multi robots in uwsim

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Hello,

I tried to load two robots in environment, in order i put two <vehicle> tag with different position for them and also different topic for their navigation, but when i send data to topic of second robot, it is disappeared! is it possible at all to handle multi robots in uwsim ( i need to have many robots) and if it is possible how?! and also it is possible spawn robots inside of code or all thing must be handeled in XML file?

Thanks in advance.

it's my scenes:

blah blah blah ...
<vehicle>
    <name>visual</name>
    <file>data/scenes/r2d2_mm.urdf</file>
       <jointValues>
      <joint>0 </joint>
    </jointValues>
<position>
      <x> 0.2</x>
      <y> 0 </y>
      <z> 0.0 </z>
    </position>
    <orientation>
      <r>0</r>
      <p>0</p>
      <y>0</y>
    </orientation>

  </vehicle>

<vehicle>
    <name>visual1</name>
    <file>data/scenes/r2d2_mm.urdf</file>
       <jointValues>
      <joint>0 </joint>
    </jointValues>
<position>
      <x> 3</x>
      <y> 0 </y>
      <z> 0.0 </z>
    </position>
    <orientation>
      <r>0</r>
      <p>0</p>
      <y>0</y>
    </orientation>
  </vehicle>
.
.
.
    <rosInterfaces>
        <ROSOdomToPAT>
          <topic> /dataNavigator </topic>
          <vehicleName> visual </vehicleName>
        </ROSOdomToPAT>

        <ROSOdomToPAT>
          <topic> /dataNavigator1 </topic>
          <vehicleName> visual1 </vehicleName>
        </ROSOdomToPAT>
  </rosInterfaces>