ROS Tracked Robot Gazebo Simulation

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Hello, I am quite new to ROS and currently making a track robot model for gazebo & rviz simulation.

I have finished making the meshes of my robot with wheels and managed to make a basic URDF file. First Question. Now I am wondering how do I add the track model to the URDF file. Do I just make another mesh of the whole chain and add it just as I did with the wheels? (what will be the joint type and where do I position the joint?) Second Question. If I did add the chain and simply fixed its position. How will the chain move such that it moves in relation to the wheels? I have checked the following links but I am learning them step by step.

1. track Robot Gazebo-ROS
2. Problems in simulating a tracked vehicle and spawning the model
3. Track Robot Plugin
4. Parameters for a skid steering robot