Onboard Computer Setup

Setup routine and scripts for the ATMOS free-flyers’ onboard computers (OBC). For ATMOS, we consider the NVIDIA Jetson Orin NX as the OBC, but these instructions can be roughly follower for other Ubuntu 22.04 OBCs.

Jetson Setup

These instructions assume that the Jetson is running Ubuntu 22.04 on Jetpack 6. Then, install ROS 2 Humble:

Follow installation instructions at https://docs.ros.org/en/humble/Installation/Ubuntu-Install-Debians.html

Source ROS 2 by default

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

Lastly, clone:

git clone git@github.com:DISCOWER/FF_OBC_Setup.git $HOME/FF_OBC_Setup

If cloning fails due to SSH authentication, make sure the OBC has GitHub SSH keys configured. See GitHub’s guide to generating SSH keys for instructions.

Set the hostname

Change the hostname by replacing <hostname> with the desired name.
```
sudo hostnamectl set-hostname <hostname>
```
Edit the /etc/hosts file.
```
sudo vim /etc/hosts
```
Find the line that starts with 127.0.0.1 or 127.0.1.1 followed by the old hostname (probably discower) and change it to the new hostname. Save and close the file.

Set up ROS 2 Workspace

Here we provide an example of a workspace setup for the PX4 communication and the vehicle’s odometry. Note that our interface was tested on a Qualisys motion capture setup using the repository in https://github.com/DISCOWER/motion_capture_system. For motion capture systems with different coordinates, you may need to adjust the srl_vehicle_mocap_odom package.

Set up workspace. Clone and build required ROS 2 packages.

mkdir -p ~/atmos_ws/src/
cd ~/atmos_ws/src/
git clone git@github.com:PX4/px4_msgs.git
git clone git@github.com:DISCOWER/srl_vehicle_mocap_odom.git
cd ~/atmos_ws
colcon build

Install Micro-XRCE-DDS-Agent

Install with snap-store

sudo snap install micro-xrce-dds-agent --edge

Set up Micro-XRCE-DDS-Agent as a service:

sudo snap set micro-xrce-dds-agent daemon=true
sudo snap set micro-xrce-dds-agent transport=udp4
sudo snap set micro-xrce-dds-agent port=8888
sudo systemctl enable snap.micro-xrce-dds-agent.daemon.service

For Serial Communication: for serial communication between PX4 and the onboard computer, change the transport to serial and set the corresponding parameters:

sudo snap set micro-xrce-dds-agent daemon=true
sudo snap set micro-xrce-dds-agent transport=serial
sudo snap set micro-xrce-dds-agent device=<obc-serial-port>
sudo snap set micro-xrce-dds-agent baudrate=<your-baudrate-from-PX4>
sudo systemctl enable snap.micro-xrce-dds-agent.daemon.service

Add PX4 Rules for USB Mavlink interface

These rules assume that the PX4 is connected via USB to the onboard computer. To add the udev rules, run:

sudo cp $HOME/FF_OBC_Setup/rules/* /etc/udev/rules.d/
sudo udevadm control --reload-rules
sudo udevadm trigger

Add MAVProxy and Mavlink Router

Follow these instructions to install the mavlink-router:

sudo apt install git meson ninja-build pkg-config gcc g++ systemd
sudo pip3 install meson
git clone git@github.com:mavlink-router/mavlink-router.git ~/mavlink_router
cd ~/mavlink_router
git submodule update --init --recursive
meson setup build .
sudo ninja -C build install
sudo mkdir -p /etc/mavlink-router/
sudo cp $HOME/FF_OBC_Setup/mavlink.conf/* /etc/mavlink-router/

Add the startup service

These services will auto-start the motion capture odometry node and the mavlink-router on boot. Note that the ROS2 node in srl_vehicle_mocap_odom might require modifications for your application and laboratory setup.

sudo cp $HOME/FF_OBC_Setup/services/* /etc/systemd/system/
sudo systemctl daemon-reload
sudo systemctl enable vehicle_mocap_odom
sudo systemctl start vehicle_mocap_odom
sudo systemctl enable mavlink-router
sudo systemctl start mavlink-router

Add a Static IP for the PX4 Ethernet

Set a static IP-address for the PX4 ethernet connection. This is done via NetworkManager on the onboard computer. We are using 192.168.0.1.

Open a terminal and check existing network connections:
```
nmcli connection show
```
Identify the connection used for the PX4.
Open the connection’s configuration file in a text editor:
```
sudo vim /etc/NetworkManager/system-connections/<your-wired-connection>.nmconnection
```
Replace <your-wired-connection> with the actual connection name.

Modify the configuration file to set a static IP. The settings should include:

[connection]
id=<your-wired-connection>
uuid=<generated-uuid>
type=ethernet

[ipv4]
address1=192.168.0.1/24,192.168.0.254
method=manual

[ipv6]
addr-gen-mode=stable-privacy
method=auto

Save the file and restart NetworkManager:
```
sudo systemctl restart NetworkManager
```

All set!

At this point, you can reboot the system and the services should start automatically. You can check if all ROS 2 topics are available with:

ros2 topic list

The FMU topics should be populated. You can check if the communication is successful by subscribing to vehicle_attitude:

ros2 topic echo /fmu/out/vehicle_attitude

Lastly, on the Ground Control Station (a personal laptop, for instance), open QGroundControl, add a TCP Comm Link to the IP of the vehicle (leave the port as default) and check for connection. QGroundControl should report the vehicle status.