware and software components for UAV and UGV
platforms. It also presents the main algorithmic components of the system: a 3D
LIDAR-based mapping and localization module able to work in GPS-denied
scenarios; a global planner and a fast local re-planning system for robot
navigation; infrared-based perception and robot actuation control for fire
extinguishing; and a mission executive and coordination module based on
Behavior Trees. The paper finally describes the results obtained during
competition, where the system worked fully autonomously and scored in all the
trials performed. The system contributed to the third place achieved by the
Skyeye team in the Grand Challenge of MBZIRC 2020.
