Dear all,

I am fairly new to ROS and Gazebo.

I am using ros-kinetic and gazebo7.3 on Ubuntu 16.04. I have been following this tutorial (http://www.generationrobots.com/blog/en/2015/02/robotic-simulation-scenarios-with-gazebo-and-ros/) and have adapted it slightly for my own vehicle (4 wheels instead of 2, skid drive plugin instead of diff drive).

I receive errors when running roslaunch on my own project, and I get the same errors when using the same command on the project provided at the above link. I assume that means that I am missing something in ros or Gazebo.

Running:

roslaunch jaguar4x4gazebo jaguar4x4world.launch

gives the following errors (repeated for each joint and trans):

[ERROR] [1472045218.311147687, 0.142000000]: No valid hardware interface element found in joint 'leftbackwheel_hinge'.

[ERROR] [1472045218.311359894, 0.142000000]: Failed to load joints for transmission 'leftbacktrans'.

Also:

[ERROR] [1472045218.646822285, 0.365000000]: Exception thrown while initializing controller leftfrontWheeleffortcontroller. Could not find resource 'leftfrontwheelhinge' in 'hardwareinterface::EffortJointInterface'. [ERROR] [1472045218.646923303, 0.366000000]: Initializing controller 'leftfrontWheeleffortcontroller' failed [ERROR] [WallTime: 1472045219.647578] [1.363000] Failed to load leftfrontWheeleffortcontroller [INFO] [WallTime: 1472045219.647938] [1.363000] Loading controller: leftbackwheeleffortcontroller [ERROR] [1472045219.650602709, 1.366000000]: Could not load controller 'leftbackwheeleffortcontroller' because the type was not specified. Did you load the controller configuration on the parameter server (namespace: '/jaguar4x4/leftbackwheeleffortcontroller')? [ERROR] [WallTime: 1472045220.651591] [2.366000] Failed to load leftbackwheeleffortcontroller

This error is repeated for each of the 4 wheels.

I have seen similar error messages posted on this site, the solutions don’t seem to fix mine.

(1). http://answers.gazebosim.org/question/6654/gazeboos-x-109-no-valid-hardware-interface-element-found-in-joint/

I already use the hardwareInterface tags

(2). I have already installed ros_control

EDIT -------------------------------------------------------------------

I think maybe there is an issue with the way that I have created my joints and the use of the hardwareInterface tags.

In my macros.xacro file I create my joints and link the transmission separately (I repeat this twice for the front and back wheels):

   <joint name="${lr}_front_wheel_hinge" type="continuous">
      <parent link="chassis"/>
      <child link="${lr}_front_wheel"/>
      <origin xyz="${+wheelPos-chassisLength+2*wheelRadius} ${tY*wheelWidth/2+tY*chassisWidth/2} ${wheelRadius}" rpy="0 0 0" />
      <axis xyz="0 1 0" rpy="0 0 0" />
      <limit effort="100" velocity="100"/>
      <joint_properties damping="0.0" friction="0.0"/>
    </joint>

  <transmission name="${lr}_front_trans">
    <type>transmission_interface/SimpleTransmission</type>
    <joint name="${lr}_front_wheel_hinge" /> 
    <actuator name="${lr}_front_Motor"> 
      <hardwareInterface>EffortJointInterface</hardwareInterface>
      <mechanicalReduction>10</mechanicalReduction>
    </actuator> 
  </transmission>

Doing it this way gives the errors mentioned above, but my model in Gazebo appears.

If I try to merge both of these blocks so that there is just one joint tag wrapped by the transmission tags then I get the following error and my model does not appear in Gazebo:

[ERROR] [1473672367.041892175]: Failed to find root link: Two root links found: [footprint] and [leftbackwheel]

I don't understand why I get this error because I have a joint between my chassis base link and the world in my Jaguar4x4.xacro file :

 <link name="footprint" /> 

 <joint name="base_joint" type="fixed">
   <parent link="footprint"/>
   <child link="chassis"/>
 </joint>

I now get a number of errors when trying to combine the joint and transmission blocks, so I imagine that this is not the best way to go?

Edit 2 -------------------------------------------------------------------------

Here is my jaguar4x4control/config/jaguar4x4control.yaml file:

jaguar4x4:
  # Publish all joint states -----------------------------------
  joint_state_controller:
    type: joint_state_controller/JointStateController
    publish_rate: 50  


  # Effort Controllers ---------------------------------------
  leftfrontWheel_effort_controller:
    type: effort_controllers/JointEffortController
    joint: left_front_wheel_hinge
    pid: {p: 100.0, i: 0.1, d: 10.0}
  leftbackWheel_effort_controller:
    type: effort_controllers/JointEffortController
    joint: left_back_wheel_hinge
    pid: {p: 100.0, i: 0.1, d: 10.0}
  rightfrontWheel_effort_controller:
    type: effort_controllers/JointEffortController
    joint: right_front_wheel_hinge
    pid: {p: 100.0, i: 0.1, d: 10.0}
  rightbackWheel_effort_controller:
    type: effort_controllers/JointEffortController
    joint: right_back_wheel_hinge
    pid: {p: 100.0, i: 0.1, d: 10.0}