how controlling the turtle in screen can help in controlling the robot in the real wold

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When you control turtle on your screen, ur publishing movement commands on a topic to which turtle is subscribed. In a similar way you can control a real bot by publishing velocity command on a topic to which bot is subscribed. You can use the same code just by changing the topic name provided datatype of topic is same. In most cases topic is of type "geometry_msgs::Twist".