Question

Hi, I observe strange behavior in Gazebo when I'm trying to spawn many objects.

I created this xacro file for the object:

<?xml version="1.0"?>

<robot xmlns:xacro="http://www.ros.org/wiki/xacro" name="box_obstacle">
   <xacro:arg name="row" default="0"/>
   <xacro:arg name="col" default="0"/>
   <xacro:arg name="width" default="1"/>
   <xacro:arg name="height" default="1"/>

  <link name="obstacle" type="fixed">
    <inertial>
      <origin xyz="$(arg row) $(arg col) 0.5" />
      <mass value="1.0" />
      <inertia  ixx="0.0" ixy="0.0"  ixz="0.0"  iyy="0.0"  iyz="0.0"  izz="0.0" />
    </inertial>
    <visual>
      <origin xyz="$(arg row) $(arg col) 0.5"/>
      <geometry>
        <box size="$(arg width) $(arg height) 1" />
      </geometry>
    </visual>
    <collision>
      <origin xyz="$(arg row) $(arg col) 0.5"/>
      <geometry>
        <box size="$(arg width) $(arg height) 1" />
      </geometry>
    </collision>
  </link>
  <gazebo reference="obstacle">
    <static>true</static>
    <material>Gazebo/Black</material>
  </gazebo>

</robot>

and my launch file looks like this:

 <launch>
     <arg name="world" default="$(find my_package)/worlds/empty.world"/>

      <!-- We resume the logic in empty_world.launch, changing only the name of the world to be launched -->
      <include file="$(find gazebo_ros)/launch/empty_world.launch">
          <arg name="world_name" value="$(arg world)"/>
      </include>

     <param command="$(find xacro)/xacro.py $(find my_package)/objects/obstacle.urdf.xacro row:=6.5 col:=4.0 width:=3 height:=6" name="obstacle_0" />
     <node args="-urdf -param obstacle_0 -model obstacle_0" name="spawn_obstacle_0" output="screen" pkg="gazebo_ros" respawn="false" type="spawn_model" />
     <param command="$(find xacro)/xacro.py $(find my_package)/objects/obstacle.urdf.xacro row:=4.5 col:=4.0 width:=1 height:=2" name="obstacle_1" />
     <node args="-urdf -param obstacle_1 -model obstacle_1" name="spawn_obstacle_1" output="screen" pkg="gazebo_ros" respawn="false" type="spawn_model" />
     <param command="$(find xacro)/xacro.py $(find my_package)/objects/obstacle.urdf.xacro row:=-4.5 col:=-9.0 width:=9 height:=2" name="obstacle_2" />
     <node args="-urdf -param obstacle_2 -model obstacle_2" name="spawn_obstacle_2" output="screen" pkg="gazebo_ros" respawn="false" type="spawn_model" />
</launch>

This works fine with few "obstacles", but when I try about 10 (instead of 3 here) the simulator doing unexpected things (I'm trying to attach images but >5 points are needed :(, the linkes below will be valid only for 1 week).

 <launch>
     <arg name="world" default="$(find my_package)/worlds/empty.world"/>

      <!-- We resume the logic in empty_world.launch, changing only the name of the world to be launched -->
      <include file="$(find gazebo_ros)/launch/empty_world.launch">
          <arg name="world_name" value="$(arg world)"/>
      </include>

