ROS2-PX4-Offboard

ROS2 node examples for bi-directional interfacing with PX4 and implementing custom offboard control algorithms.

Based on source code from PX4 and Jaeyoung Lim.

Setup

This is intended to be used on a companion computer or workstation running Ubuntu 22.04.

External Dependencies

Refer to the official PX4 setup guide for ROS2:

• Installation and setup of the PX4 developement environment is not strictly required but is recommended for simualtion purposes and source code.
  • Note that this project is developed for and tested with the upcomming version 1.15 of PX4 for full support of the uXRCE-DDS interface.
• Install ROS2 Humble.
• Install the Micro XRCE-DDS Agent.

ROS Node Setup

1. Clone this example repository: git clone https://github.com/GHowardEng/ROS2-PX4-Offboard.git --recursive

• The dds_topics.yaml file provided is a modified copy of the vanilla version from PX4-Autopilot/src/modules/uxrce_dds_client with a number of additional topics added.
  • You may use the vanilla version of this file already included in the PX4-Autopilot reposity - most telemetry and commands are already present.
  • If you wish to use the custom version for addition topics, you must replace the file in your local copy of the PX4 repo, and generate a custom build of the firmware (upload to your target hardware if required).
  • You may add or remove topics as desired for your application.

2. IMPORTANT: Verify px4_msgs is synchronized with the specific version of PX4-Autopilot being used!

• A version of the px4_msgs repo is included as a submodule in the ws_offboard_example/src folder. This should be compatible with PX4 version v1.15.0-rc1

• If using another major release, you may checkout the branch assoicated with this release version in the px4_msgs submodule (e.g. 1.14)

• If using any other version, such as running PX4 from the main branch, or encounter message compatibility issues, you should manually synchronize the message definitions:

  • Checkout the correct branch/tag of the PX4-Autopilot repo you wish to interface with.
  • Delete all *.msg files in workspace src/px4_msgs/msg/ folder and copy all *.msg files from PX4-Autopilot/msg/ in it. Assuming that this repository and the PX4-Autopilot repository are placed in your home folder, you can run:

  rm -f ~/ROS2-PX4-Offboard/ws_offboard_example/src/px4_msgs/msg/*.msg
  cp ~/PX4-Autopilot/msg/*.msg ~/ROS2-PX4-Offboard/ws_offboard_example/src/px4_msgs/msg/
  

3. Build the ROS node:

• Navigate to the ws_offboard_example folder
• If not done already, the terminal instance you are using must be setup for the ROS environment: source /opt/ros/humble/setup.bash
• Run a build with colcon build. This will build all packages under the /src folder.
• Note there are some conflicts building with newer versions of setuptools package. Depending on the version you have installed, you may need to downgrade (version 69.5.1 is known to work successfully)

Running

1. PX4 and uXRCE-DDS Client:

• If running software-in-the-loop (SITL), start a PX4 SITL instance on your machine with make px4_sitl gz_rc_cessna.
  • The uXRCE-DDS client is started automatically on a SITL instance, with network configuraiton localhost:8888.
• If running with real PX4 hardware, make an ethernet connection between the companion device and autopilot hardware.
  • Boot up the autopilot and access the system shell (MAVLink Console in QGroundControl).
  • Start the uXRCE-DDS client with uxrce_dds_client start -h <Companion IP> -p <Port> (note this assumes UDP protocol).

2. uXRCE-DDS Agent (on companion device):

• From a new terminal instance, boot the agent with MicroXRCEAgent udp4 -p <Port> (matching port selected with PX4's client).
• At this point, notifications should be printed on both the PX4 shell (client-side) and terminal instance (agent-side) showing that topics are being published and recieved.
• Note that uXRCE-DDS agent initialization may be automated on Ubuntu by adding the command to 'Startup Applications Preferences'.

3. ROS Node:

• From the ws_offboard_example folder, the node may be started with the provided start-up script: ./startNode.sh.
• You should see notifications from the subscriber callback functions indicating that the various topics are being recieved.

4. Activate Offboard Mode:

• Arm the vehicle and takeoff (if in simulation). The ROS node should detect the arming event.
• Switch PX4 to Offboard mode via QGroundControl or using commander in the PX4 system shell.
• The ROS node should detect the mode change, and begin sending attitude commands to the autopilot.
  • The example behavior is to command a pitch attitude of 0 degrees, and a roll sinusoid of +/- 15 degrees with a throttle value of 50%.