Only the Digital Twin starts a simulation

If you want to develop new features for the PiCar-X’s digital twin and monitor the communication between the PiCar-X’s digital twin and the digital twin prototype, you can start the digital twin and a reduced digital twin prototype, which does not include the GAZEBO simulation. In that case, you can just use inside a Docker container of the digital twin prototype the echo function provided by ROS on the topic you want to monitor.

Adjust the environment files

There are three environment files with relevant variables:

  • picarx.env (for the DTP)
  • picarx-dt.env
  • simulation.env
  • simulation-dt.env

Start the Digital Twin with GAZEBO 

# Build Docker Containers if not previously done
docker compose -f docker-compose-core.yml build 
docker compose -f docker-compose-dtsim.yml build 

# Start the DT
docker compose -f docker-compose-dtsim.yml up

Start the Digital Twin Prototype without GAZEBO 

docker compose -f docker-compose-dtp-no-gazebo.yml up

To subscribe to any topic and get the content, you need to switch into one of the digital twin prototype’s Docker containers:

docker exec -it picar-x-ackermann_skill-dtp-1 /bin/bash

# INSIDE CONTAINER
source /root/catkin_ws/devel/picarx_ackermann_drive/setup.bash

There you can list all topics via:

rostopic list

Afterwards, you can subscribe to one of the topics, e.g. the command topic that receives all commands from the digital twin:

rostopic echo /picarx/drive/command

# The console should now print all incoming messages with the corresponding command from the DT.

Operate the Digital Twin Prototype from the Digital Twin

To operate the digital twin prototype, you need to switch into the container:

docker exec -it picar-x-ackermann_skill-dt-1 /bin/bash

# INSIDE CONTAINER
source /root/catkin_ws/devel/picarx_ackermann_drive/setup.bash

Inside the container you can publish a command message:

rostopic pub /picarx/drive/command picarx_msgs/Drive "{speed: 50, angle: 20}"

# The DT sends a command to the DTP and there the command is printed.