(ROS2 Turtlebot3 tutorial) How am I able to move my turtlebot just by builiding an Action Graph(omni graph) and without executing a launch file?

I am new to ROS2 so this could be considered a newbie question so please bear with me.

I am going through Isaac Sim tutorials for ROS2 and there is something that I just cant wrap my head around and that is the tutorial for driving the turtlebot via ROS2 messages.
(link: 2. Drive TurtleBot via ROS2 messages — Omniverse Robotics documentation)

In this tutorial, the instructions are:

  1. Import turtlebot3 URDF file and load the robot model in Isaac Sim.
  2. Build an Action Graph
  3. move/drive the turtlebot via ROS2 messages
    • option a : publish a twist message to /cmd_vel topic to control the robot
    • option b : run the teleop keyboard program and send twist messages via keyboard

What i do not understand is, how does this work without a “launch file” or a ROS2 run command regarding the turtlebot that was imported in to the simulation scene??
(other ROS2 tutorials for Isaac Sim have executable launch files that run the ROS2 nodes and render the 3d model of the robot on to the scene but the tutorial for Turtlebot3 somehow does not follow this procedure.)

Does the “play” button in Isaac Sim somehow automatically “launch”/“run” the nodes for the turtlebot??

I have read the documentation for OmniGraph and I am having trouble understanding what is actually happening under the hood when I build an Action Graph to drive the turtlebot in this tutorial.

Can someone please explain whats happening here? Thank you!

Are u understand now? I want to know too.

Hi @jaeyeun and @violet , thank you for your question. The other Isaac Sim ROS launch files are typically for more complex tasks (like navigation where multiple parameters need to be set and passed to the nav2 stack when launching it)

To answer your question, yes when you hit play all your ROS OmnigraphNodes will launch (as long as they are correctly setup and connected to the playback tick node). Please take a look at this video for reference, I have walked through the steps