Fifty planes in the air running ROS & Gazebo
The Advanced Robotic Systems Engineering Lab at the Naval Postgraduate School in Monterey, CA recently flew fifty small autonomous planes together using ROS.
Each plane – a styrofoam wing with a 56” wingspan – was equipped with a Pixhawk autopilot running a modified version of the open-source Ardupilot firmware and an ODroid u3 “payload” computer running ROS Indigo. The payload used autopilot_bridge (similar to mavros) to bridge between serial communications with the autopilot and ROS messages and services. A network node bridged ROS communications with a lightweight UDP-based protocol that allowed aircraft to share their pose and status with one another and to receive commands from the ground.
Also residing on the payload was a set of controller nodes that could “drive” the plane by sending updated target latitude-longitude-altitude commands to the autopilot. Controllers were individually activated by a state machine, based on commands from the ground. The controller used during the fifty-plane flight was a follower controller. A single ground operator commanded two sets of 25 planes each to configure themselves into leader-follower formations; planes would determine a leader based on highest altitude (which was deconflicted at the start of the flight). The leader would then proceed along a predefined racetrack, and all followers, listening to the broadcast position of the leader, would track its path while remaining at their designated altitudes.