Understanding rbcar response in Gazebo

[prasgane]

I am analysing the response to rbcar in Gazebo by giving an open loop velocity commands and comparing it with the actual velocity of rbcar using the /gazebo/model_states topic and I am noticing a a steady state error in the said response (refer to plot below). I naturally tried to change the gains in rbcar.yaml but that doesn't seem change the response that much.

My questions are:

1. In rbcar_robot_control, the velocity for each wheel is computed using ref_speed_joint = 2.0 * v_ref_ / RBCAR_WHEEL_DIAMETER. Could you help me understand the math behind this?
2. Could you also help me understand how you arrived at the gains in rbcar_control.yaml? Can I interpret these gains as an abstraction of how the actual rbcar hardware converts the velocity commands to AC motor voltages and so on?