Start Digital Twin Prototype and Digital Twin with Separate Gazebo Simulation

In general it is always possible to start the digital twin prototype and digital twin on two different systems. Just make sure that the MQTT port 1883 is open on the digital twin side and that the MQTT clients have the IP of the MQTT server configured. In the following, we assume that you want to start the digital twin prototype and the digital twin on the same system with separate GAZEBO simulations for both. We further assume, that you can only create one I2C-stub chip.

In the Getting Started Guide, we create the I2C-stub with only one active address space (0x14). For this example, we have to register an additional address space (0x15). If you have already explored one of the other options, restart your system and execute:

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
sudo modprobe gpio-mockup gpio_mockup_ranges=1,41
sudo modprobe i2c-dev
sudo modprobe i2c-stub chip_addr=0x14,0x15

With the i2c-tools installed, you can check whether both addresses are allocated now:

i2cdetect -y 0      # the 0 represens /dev/i2c-0, insert the number of the stub here

# The result should be something like -- 14 15 --

Of course the idea of the digital twin prototype is that you use the same configuration as the original system, however, since all containers share the kernel modules of the system this example is executed and in most cases you cannot create two I2C-stub devices, they need to share the I2C device. In examples with serial or network protocols, this would be different.

The digital twin will use the address space 0x15 and two other GPIO pins.

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-same-system.yml build 

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

Start the Digital Twin Prototype with GAZEBO 

# Start the DTP
docker compose -f docker-compose-dtp.yml up

Operate the Digital twin Prototype

To operate the digital twin prototype, you need to switch into one of the digital twin’s 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 status should be sent automatically to the DTP and the PiCar-X moves in GAZEBO