Controller issue in Gazebo

edit

I am trying to load a controller (to control the speed of the 4 - joints) for the 4WD small robot I have created. I am following the tutorial on Gazebo wiki for the rrobot, but without success.

URDF FILE:

 <?xml version="1.0" ?>
<!-- =================================================================================== -->
<!-- |    This document was autogenerated by xacro from robot.xacro                    | -->
<!-- |    EDITING THIS FILE BY HAND IS NOT RECOMMENDED                                 | -->
<!-- =================================================================================== -->
<robot name="robot" xmlns:xacro="http://www.ros.org/wiki/xacro">
  <!--This URDF was automatically created by SolidWorks to URDF Exporter! Originally created by Stephen Brawner (brawner@gmail.com) 
     Commit Version: 1.5.1-0-g916b5db  Build Version: 1.5.7152.31018
     For more information, please see http://wiki.ros.org/sw_urdf_exporter -->
  <link name="base_link">
    <inertial>
      <origin rpy="0 0 0" xyz="0.00390777224516517 -0.032446267219719 0.184169550820421"/>
      <mass value="4.20121630268732"/>
      <inertia ixx="0.0149000386129946" ixy="-4.66831001352174E-09" ixz="5.23920338795194E-08" iyy="0.0234359493013497" iyz="0.000771538751024883" izz="0.0286744535302635"/>
    </inertial>
    <visual>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <geometry>
        <mesh filename="package://robot/meshes/base_link.STL"/>
      </geometry>
      <material name="">
        <color rgba="0.529411764705882 0.549019607843137 0.549019607843137 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <geometry>
        <mesh filename="package://robot/meshes/base_link.STL"/>
      </geometry>
    </collision>
  </link>
  <link name="FL">
    <inertial>
      <origin rpy="0 0 0" xyz="-5.55111512312578E-17 9.10729824887824E-18 -6.93889390390723E-18"/>
      <mass value="0.0615219544751675"/>
      <inertia ixx="5.54433425808419E-05" ixy="-1.45453466603006E-20" ixz="-1.00225538664655E-21" iyy="3.00921775305435E-05" iyz="2.309188417276E-21" izz="3.00921775305435E-05"/>
    </inertial>
    <visual>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <geometry>
        <mesh filename="package://robot/meshes/FL.STL"/>
      </geometry>
      <material name="">
        <color rgba="0.298039215686275 0.298039215686275 0.298039215686275 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <geometry>
        <mesh filename="package://robot/meshes/FL.STL"/>
      </geometry>
    </collision>
  </link>
  <joint name="FLJ" type="continuous">
    <origin rpy="1.5707963267949 0 0" xyz="-0.162088045105054 0.0440194465480433 -0.0035605397876617"/>
    <parent link="base_link"/>
    <child link="FL"/>
    <axis xyz="-1 0 0"/>
  </joint>
  <link name="FR">
    <inertial>
      <origin rpy="0 0 0" xyz="2.77555756156289E-17 -5.3776427755281E-17 3.46944695195361E-17"/>
      <mass value="0.0615219544751675"/>
      <inertia ixx="5.54433425808419E-05" ixy="-1.73616162087809E-20" ixz="-8.97406720914896E-21" iyy="3.00921775305435E-05" iyz="-2.24902265994014E-21" izz="3.00921775305435E-05"/>
    </inertial>
    <visual>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <geometry>
        <mesh filename="package://robot/meshes/FR.STL"/>
      </geometry>
      <material name="">
        <color rgba="0.298039215686275 0.298039215686275 0.298039215686275 1"/>
      </material>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <geometry>
        <mesh filename="package://robot/meshes/FR.STL"/>
      </geometry>
    </collision>
  </link>
  <joint name="FRJ" type="continuous">
    <origin rpy="1.5707963267949 0 ...