Connecting the Physical Twin with a Digital Twin

This example can be used to connect the PiCar-X’s phyiscal twin with a digital twin. The communication between both is established via MQTT. The MQTT server is part of the digital twin.

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

# 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}"