[BREAKING CHANGE] Use robot_description topic instead of `~/robot_d…

…escription` and update docs regarding this (ros-controls#1410)

* Use `robot_description` instead of `~/robot_description` topic
   Using robot_description by default instead will work for most people out of the box while also working correctly with different descriptions in different namespaces when using remaps.
  Nowadays, the parameter is deprecated and will be removed.

---------

Co-authored-by: Sai Kishor Kothakota <[email protected]>
Co-authored-by: Dr. Denis <[email protected]>

controller_manager/doc/userdoc.rst

@@ -70,10 +70,6 @@ hardware_components_initial_state.unconfigured (optional; list<string>; default:
 hardware_components_initial_state.inactive (optional; list<string>; default: empty)
   Defines which hardware components will be configured immediately when controller manager is started.
 
-robot_description (mandatory; string)
-  String with the URDF string as robot description.
-  This is usually result of the parsed description files by ``xacro`` command.
-
 update_rate (mandatory; integer)
   The frequency of controller manager's real-time update loop.
   This loop reads states from hardware, updates controller and writes commands to hardware.
@@ -83,6 +79,55 @@ update_rate (mandatory; integer)
   Name of a plugin exported using ``pluginlib`` for a controller.
   This is a class from which controller's instance with name "``controller_name``" is created.
 
+Subscribers
+-----------
+
+robot_description (std_msgs/msg/String)
+  The URDF string as robot description.
+  This is usually published by the ``robot_state_publisher`` node.
+
+Handling Multiple Controller Managers
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+When dealing with multiple controller managers, you have two options for managing different robot descriptions:
+
+1. **Using Namespaces:** You can place both the ``robot_state_publisher`` and the ``controller_manager`` nodes into the same namespace.
+
+.. code-block:: python
+
+   control_node = Node(
+       package="controller_manager",
+       executable="ros2_control_node",
+       parameters=[robot_controllers],
+       output="both",
+       namespace="rrbot",
+   )
+   robot_state_pub_node = Node(
+       package="robot_state_publisher",
+       executable="robot_state_publisher",
+       output="both",
+       parameters=[robot_description],
+       namespace="rrbot",
+   )
+
+2. **Using Remappings:** You can use remappings to handle different robot descriptions. This involves relaying topics using the ``remappings`` tag, allowing you to specify custom topics for each controller manager.
+
+.. code-block:: python
+
+   control_node = Node(
+       package="controller_manager",
+       executable="ros2_control_node",
+       parameters=[robot_controllers],
+       output="both",
+       remappings=[('robot_description', '/rrbot/robot_description')]
+   )
+   robot_state_pub_node = Node(
+       package="robot_state_publisher",
+       executable="robot_state_publisher",
+       output="both",
+       parameters=[robot_description],
+       namespace="rrbot",
+   )
 
 Helper scripts
 --------------

controller_manager/src/controller_manager.cpp

@@ -284,7 +284,7 @@ ControllerManager::ControllerManager(
     RCLCPP_WARN(
       get_logger(),
       "[Deprecated] Passing the robot description parameter directly to the control_manager node "
-      "is deprecated. Use '~/robot_description' topic from 'robot_state_publisher' instead.");
+      "is deprecated. Use the 'robot_description' topic from 'robot_state_publisher' instead.");
     init_resource_manager(robot_description_);
     init_services();
   }
@@ -329,7 +329,7 @@ void ControllerManager::subscribe_to_robot_description_topic()
   // set QoS to transient local to get messages that have already been published
   // (if robot state publisher starts before controller manager)
   robot_description_subscription_ = create_subscription<std_msgs::msg::String>(
-    "~/robot_description", rclcpp::QoS(1).transient_local(),
+    "robot_description", rclcpp::QoS(1).transient_local(),
     std::bind(&ControllerManager::robot_description_callback, this, std::placeholders::_1));
   RCLCPP_INFO(
     get_logger(), "Subscribing to '%s' topic for robot description.",