[Buoyancy Plugin] Possible bug

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Hi everybody,

I'm using Gazebo 6.6.0 with Ubuntu 14.04 and currently I'm experiencing strange behaviors with the buoyancy plugin shipped with this version.

The following minimal working example shows two sphere, of mass 1 kg, and the usage of the buoyancy plugin where I force the volume of these two sphere to be equal to their mass. Having fluid density equal to 1 should result having the two objects floating in the air, because in this case force_of_gravity == force_of_buoyancy. Unfortunately only the first sphere, l1, floats whereas the second one falls down.

<?xml version='1.0'?>
<sdf version='1.5'>
<model name="buoyancy_example">

  <!-- ================== link l1 ================== -->
  <link name="l1">

    <pose>0 0 1 0 0 0</pose>

    <inertial> <mass>1</mass> </inertial>

    <visual name='visual'>
      <geometry>
          <sphere> <radius>0.5</radius> </sphere>
      </geometry>
    </visual>

    <collision name='collision'>
      <geometry>
          <sphere> <radius>0.5</radius> </sphere>
      </geometry>
    </collision>

  </link>

  <!-- ================== link l2 ================== -->
  <link name="l2">

    <pose>2 0 1 0 0 0</pose>

    <inertial> <mass>1</mass> </inertial>

    <visual name='visual'>
      <geometry>
          <sphere> <radius>0.5</radius> </sphere>
      </geometry>
    </visual>

    <collision name='collision'>
      <geometry>
          <sphere> <radius>0.5</radius> </sphere>
      </geometry>
    </collision>

  </link>

  <!-- ================== buoyancy plugin ================== -->
  <plugin name="buoyancy" filename="libBuoyancyPlugin.so">

    <fluid_density>1</fluid_density>

    <link name="l1">
      <center_of_volume>0 0 0</center_of_volume>
      <volume>1</volume> <!-- volume == mass ==> object should float -->
    </link>

    <link name="l2">
      <center_of_volume>0 0 0</center_of_volume>
      <volume>1</volume> <!-- volume == mass ==> object should float -->
    </link>

  </plugin>

</model>
</sdf>

Based on my trials I believe that the problem is in this for statement here, which doesn't return the next link element within the plugin tag. Does anyone know how I can fix this bug and be able to use multiple "links" tags within this plugin?

Thanks,

Marco.