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Joints forming a closed loop of linkages - parallel linkages with SDF

asked 2013-07-12 19:01:00 -0500

FiliusFortunae gravatar image

Given the joints have a parent child relationship, is it possible to form loops? If not, are there workarounds? Does this vary between versions of Gazebo?

For context, I have been trying to adapt this urdf ( https://code.google.com/p/utexas-art-ros-pkg/source/browse/branches/sandbox/stacks/artexperimental/artgazebo_plugins/urdf/ackermann.urdf.xacro?r=1545 ) for Gazebo 1.5 that is included with the ROS-groovy. So far I have this ( https://gist.github.com/ftalex/5988718 )

Originally they used player and did this:

  <gazebo>
    <joint:hinge name="ackermann_right_bar_joint">
    <body1>ackermann_bar_link</body1>
    <body2>front_right_bar_link</body2>
    <anchor>ackermann_bar_link</anchor>
    <axis>0 0 1</axis>
    <anchorOffset>0 -0.45 0</anchorOffset>
  </joint:hinge>
</gazebo>

The original has a set of links and with joints so that they form parallel linkages, the two player joints close the loop on each side. I tried to just add joints to replace those in player:

<joint name='ackermann_left_bar_joint' type='revolute'>
        <parent>ackermann_bar_link</parent>
        <child>front_left_bar_link</child>
        <axis>
            <xyz>0.000000 0.000000 1.000000</xyz>
            <limit>
                <lower>-0.500000</lower>
                <upper>0.500000</upper>
                <effort>100.000000</effort>
                <velocity>10.000000</velocity>
            </limit>
            <dynamics/>
        </axis>
</joint>

This seems to do nothing and doesn't give any errors.

Eventually I want to use this with a plugin, but I am still learning about plugins.

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answered 2019-05-07 02:06:09 -0500

this post is marked as community wiki

This post is a wiki. Anyone with karma >75 is welcome to improve it.

the closed_loop_plugin can solve the issue that URDF not support Closed loop chains.

The URDF served the ROS, it has several notable shortcomings.one is it does not support closed loop chains. The SDF served the gazebo, support closed loop chains - this can be achieved by allowing two different joints to have the same child link but different parents

please refer to : http://wiki.ros.org/action/edit/Angel... or https://github.com/wojiaojiao/pegasus...

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Asked: 2013-07-12 19:01:00 -0500

Seen: 1,315 times

Last updated: Jul 12 '13