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Gazebo contact sensor added to a robot link in urdf file is not working as expected?

asked 2016-12-26 06:51:38 -0600

SP gravatar image

I have added a contact sensor to one of the finger links of a robot's gripper as follows:

 <link name="bh_finger_13_link">
    <inertial>
      <mass value="0.01"/>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <inertia ixx="1" ixy="0" ixz="0" iyy="1" iyz="0" izz="1" />
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0" />
      <geometry>
         <mesh file
  name="package://bh262_description/meshes/bhand/finger_tip.dae" />

   </geometry>
       <material name="Yellow" />
    </visual>
    <collision name="bh_finger_13_collision">
      <origin rpy="0 0 0" xyz="0.0 0.0 0.0"/>
      <geometry name="bh_finger_13_collision">
         <mesh filename="package://bh262_description/meshes/bhand/finger_tip.dae" />
      </geometry>
        <contact_coefficients kd="1.0" kp="1000.0" mu="0"/>
    </collision>
</link>

<gazebo reference="bh_finger_13_link">
   <sensor name='my_contact' type='contact'>
       <plugin name="my_plugin" filename="libcontact.so"/>
          <contact>
            <collision>bh_finger_13_link_collision</collision>
          </contact>
        <update_rate> 5 </update_rate>
        </sensor>
  </gazebo>

On lauching the urdf file, I am getting the gazebo topics /gazebo/default/wam/bh_finger_13_link/my_contact and /gazebo/default/wam/bh_finger_13_link/my_contact/contacts. However, on echoing these topics, I am not getting the collision data. In order to debug this issue, I have also added a contact sensor to a box model sdf, and made the finger link to touch this object. On echoing the topic associated with the contact sensor of the box model, I am getting the collision of the box with the finger link, but on echoing the topic associated with the finger link, I am not getting the same collision information. I am not able to figure out the reason behind this discrepancy. Any help is much appreciated.

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Did you find any solution ? I have exaclty the same issue: i'm able to have collision data from the sensor contact type in a world model but when i do it inside a robot then the collision is empty and on the dedicated topic I only have timestamps

TTDM gravatar imageTTDM ( 2017-01-18 09:06:52 -0600 )edit

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answered 2017-01-19 04:09:06 -0600

TTDM gravatar image

updated 2018-04-17 10:59:56 -0600

I found a work around !!!!!

Investigating what cause the issue, I found that there are issues parsing from urdf to sdf especially in the gazebo flag. Here is a link to a question in ros answer that does raise this issue : http://answers.gazebosim.org/question...

You can check on your own with editing an urdf from a xacro (rosrun xacro xacro.py -o robot.urdf robot.xacro) and then a sdf from an urdf (gz sdf -p robot.urdf > robot.sdf), you will see that the issues are with the collision flags, both the one inside the gazebo link and the one inside the link.

So their are 2 issues :

  • if you directly define a collision inside the <gazebo> flag, the urdf -> sdf parser does not allow it instead puts <collision>__default__</collision>
  • the 2nd one is that the collision name that you setup in the link part is modified but this modification does not occur in the gazebo collision : If i go back to your exemple, in the link, you will NOT create a "bh_finger_13_collision" collision but you will create a "bh_finger_13_collision_collision" but in the gazebo part you will still call "bh_finger_13_collision" which does not exists.

In order to make it work, this is awful but I believe the only way at the moment, you have to change the names of your collision according to this _collision add on only one side. For exemple you could still call your collision 'bh_finger_13_collision' in the link but then in the gazebo part, you need to call it "bh_finger_13_collision_collision"

TTDM,

Supplementary note : in complex projects, there are usually other adds to the name of the collision ( in my project, with my collision box being called "mav_collision_box", the final name on the sdf of my collision box is : shredder/base_link_fixed_joint_lump__mav_collision_box_collision and i have to call that exact name on inside the <gazebo> flag) so you should really generate your sdf using the two command lines i gave previously then manually search for the name of your collision and put it into the gazebo part (of your xacro file)

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Comments

Thank you! This is ugly, but fixed my issue. Mods - Can this be fixed?

dcconner gravatar imagedcconner ( 2017-03-07 19:15:47 -0600 )edit

Thank you! This also worked for me with ROS Indigo and Gazebo7.

jiriker gravatar imagejiriker ( 2017-03-07 23:51:36 -0600 )edit

I've already created an issue which describes the same behavior exactly one year ago, but it is still not assigned. You can find it here: https://bitbucket.org/osrf/sdformat/issues/113/parsing-from-urdf-to-sdf-does-not-handle. Follow the linked repository for details.

alextoind gravatar imagealextoind ( 2017-03-08 03:12:31 -0600 )edit

well the link in my answer is to your topic ;) What i did is basically explain how to go around it in a user point of vue which was not clearly stated in your post since your goal differ and was more to highligth the issue than to deal with it as a user ;)

TTDM gravatar imageTTDM ( 2017-03-09 02:10:22 -0600 )edit

Sure and thanks for that. I was just pointing out that I added the issue reference yesterday (I completely forgot to add it before).

alextoind gravatar imagealextoind ( 2017-03-09 02:16:01 -0600 )edit

I found that if you don't specify the collision name, you get something a lot nicer. E.g. if I specify the collision name (name="palm") I get: {link name}_fixed_joint_lump__palm_collision, but if I leave it empty I get: {link name}_collision. My recipe is then to simply leave the collision name of the link empty, and name the contact collision element as {link_name}_collision.

hamzamerzic gravatar imagehamzamerzic ( 2017-05-18 07:32:16 -0600 )edit

How did you load the edited sdf file?

Feynman gravatar imageFeynman ( 2018-01-25 10:13:26 -0600 )edit

HI, just saw your comment, you need to create the sdf file only to check it and then do the modifications on the xacro file ( but I guess that you solved it since January )

TTDM gravatar imageTTDM ( 2018-04-17 10:57:51 -0600 )edit
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Asked: 2016-12-26 06:51:38 -0600

Seen: 3,626 times

Last updated: Apr 17