[ros-users] Only the fixed link shows up in gazebo (cturtle)

John Hsu johnhsu at willowgarage.com
Wed Jul 21 02:12:27 UTC 2010

Hi Grace,

I've answered inline.

On Tue, Jul 20, 2010 at 3:43 PM, Yeon Grace Lee <yeongrace.lee at gmail.com>wrote:

> Hi All,
> I am trying to spawn my person_urdf in gazebo but instead of the entire
> human model, only one of the links is showing up. It seems that the other
> links were not spawned (they are neither in the sky nor the ground). Lower
> torso, which is the link that shows up in gazebo, is neither the fixed link
> nor the root link. Attached is the urdf file that i am spawning in gazebo.

Any child(ren) of "virtual" links (links without inertia/collision/visual
elements) are ignored in gazebo simulation (with the exception of the
"world" link, or the inertial frame).  There's an open
ticket<https://code.ros.org/trac/ros-pkg/ticket/3524>for this feature.

> Also, guessing from the previous urdf files in our USC repository, is it
> necessary to have a "world" joint whose parent is world and child is the
> root link? I wasn't sure if this was something I should take into
> consideration while working with urdf/gazebo in cturtle.

As of cturtle, we do not require world-joint anymore.  Instead, if you
attach your model to the inertial frame by specifying a joint with world as
the parent link, you will need to declare a virtual link for the world:
<link name="world"/>

My last question is, in order to manipulate several joints at once (i.e.
> shoulder moves while hip rotates, etc), is it necessary to divide up the
> link which is currently in one urdf file into separate urdf files as your
> PR2 model has done?

No.  The division and use of xacro macros simply allows us to reuse various
components of the robot urdf.  In the end, the PR2 robot urdf is described
by one single file/string, e.g.:

rosrun xacro xacro.py `rospack find pr2_description`/robots/pr2.urdf.xacro >

hope this helps,

> Thank you in advance,
> Grace L.
> p.s. below is the snapshot of the terminal for spawning the urdf model in
> gazebo.
> yglee at yglee-laptop:~/cturtle_usc/stacks/interaction-ros-pkg/sandbox/person_urdf2$
> roslaunch person_urdf2 person_gazebo.launch
> ... logging to
> /home/yglee/.ros/log/29ed66c2-944f-11df-afd2-00236c960005/roslaunch-yglee-laptop-8830.log
> Checking log directory for disk usage. This may take awhile.
> Press Ctrl-C to interrupt
> Done checking log file disk usage. Usage is <1GB.
> started roslaunch server http://yglee-laptop:51427/
> ========
>  * /use_sim_time
>  * /robot_description
>   /
>     gazebo (gazebo/gazebo)
>     human (gazebo_tools/gazebo_model)
> ROS_MASTER_URI=http://yglee-laptop:11311/
> core service [/rosout] found
> process[gazebo-1]: started with pid [8850]
> process[human-2]: started with pid [8851]
> Gazebo multi-robot simulator, version 0.10.0
> Part of the Player/Stage Project [http://playerstage.sourceforge.net].
> Copyright (C) 2003 Nate Koenig, Andrew Howard, and contributors.
> Released under the GNU General Public License.
> directory [/tmp/gazebo-yglee-0] already exists (previous crash?)
> but the owner gazebo server (pid=8743) is not running.
> deleting the old information of the directory [/tmp/gazebo-yglee-0]
> Gazebo successfully initialized
> [human-2] process has finished cleanly.
> log file:
> /home/yglee/.ros/log/29ed66c2-944f-11df-afd2-00236c960005/human-2*.log
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