what does the revolute joint's effort limit be zero mean?

asked 2016-10-17 09:35:15 -0500

yin
58 ●12 ●17 ●21

 <joint name="joint_1" type="revolute">
  <origin rpy="0 0 0" xyz="0 0 0"/>
  <parent link="base_link"/>
  <child link="link_1"/>
  <limit effort="0" lower="-2.87979" upper="2.87979" velocity="4.36332"/>
  <axis xyz="0 0 1"/>
  <dynamics damping="0.0" friction="0.0"/>
</joint>

hello, from above can see the effort limit is set to zero, I want to know what does this mean? another question: now I am using an abb industrial arm in ROS, when start it's gazebo launch the arm will not fall down. I have some puzzle about this, because the arm link has it's own mass. Thank you for help!

answered 2016-10-17 11:21:51 -0500

gvdhoorn
86574 ●283 ●1432 ●1054 http://cor.tudelft.nl/

A limit of 0 basically means no limit.

For ROS-Industrial robot support packages, a 0-limit is used to either indicate that there is no limit, or that the manufacturer hasn't disclosed it.

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Oh, thank you, could you also give me some tips about the second question? I have one of my own robot arm urdf that was exported from solidworks, but when simulated in gazebo, the arm link would fall down because of it's gravity. Is it something wrong like the mass value in my urdf model?

yin ( 2016-10-17 20:52:27 -0500 )edit

In general it's not a good idea to ask two questions in a single ROS Answers question, even if they are related.

I'm not a Gazebo expert, might be that you have gravity disabled on the links in question, or that the mass is not correct, or something else.

gvdhoorn ( 2016-10-18 06:49:04 -0500 )edit

<gazebo reference="${prefix}base_link"> <material>Gazebo/Orange</material> <turngravityoff>true</turngravityoff> </gazebo>

ok, thank you very much! you are right, the link gravity is turned off in xacro file, I just find it.

yin ( 2016-10-18 07:31:51 -0500 )edit

Hi, gvdhoorn, I find that when the effort limit was set to zero, the joint would not move, I have test it by change it's urdf. But in abb_irb120_moveit_config pkg the moveit_planning_execution_gazebo.launch can move it, I don't know why.

yin ( 2016-10-18 08:31:38 -0500 )edit

(again: please don't treat ROS Answers like a regular forum. We have a rather strict one question per Q/A convention here).

You've probably configured your gazebo xacro/pkg to use an effort controller. The ABB pkgs are using position controllers for exactly this reason.

gvdhoorn ( 2016-10-18 09:42:29 -0500 )edit

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