Used the description.launch and the wheel_static_transf.launch files to simplify the launch file.

launch/spawn_pioneer3.launch

@@ -8,18 +8,14 @@
   <arg name="yaw" default="0.0"/>
 
   <group ns="$(arg name)">
-  
-    <param name="robot_description"
-          command="$(find xacro)/xacro --inorder '$(find iri_pioneer3_description)/urdf/$(arg model).xacro' name:=$(arg name)" />
 
-    <node pkg="robot_state_publisher" type="state_publisher" name="state_publisher">
-      <param name="tf_prefix" type="string" value="$(arg name)"/>
-      <param name="publish_frequency" type="double" value="20.0"/>
-    </node>
-    
-    <node pkg="joint_state_publisher" type="joint_state_publisher" name="joint_state_publisher">
-    </node>
+    <include file="$(find iri_pioneer3_description)/launch/description.launch">
+      <arg name="node_name" value="$(arg name)"/>
+      <arg name="model" value="$(arg model)"/>
+    </include>
 
+    <include file="$(find iri_pioneer3_description)/launch/wheel_static_transform.launch"/>
+  
     <node name="spawn_urdf" pkg="gazebo_ros" type="spawn_model" args="-param robot_description -urdf -model $(arg name) -x $(arg x) -y $(arg y) -z 0 -R 0 -P 0 -Y $(arg yaw)" />
   
   </group>