Possible to declare static object in urdf file?

asked 2012-03-09 04:54:40 -0500

Robert Krug
225 ●12 ●15 ●23

updated 2012-03-09 04:58:18 -0500

Hi,

I have a bunch of objects as urdf files which I use for simulation in Gazebo and visualization in Rviz. Now I would like some of them to be fixed in the environment. As stated here this is possible with Gazebo xml model files by putting following tag in the model.

<static>true</static>

However, simply putting the same tag in the gazebo extension of the urdf file like so:

<gazebo reference="my_object">
  <static>true</static>
</gazebo>

does not work, it simply gets ignored. I would like to use urdf files instead of Gazebo model xml's since urdf's can be easily visualized in Rviz by reading the description from the parameter server which does not seem to work for Gazebo model xml's. So, the question is whether there is a way to literally fix objects in their urdf file description opposed to simply making them very heavy.

Thanks, -Robert-

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answered 2012-03-11 19:07:40 -0500

hsu
5735 ●31 ●62 ●89

just add extension without the reference attribute to your model:

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

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Perfect, thank you!

Robert Krug ( 2012-03-12 01:48:24 -0500 )edit

Is it possible to make only a specific link static? I want only the base_link of my robot arm to be static (i.e. welded in place) while other links and joints can be actuated.

Rufus ( 2020-04-16 03:21:58 -0500 )edit

@Rufus, did you ever find a solution to this question? I am having the same issue.

matthewmarkey ( 2020-05-12 11:52:05 -0500 )edit

@matthewmarkey My conclusion was that I don't believe it is possible. The only way to achieve something similar is to explicitly specify in the urdf file a fixed joint between the world and the base_link

 <link name="world" />

 <joint name="world_joint" type="fixed">
    <parent link="world" />
    <child link = "base_link" />
    <origin xyz="0.0 0.0 0.1" rpy="0.0 0.0 0.0" />
 </joint>

I think it's unfortunate that changing where to spawn the arm (base link) requires changing the urdf. I would hope this can be done similar to spawning static objects in gazebo, just changing some parameters in the launch file.

Rufus ( 2020-05-15 02:29:36 -0500 )edit

Ok thank you @Rufus. When you change this in the URDF, should you also run the MSA again now that you have changed the URDF?

matthewmarkey ( 2020-05-18 04:03:10 -0500 )edit

@matthewmarkey what is MSA??

Rufus ( 2020-05-19 21:07:44 -0500 )edit

The Moveit Setup Assistant.

matthewmarkey ( 2020-05-20 02:12:49 -0500 )edit

I've never used Moveit Setup Assistant before so I'm not sure

Rufus ( 2020-05-20 03:53:38 -0500 )edit

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answered 2012-03-09 05:17:16 -0500

Kai Bublitz

357 ●12 ●12 ●22

Hi Robert,

you can fix a model to the world by adding the following lines to your URDF file:

<link name="world" />
<joint name="world_joint"  type="fixed">
    <origin xyz="2 0 1.5" rpy="0 0 0" />
    <parent link="world"/>
    <child link="your_models_root_link"/>
</joint>

Note that the object is fixed to the world at the position you specify in the joint, not the parameters you give to spawn_model.

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Thanks, that works but I'm still wondering if it's possible to set Gazebo`s static tag so that the physics engine doesn't try to recompute the fixed object's state at every iteration.

Robert Krug ( 2012-03-09 05:37:32 -0500 )edit

Hm for me it does not work... If I start the simulation my object (here: your_models_root_link) just falls down..... even with:

<gazebo reference="your_models_root_link">
    <static>true</static>
</gazebo>

Markus ( 2018-08-29 03:37:05 -0500 )edit

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