Joint State Publisher produces empty messages

edit

Hello,

This questions can be split into two:

The first one. I am currently using in my URDF in Gazebo a ROS_control controller to control the platform wheels (velocity and position interface) and I am wondering if there is a way to plot the PID values in order to see the performance. Since I do not have any /command/data and /state/process_value topics I cannot plot the behavior of the PIDs.

The second one is related to the first question. Since I do not have those topics I want now to plot the changes on the jointStates. Robot_state_publisher and joint_state_publisher are launched properly but when you read the joint state topic there are certain messages which appear to be empty, this follows a pattern because this empty message happens every 4 messages, the 5th one is the empty one:

header: 
  seq: 74
  stamp: 
    secs: 7
    nsecs: 400000000
  frame_id: ''
name: [front_right_wheel_steer_joint, front_right_wheel_joint, front_right_shock,
  front_left_wheel_steer_joint, front_left_wheel_joint, front_left_shock,
  back_right_wheel_steer_joint, back_right_wheel_joint, back_right_shock,
  back_left_wheel_steer_joint, back_left_wheel_joint, back_left_shock]
position: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
velocity: []
effort: []

Joint state publisher node is publishing at a rate of 50 and I thought that was the problem, but changes on that value will output the same behavior.

If someone can help me with this I will appreciate.

Thanks in advance.

Update:

Here is the launch file:

<?xml version="1.0"?>

<launch>

  <!-- these are the arguments you can pass this launch file, for example paused:=true -->
  <arg name="gui" default="true"/>
  <arg name="use_joint_state_publisher" default="false"/>
  <arg name="setup" default="setup_4"/> <!-- Different setups for the sensors -->
  <arg name="ultrasonic_on" default="1"/> <!-- Different setups for the sensors -->
  <arg name="zed_on" default="1"/> <!-- Different setups for the sensors -->

  <group ns="ares">

    <!-- Load the URDF into the ROS Parameter Server -->
    <param name="robot_description"
    command="$(find xacro)/xacro --inorder '$(find ares_description)/urdf/bus/ares.xacro' setup:=$(arg setup) 
    ultrasonic_on:=$(arg ultrasonic_on) zed_on:=$(arg zed_on)" />

    <!-- send fake joint values -->
    <node if="$(arg use_joint_state_publisher)" name="joint_state_publisher" pkg="joint_state_publisher" type="joint_state_publisher" output="screen"/>

    <!-- Combine joint values -->
    <node name="robot_state_publisher" pkg="robot_state_publisher" type="robot_state_publisher" output="screen"/>

    <!-- Display with rviz -->
    <node name="rviz" pkg="rviz" type="rviz" respawn="false" output="screen"/>

  </group>

</launch>

If you change the parameter use_joint_state_publisher to true the model is well defined in tf and visualize in rviz.