ROS Installation

The version of the installed OS is based on Ubuntu 20.04 for which the latest version of ROS1 is ROS Noetic. To install it, the official guide in the ROS wiki was followed.

1. Setup sources.list

   sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu $(lsb_release -sc) main" > /etc/apt/sources.list.d/ros-latest.list'
   

2. Setup keys

   sudo apt install curl
   curl -s https://raw.githubusercontent.com/ros/rosdistro/master/ros.asc | sudo apt-key add -
   sudo apt update
   

3. Installation (the desktop-full variant was selected for this specific installation)

   sudo apt install ros-noetic-desktop-full
   

4. Environment setup

   echo "source /opt/ros/noetic/setup.bash" >> ~/.bashrc
   source ~/.bashrc
   

5. Dependencies for building packages

   sudo apt install python3-rosdep python3-rosinstall python3-rosinstall-generator python3-wstool build-essential
   
   sudo rosdep init
   rosdep update
   

MAVROS

To communicate with the flight computer (running the PX4 autopilot) using the MAVLink protocol through ROS, the MAVROS package was used. It is assumed that the flight computer is connected to the onboard computer through USB.

sudo apt install ros-noetic-mavros
sudo apt install ros-noetic-mavros-extras
cd /opt/ros/noetic/lib/mavros
sudo ./install_geographiclib_datasets.sh 

Additionally, to allow access to the USB ports for serial communication with the flight computer, these commands are needed:

sudo gpasswd -a $USER dialout
sudo reboot now

The package can now be tested by running roslaunch mavros px4.launch and verifying that data is being published in the available ROS topics (rostopic list and rostopic echo ...).

The MAVROS package also allows to redirect the MAVLink communications to another computer, where QGroundControl can be used for example. To do this, an option can be included when calling the launch file - roslaunch mavros px4.launch fcu_url:=/dev/ttyACM0:57600 gcs_url:=udp://@${GCS_IP}:${GCS_PORT}, where fcu_url is where the flight computer is connected, GCS_IP is the IP of the computer that wants to access the MAVLink communications and GCS_Port is an arbitrary port.

MAVROS Example

1. Onboard computer IP: 192.168.1.126;
2. Flight computer connected to onboard computer through USB (/dev/ttyACM0);
3. Other computer IP: 192.168.1.118;
4. Run roslaunch mavros px4.launch fcu_url:=/dev/ttyACM0:57600 gcs_url:=udp://@192.168.1.118:15001 on the onboard computer;
5. Run roslaunch mavros px4.launch fcu_url:=udp://:15001@ gcs_url:=udp://@localhost:15002 on the other computer;
6. rostopic list and rostopic echo ... on the other computer will show the data from the flight computer;
7. QGroundControl can be used on the other computer on port 15002.