Turtlebot3 does not move autonomously in Gazebo

edit

I am trying out the turtlebot tutorial from this website https://automaticaddison.com/how-to-l...

when running this command roslaunch turtlebot3_gazebo turtlebot3_simulation.launch, my turtlebot3 does not move as expected.

After digging some threads in github, I added this line "turtlebot3_drive.init(); in the main function of "turtlebot3_drive.cpp" file

int main(int argc, char* argv[])
{
  ros::init(argc, argv, "turtlebot3_drive");
  Turtlebot3Drive turtlebot3_drive;
  turtlebot3_drive.init();  //the line that I added

  ros::Rate loop_rate(125);

  while (ros::ok())
  {
    turtlebot3_drive.controlLoop();
    ros::spinOnce();
    loop_rate.sleep();
  }

  return 0;
}

The problem still persists, may anyone help me with it?