ROS2 based Sensor Readout on Raspberry Pi

Description

The aim of the project is to publish and subscribe messages between a ROS2 Jazzy (local machine) and a remote node (Raspberry Pi Zero 2). The local machine and Pi may be in different networks. Thus, SSH port forwarding is used to maps the port to the same network. On the Pi the roslibpy Python library is used to communicate with ROS2 since it does not require a ROS2 installation on the Pi. But it requires a ros-bridge-server on the local machine.

Setup and Usage

1. Docker setup on local machine with Dockerfile & docker-compose

   • The setup follows the tutorial Setup-ROS-2-with-VSCode-and-Docker-Container but without using a display. The "postCreateCommand" command automatically install the required dependencies of the ROS2 packages.
   • Install the ros-bridge-server which runs default on port "9090". Thus map the port to localhost in docker-compose file
   • (optional) To Persist bash history

2. Connect from the local machine to the Pi with the following SSH config:

   Host myPi
       HostName XXX
       User Pi
       Port 22
       IdentityFile ~/.ssh/XXX
       IdentitiesOnly yes
       LocalForward 8086 localhost:8086
       RemoteForward 9090 localhost:9090
   

   Important is to use "RemoteForward" to make the ros-bridge-server (Port 9090) available at the Pi. The "LocalForward" of port 8086 makes an InfluxDB database with all Pi`s sensor data available at the local machine.

   If you use VS Code for SSH make sure that all extensions (Python, etc.) are deactivated on the Pi. Otherwise the Pi crashes due to heavy load.

3. Starting the ROS2 nodes on the local machine

   • For the first startup build all ROS packages with

     colcon build
     

   • Start all ROS2 nodes with

     docker compose up -d
     

   • Attach terminal to the running container with

     docker attach container_name
     

     This way the entrypoint (/ros_entrypoint.sh) is automatically executed. If you have to create a new terminal you must always first execute

     docker exec -it container_name bash 
     source /opt/ros/jazzy/setup.bash
     

     to source the environment and enable to ros2 command.

4. Test the setup by starting a ros-bridge server, a simple listener and a talker (Pi) using docker compose or execute to following steps manually

   • Start the ros-bridge-server

     ros2 launch rosbridge_server rosbridge_websocket_launch.xml
     

   • Start the listener to log the messages on the terminal

     ros2 run py_pubsub listener
     

   • Start the talker on the Pi

Working with ROS2 Python packages

• Follow the instructions: Writing-A-Simple-Py-Publisher-And-Subscriber

• Create a ROS2 package py_pubsub in the standard directory ./src to automatically creates the required folder structure.

  ros2 pkg create --build-type ament_python --license Apache-2.0 py_pubsub
  

• Add all the dependencies of the package to the file ./src/py_pubsub/package.xml

• Add the entrypoints (talker and listener) in the setup file ./src/py_pubsub/setup.py

• Install the required dependencies of the ROS2 packages

  sudo rosdep update && sudo rosdep install --rosdistro=jazzy --from-paths src --ignore-src -y
  

• Build the package

  colcon build --packages-select py_pubsub
  

• Execute a package in a new terminal with

  source /opt/ros/jazzy/setup.bash
  source install/setup.bash
  ros2 run py_pubsub talker
  

Python development of ROS2 packages

Can be done with the VSCode devcontainer extension and proper settings in .devcontainer/devcontainer.json file. To enable the Python Code-Checking features, provide the paths to the installed Python environment, side-packages and ROS2 packages.

Create custom ROS2 messages

• Follows the tutorial Creating custom msg and srv files

• Create a package

  ros2 pkg create sensor_msgs --build-type ament_cmake
  

• Add a src/sensor_msgs/msg directory in the package and add a create the custom message file, e.g., src/sensor_msgs/msg/ENS160.msg

• Modify the CMakeList.txt with the following com

  find_package(rosidl_default_generators REQUIRED)
  rosidl_generate_interfaces(${PROJECT_NAME}
      "msg/ENS160.msg"
      "msg/ENS210.msg"
      "msg/WH2600.msg"
  )
  

• Modify the package.xml with

  <build_depend>rosidl_default_generators</build_depend>
  <exec_depend>rosidl_default_runtime</exec_depend>
  <member_of_group>rosidl_interface_packages</member_of_group>
  

• Build the package with

  colcon build
  source install/setup.bash