I am using melodic and ubuntu 18.04 and gazebo-9.
Problem: When I give the command of turning the Yaw (angle around z axis) as a positive value eg (+0.3), the model should rotate anticlockwise (ie towards its left). But it is moving clockwise.
Question: Why, my robot does not rotate anticlockwise, when I give it a positive rotation command?

I downloaded urdf file of a model (two-wheeled robot) from part1 of
this site and added plugin "libgazeborosdiffdrive.so"
My launch file is as follows:

<xml version="1.0" encoding="UTF-8"?>
<launch>
    <param name="robotdescription" command="$(find xacro)/xacro.py '$(find m2wrdescription)/urdf/m2wrwebsite.urdf'" >


&lt;arg name="x" default="0"/&gt;
&lt;arg name="y" default="0"/&gt;
&lt;arg name="z" default="0.5"/&gt;

&lt;include file="$(find gazebo_ros)/launch/empty_world.launch"&gt;
&lt;/include&gt;

&lt;node name="mybot_spawn" pkg="gazebo_ros" type="spawn_model" output="screen"          args="-urdf -param robot_description -model m2wr -x $(arg x) -y $(arg y) -z $(arg z)" /&gt;


</launch>

I am setting rotation of the model from this python script, using topic=cmd_vel and creating a publisher node. I tried to give the code of my script here. But I think, my length exceeds, so I am not including it.