Px4

PX4 is an open-source autopilot software stack for unmanned aerial vehicles (UAVs) and other autonomous aircraft and ground vehicles. It provides flight control firmware, a development framework, and integration with ground control software and simulation tools. The stack is designed to be hardware-agnostic and supports a range of vehicle configurations, including multirotors, fixed-wing aircraft, and vertical takeoff and landing (VTOL) platforms.

Origins and governance: PX4 originated in the mid-2010s as a collaborative effort among researchers and developers, notably at ETH Zurich, and is maintained under the Dronecode Foundation, part of the Linux Foundation. It is released under a permissive open-source license (BSD 3-Clause). The project is widely used in both research and commercial deployments and is one of the major open-source drone autopilot projects alongside ArduPilot.

Architecture and features: The firmware runs on the NuttX real-time operating system and uses the uORB messaging system for inter-module communication. Its modular architecture includes sensor drivers, state estimation (e.g., EKF-based estimators), flight control laws, mission planning, and safety features. PX4 communicates with ground control stations via MAVLink and supports software-in-the-loop and hardware-in-the-loop simulations. It integrates with Gazebo-based SITL for simulation and with ground stations such as QGroundControl.

Hardware compatibility and ecosystem: PX4 supports a wide range of flight controllers, notably Pixhawk and its successors, as well as newer hardware platforms. The project maintains extensive documentation, developer guidelines, and a large global community contributing code, tutorials, and professional support. The PX4 ecosystem includes companion computer integration for advanced autonomy and perception tasks.