simulating multiple turtlebots in gazebo 1.9.3 ROS Hydro Ubuntu 12.04 [closed]

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I have read the following tutorials for multi-robot simulation purposes:

1    http://answers.ros.org/question/41433/multiple-robots-simulation-and-navigation/
2    http://answers.ros.org/question/65736/multiple-turtlebots-in-gazebo-how-to-solve-conflicts-in-multiple-cameras/

I am not getting tf for all the robots. The launch file for single robot is as follows:

<launch>
    <arg name="robot_name"/>
    <arg name="init_pose"/>
    <node name="spawn_minibot_model" pkg="gazebo" type="spawn_model" args="$(arg init_pose) -urdf -param /robot_description -model $(arg robot_name)" robot-namespace $(arg robot_name) respawn="false" output="screen"/> 

    <node pkg="robot_state_publisher" type="state_publisher" name="robot_state_publisher" output="screen">
    <param name="publish_frequency" type="double" value="30.0" />
    </node>
<!-- other nodes -->

</launch>

Gazebo complains with following error on spawning robot with the above mentioned command:

....
File /opt/ros/hydro/lib/python2.7/dist-package/rospy/msproxy.py line 117 in __getitem__ raise keyError(key)
KeyError "/robot_description"

If node is spawned without front slash of robot_description, multiple robots do appears on Gazebo, but Rviz onle show TF for one robot not other!!! The use Forward slash in front of robot_description is explained in tutorial 1.

Where I can read about all these parameters for Hydro version. ROSWiki do not provide much information about these parameters on http://wiki.ros.org/ROS/Tutorials/Ros... .