ignition-gazebo sensors problem

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Hi,

I am trying out ignition-gazebo and tried migrating my own robot. i can see the robot in gazebo but when i type ign topic -l, nothing displays on my terminal. I am trying to add IMU to my imu link that i wrote myself. Strangely, when converting from urdf to sdf, the fixed links are all combined into base_link as visuals only..?

This is the sdf for my robot:

<?xml version="1.0" ?>
<sdf version='1.9'>
<world name="mobile_base_arm_world">
  <physics name="1ms" type="ignored">
      <max_step_size>0.001</max_step_size>
      <real_time_factor>1.0</real_time_factor>
  </physics>

  <plugin
      filename="libignition-gazebo-physics-system.so"
      name="ignition::gazebo::systems::Physics">
  </plugin>
  <plugin
      filename="libignition-gazebo-user-commands-system.so"
      name="ignition::gazebo::systems::UserCommands">
  </plugin>
  <plugin
      filename="libignition-gazebo-scene-broadcaster-system.so"
      name="ignition::gazebo::systems::SceneBroadcaster">
  </plugin>
  <plugin filename="ignition-gazebo-sensors-system"
          name="ignition::gazebo::systems::Sensors">
          <render_engine>ogre2</render_engine>
  </plugin>
  <plugin filename="ignition-gazebo-imu-system"
                name="ignition::gazebo::systems::Imu">
  </plugin>

  <gui fullscreen="0">

      <!-- 3D scene -->
    <plugin filename="GzScene3D" name="3D View">
      <ignition-gui>
      <title>3D View</title>
      <property type="bool" key="showTitleBar">false</property>
      <property type="string" key="state">docked</property>
      </ignition-gui>

      <engine>ogre2</engine>
      <scene>scene</scene>
      <ambient_light>0.4 0.4 0.4</ambient_light>
      <background_color>0.8 0.8 0.8</background_color>
    </plugin>

    <!-- World control -->
    <plugin filename="WorldControl" name="World control">
      <ignition-gui>
      <title>World control</title>
      <property type="bool" key="showTitleBar">false</property>
      <property type="bool" key="resizable">false</property>
      <property type="double" key="height">72</property>
      <property type="double" key="width">121</property>
      <property type="double" key="z">1</property>

      <property type="string" key="state">floating</property>
      <anchors target="3D View">
          <line own="left" target="left"/>
          <line own="bottom" target="bottom"/>
      </anchors>
      </ignition-gui>

      <play_pause>true</play_pause>
      <step>true</step>
      <start_paused>true</start_paused>
      <service>/world/mobile_base_arm_world/control</service>
      <stats_topic>/world/mobile_base_arm_world/stats</stats_topic>
    </plugin>

    <!-- World statistics -->
    <plugin filename="WorldStats" name="World stats">
      <ignition-gui>
      <title>World stats</title>
      <property type="bool" key="showTitleBar">false</property>
      <property type="bool" key="resizable">false</property>
      <property type="double" key="height">110</property>
      <property type="double" key="width">290</property>
      <property type="double" key="z">1</property>

      <property type="string" key="state">floating</property>
      <anchors target="3D View">
          <line own="right" target="right"/>
          <line own="bottom" target="bottom"/>
      </anchors>
      </ignition-gui>

      <sim_time>true</sim_time>
      <real_time>true</real_time>
      <real_time_factor>true</real_time_factor>
      <iterations>true</iterations>
      <topic>/world/mobile_base_arm_world/stats</topic>

    </plugin>
    <!-- Entity tree -->
    <plugin filename="EntityTree" name="Entity tree">
    </plugin>

    <!-- KeyPublisher plugin-->
    <plugin filename="KeyPublisher" name="Key Publisher"/>

  </gui>

  <light type="directional" name="sun">
    <cast_shadows>true</cast_shadows>
    <pose>0 0 10 0 0 0</pose>
    <diffuse>0.8 0.8 0.8 1</diffuse>
    <specular>0.2 0.2 0.2 1</specular>
    <attenuation>
      <range>1000</range>
      <constant>0.9</constant>
      <linear>0.01</linear>
      <quadratic>0.001</quadratic>
    </attenuation>
    <direction>-0.5 0.1 -0.9</direction>
  </light>


  <model name="ground_plane">
    <static>true</static>
    <link name="link">
      <collision name="collision">
      <geometry>
        <plane>
        <normal>0 0 1</normal>
        </plane>
      </geometry>
      </collision>
      <visual name="visual">
      <geometry>
        <plane>
        <normal>0 0 1</normal>
        <size>100 100</size>
        </plane>
      </geometry>
      <material>
        <ambient>0.8 ...