Connecting the Physical Twin with a Digital Twin

This example can be used to connect the PiCar-X’s physical twin with a digital twin. The communication between both is established via MQTT. The MQTT server is part of the digital twin and you have to allow connections to port 1883 on the system where the MQTT server runs. This may requires adjustments to your firewall.

Adjust the environment files

There are three environment files with relevant variables:

  • picarx.env (on the Picar-X)
  • simulation-dt.env
  • picarx-dt.env

In this files you have to adjust the I2C devices (see Getting Started) and the MQTT server IP.

Start the Digital Twin

We assume at this point that the digital twin runs on a X64 Linux system (e.g. a server).

# Build and execute the Docker Containers
docker compose -f docker-compose-core.yml build 
docker compose -f docker-compose-dtsim.yml build 
docker compose -f docker-compose-dtsim.yml up

Start the Physical Twin

  • arm32v7 (RPi3)
  • arm64v8 (RPi4)
# First copy all content to the RaspberryPi4
scp -r ./ <user>@<picarx-ip>:~/

# Login to the RaspberryPi via ssh
ssh <user>@<picarx-ip>

# Build and execute the Docker Containers
TAG=latest ARCH=arm32v7 docker compose -f docker-compose-core.yml build 
TAG=latest ARCH=arm32v7 docker compose -f docker-compose-pt.yml build 
TAG=latest ARCH=arm32v7 docker compose -f docker-compose-pt.yml up  
# First copy all content to the RaspberryPi4
scp -r ./ <user>@<picarx-ip>:~/

# Login to the RaspberryPi via ssh
ssh <user>@<picarx-ip>

# Build and execute the Docker Containers
TAG=latest ARCH=arm64v8 docker compose -f docker-compose-core.yml build 
TAG=latest ARCH=arm64v8 docker compose -f docker-compose-pt.yml build 
TAG=latest ARCH=arm64v8 docker compose -f docker-compose-pt.yml up

Send Commands from the Digital Twin to the Physical Twin

You can operate the PiCar-X from its digital twin via:

# 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

# PUBLISH A MESSAGE TO TURN RIGHT WITH 50 percent motor speed
rostopic pub /picarx/drive/command picarx_msgs/Drive "{speed: 50, angle: 20}"

The PiCar-X should turn right by 20 degree and move in circles until you send another command.