I am running a multi-robot simulation platform with each robot's nodes,parameters,topics,etc. in a separate namespace (eg. /robot1/robot_description).

I also want to control a joint for panning a camera on each of these robots. But when I try to start the controller manager, it gives the error:

[INFO] [WallTime: 1442100763.719533] [0.533000] Loading controller: camera_position_controller
[ERROR] [1442100763.811078289, 0.621000000]: Could not find parameter robot_description on parameter server
[ERROR] [1442100763.811171897, 0.621000000]: Failed to parse urdf file
[ERROR] [1442100763.811233707, 0.621000000]: Failed to initialize the controller
[ERROR] [1442100763.811282445, 0.621000000]: Initializing controller 'camera_position_controller' failed

The .yaml file for controller params.

  # Publish all joint states -----------------------------------
  joint_state_controller:
    type: joint_state_controller/JointStateController
    publish_rate: 10  

  # Position Controllers ---------------------------------------
  camera_position_controller:
    type: effort_controllers/JointPositionController
    joint: camera_joint
    pid: {p: 100.0, i: 0.01, d: 10.0}

The launch file:

<!-- these are the arguments you can pass this launch file, for example paused:=true -->

<!-- We resume the logic in empty_world.launch, changing only the name of 
    the world to be launched -->
<include file="$(find gazebo_ros)/launch/empty_world.launch">
    <arg name="world_name" value="$(find mrp_p3dx_gazebo)/worlds/mrp_p3dx.world" />
    <arg name="debug" value="$(arg debug)" />
    <arg name="gui" value="$(arg gui)" />
    <arg name="paused" value="$(arg paused)" />
    <arg name="use_sim_time" value="$(arg use_sim_time)" />
    <arg name="headless" value="$(arg headless)" />
</include>

<!-- BEGIN ROBOT 1-->
<group ns="robot1">
    <!-- <param name="tf_prefix" value="robot1" />  -->

    <!-- Load joint controller configurations from YAML file to parameter server -->
    <rosparam file="$(find mrp_p3dx_control)/config/mrp_p3dx.yaml" command="load"
        ns="/robot1" /> 

    <param name="robot_description"
    command="$(find xacro)/xacro.py '$(find mrp_p3dx_description)/urdf/robot1.xacro'" />

    <node name="urdf_spawner" pkg="gazebo_ros" type="spawn_model"
        respawn="false" output="screen" args="-urdf -x 5.5 -y 8 -z 0 -model robot1 -param robot_description" />

    <node pkg="robot_state_publisher" type="state_publisher" name="robot_state_publisher">
           <!-- <remap from="robot_description" to="robot_description" /> -->
          <param name="publish_frequency" type="double" value="30.0"/>
          <param name="tf_prefix" type="string" value="robot1"/>
    </node>

    <!-- load the controllers -->
    <node name="controller_spawner" pkg="controller_manager" type="spawner"
        respawn="false" ns="/robot1" output="screen" args="camera_position_controller joint_state_controller">
    </node>  

    <param name="publish_frequency" type="double" value="30.0"/>

</group>

<!-- BEGIN ROBOT 2-->
<group ns="robot2">
    <!-- <param name="tf_prefix" value="robot2" /> -->
    <param name="robot_description"
    command="$(find xacro)/xacro.py '$(find mrp_p3dx_description)/urdf/robot2.xacro'" />

    <node name="urdf_spawner" pkg="gazebo_ros" type="spawn_model"
        respawn="false" output="screen" args="-urdf -x 5 -y 5 -z 0 -model robot2
        -param robot_description" />

     <node pkg="robot_state_publisher" type="state_publisher" name="robot_state_publisher">
          <!-- <remap from="robot_description" to="robot_description" /> -->
          <param name="publish_frequency" type="double" value="30.0"/>
          <param name="tf_prefix" type="string" value="robot2"/>
    </node>

    <param name="publish_frequency" type="double" value="30.0"/>

</group>

<node pkg="tf" type="static_transform_publisher" name="base_to_odom_r1" 
 args="0.0 -0.0 0.0 0.0 0.0 0.0 map robot1/odom 200" />

<node pkg="tf" type="static_transform_publisher" name="base_to_odom_r2" 
 args="0.0  0.0 0.0 0.0 0.0 0.0 map robot2/odom 200" />

The gazeboroscontrol plugin in robot1.gazebo file

  <!-- ros_control plugin -->
  <gazebo>
    <plugin name="gazebo_ros_control" filename="libgazebo_ros_control.so">
        <robotParam>/robot1/robot_description</robotParam>
        <robotNamespace>/robot1</robotNamespace>
    </plugin>
  </gazebo>

This problem was talked about in some discussions and some work has been done. But I still get the same problem.

https://github.com/ros-simulation/gazebo\_ros\_pkgs/issues/112 https://github.com/ros-controls/ros_controllers/issues/19

I should also mention that the controller_manager detects the robot_description if its not in the namespace (i.e., /robot_description) and I am able to control the camera. But doing that will not help me in a multi-robot simulation where different robots have different robot_descriptions.