     <param command="$(find xacro)/xacro.py $(find my_package)/objects/obstacle.urdf.xacro row:=6.5 col:=4.0 width:=3 height:=6" name="obstacle_0" />
     <node args="-urdf -param obstacle_0 -model obstacle_0" name="spawn_obstacle_0" output="screen" pkg="gazebo_ros" respawn="false" type="spawn_model" />
     <param command="$(find xacro)/xacro.py $(find my_package)/objects/obstacle.urdf.xacro row:=4.5 col:=4.0 width:=1 height:=2" name="obstacle_1" />
     <node args="-urdf -param obstacle_1 -model obstacle_1" name="spawn_obstacle_1" output="screen" pkg="gazebo_ros" respawn="false" type="spawn_model" />
     <param command="$(find xacro)/xacro.py $(find my_package)/objects/obstacle.urdf.xacro row:=-4.5 col:=-9.0 width:=9 height:=2" name="obstacle_2" />
     <node args="-urdf -param obstacle_2 -model obstacle_2" name="spawn_obstacle_2" output="screen" pkg="gazebo_ros" respawn="false" type="spawn_model" />
    <param command="$(find xacro)/xacro.py $(find my_package)/objects/obstacle.urdf.xacro row:=-5.0 col:=-7.5 width:=2 height:=1" name="obstacle_3" />
    <node args="-urdf -param obstacle_3 -model obstacle_3" name="spawn_obstacle_3" output="screen" pkg="gazebo_ros" respawn="false" type="spawn_model" />
    <param command="$(find xacro)/xacro.py $(find my_package)/objects/obstacle.urdf.xacro row:=-2.0 col:=-1.5 width:=16 height:=1" name="obstacle_4" />
    <node args="-urdf -param obstacle_4 -model obstacle_4" name="spawn_obstacle_4" output="screen" pkg="gazebo_ros" respawn="false" type="spawn_model" />
    <param command="$(find xacro)/xacro.py $(find my_package)/objects/obstacle.urdf.xacro row:=-6.0 col:=-0.5 width:=4 height:=1" name="obstacle_5" />
    <node args="-urdf -param obstacle_5 -model obstacle_5" name="spawn_obstacle_5" output="screen" pkg="gazebo_ros" respawn="false" type="spawn_model" />
    <param command="$(find xacro)/xacro.py $(find my_package)/objects/obstacle.urdf.xacro row:=-0.5 col:=0.5 width:=19 height:=1" name="obstacle_6" />
    <node args="-urdf -param obstacle_6 -model obstacle_6" name="spawn_obstacle_6" output="screen" pkg="gazebo_ros" respawn="false" type="spawn_model" />
    <param command="$(find xacro)/xacro.py $(find my_package)/objects/obstacle.urdf.xacro row:=-2.5 col:=1.5 width:=1 height:=1" name="obstacle_7" />
    <node args="-urdf -param obstacle_7 -model obstacle_7" name="spawn_obstacle_7" output="screen" pkg="gazebo_ros" respawn="false" type="spawn_model" />
    <param command="$(find xacro)/xacro.py $(find my_package)/objects/obstacle.urdf.xacro row:=-0.5 col:=-5.0 width:=5 height:=4" name="obstacle_8" />
    <node args="-urdf -param obstacle_8 -model obstacle_8" name="spawn_obstacle_8" output="screen" pkg="gazebo_ros" respawn="false" type="spawn_model" />
    <param command="$(find xacro)/xacro.py $(find my_package)/objects/obstacle.urdf.xacro row:=0.0 col:=8.5 width:=20 height:=1" name="obstacle_9" />
    <node args="-urdf -param obstacle_9 -model obstacle_9" name="spawn_obstacle_9" output="screen" pkg="gazebo_ros" respawn="false" type="spawn_model" />
 </launch>

Is there a way to fix this? How can I tell the pyhsics engine to ignore these obstacles. They should be static and fixed to the ground.

Screen snapshots:

10 objects: http://uploadpie.com/7egqg http://uploadpie.com/hlGOO http://uploadpie.com/Xrlak

3 objects: http://uploadpie.com/Za3Bb http://uploadpie.com/FmSjl http://uploadpie.com/QlgJO

Thanks a lot

Asked by sefi_roee on 2016-04-16 12:34:23 UTC

Answer 1

There is a static tag for models : http://sdformat.org/spec?ver=1.6&elem=model

You can try to add the following lines to your urdf file (inside the robot tags) :

Update :

<gazebo>
    <static>true</static>
</gazebo>

<gazebo reference="obstacle">
    <material>Gazebo/Black</material>
</gazebo>

Asked by F.Brosseau on 2016-04-18 02:08:30 UTC

Comments

Thanks. As you can see, I already have similar line in my .xacro file

<gazebo reference="obstacle"> <static>true</static> <material>Gazebo/Black</material> </gazebo>

Do you think there is a difference between "1" and "true"?

Asked by sefi_roee on 2016-04-18 02:26:40 UTC

Sorry I didn't saw these lines. Can you check in Gazebo GUI that your models are really static ?

Asked by F.Brosseau on 2016-04-18 02:51:08 UTC

NP. In the Gazebo GUI i can see that the "static" attribute of the model is checked, but the models are still being affected by the physics. (For example, when i put two model on top of each other, I can see the gravity and other forces moving both the models).

Asked by sefi_roee on 2016-04-18 03:10:44 UTC

I use also gazebo with static = true and I have no problem. I also had 0

Asked by F.Brosseau on 2016-04-18 04:47:46 UTC

Hi, Tnx. I tried gravity=0, objects now flying around :( Did you see the pics i attached? Is this happening to you too?

Asked by sefi_roee on 2016-04-19 22:05:27 UTC

I saw the pics but I didn't had this problem. Maybe you can try to add a fixed joint between your flying objects and the world. Maybe you can have more help on this forum : http://answers.gazebosim.org/questions/

Asked by F.Brosseau on 2016-04-20 01:51:37 UTC

Could you please give me pic of the objects in your environment? Tnx a lot

Asked by sefi_roee on 2016-04-20 02:15:55 UTC

I used your code and I saw obstacle 4,6 and 9 "shaking". In your obstacle.urdf.xacro file, I changed <gazebo reference="obstacle"> to <gazebo> and there is no problem anymore

Answer updated

Asked by F.Brosseau on 2016-04-22 03:34:39 UTC

Bless you my friend. Finally it's working :)

Asked by sefi_roee on 2016-04-22 04:08:32 UTC

Error spawning many urdf's in Gazebo

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