invisible mesh in gazebo

edit

Some shots in the dark:

1. Do you by any chance have an Intel GMA integrated graphics chipset? I know that RViz has problems displaying STL meshes on Intel chipsets, maybe Gazebo does too. Things to try:

   • test your URDF on a computer with a dedicated graphics card (NVidia works well usually)
   • convert your STL file to DAE using meshlab
   • try if RViz can display your model (run gazebo and RViz, then enable "Robot model" visualization in RViz)

2. I'm not sure whether Gazebo displays the "visual" or the "collision" model. Try also putting the mesh into the "collision" tag.

3. This should be a no-brainer, but still: can Gazebo find your mesh file at the specified location? There should be an error message on the console if it can't.

Edit: I've just tested your URDF file, and it looks like your minimal example was a little too minimal :-). You need at least one extra link for Gazebo to display anything. The following works for me:

<robot name="TX60L">

  <link name="base_link" >
    <inertial>
      <origin xyz="0 0 0" /> 
      <mass value="1.0" />
      <inertia  ixx="0.001" ixy="0.0"  ixz="0.0"  iyy="0.001"  iyz="0.0"  izz="0.001" />
    </inertial>

    <visual>
      <origin xyz="0 0 0" rpy="0 0 0" />
      <geometry>
        <mesh filename="package://learning_urdf/meshes/tx60l/bt.stl" />
      </geometry>             
    </visual>

    <collision>
      <origin xyz="0 0 0" rpy="0 0 0" />
      <geometry>
        <mesh filename="package://learning_urdf/meshes/tx60l/bt.stl" />
      </geometry>             
    </collision>
  </link>

  <joint name="dummy_joint" type="fixed">
    <parent link="base_link" />
    <child link="dummy_link" />
    <origin xyz="2.0 0 0" rpy="0 0 0" />
  </joint>

  <link name="dummy_link" >
    <inertial>
      <origin xyz="2 0 0" /> 
      <mass value="1.0" />
      <inertia  ixx="0.001" ixy="0.0"  ixz="0.0"  iyy="0.001"  iyz="0.0"  izz="0.001" />
    </inertial>

    <visual>
      <origin xyz="0 0 0"/>
      <geometry>
        <box size="0.4 0.4 0.4" />
      </geometry>
    </visual>

    <collision>
      <origin xyz="0 0 0"/>
      <geometry>
        <box size="0.4 0.4 0.4" />
      </geometry>
    </collision>
  </link>
</robot>

If you need more help, please also upload your STL file somewhere (I tested with one of my own STL meshes).