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My robot arm moves as soon as it's loaded in Gazebo

asked 2016-05-05 04:29:04 -0500

gabri89 gravatar image

updated 2016-05-05 09:55:53 -0500

Hi everyone,

I've loaded a robot arm in Gazebo. It's rappresented in urdf file and it appear correctly. I launch gazebo paused, but when I start the simulation the arm moves alone, without any applied force. It can be due by some contact (internal) force in the arm? Have you any suggests?

It seem that the arm goes to a new position, than it stays there.

Thank you!

Hi @nkoenig , and hi everyone.

I update my questions. I have an urdf directory, with the .xacro file. In this .xacro file I created link and joints eith this template:

<!-- ARM -->
<link name ="name_link">
  <origin xyz="-0.00543349 -0.04480023 0.01581062" rpy="0 0 0"/>
  <mass value="1.81745527"/>
  <inertia ixx="0.00571053"  ixy="0.00041083"  ixz="-0.00005130" iyy="0.01126908" iyz="-0.00003461" izz="0.01371197" />
  <origin xyz="0 0 0" rpy="0 0 0"/>
  <geometry name="name_link_visual">
    <mesh filename="package://my_directory/meshes/mesh_name.STL" scale="0.001 0.001 0.001" />
  <material name="material_name"/>
  <origin xyz="0 0 0" rpy="0 0 0"/>
  <geometry name="name_link_collision">
    <mesh filename="package://my_directory/meshes/simple/mesh_name.STL" scale="0.001 0.001 0.001" />


And joints:

<joint name="joint_name" type="revolute">
<parent link="link_name1"/>
<child link="link_name2"/>
<origin xyz="0.036 0.0 -0.15" rpy="0 0 0" />
<axis xyz="0 1 0" />
<limit velocity="6.283" effort="60" lower="${-170.0*toRad}" upper="${34.0*toRad}" />
<dynamics friction="100" damping="10.0"/>       

I used same meshes that are in meshes directory, and are .stl type. I tried to change joints friction and damping ( I increase them), and the behaviour change, but the motion of the arm remains. Do you think that this values can be the problem? I connect the arm with a fixed link, even if I connect them without contact, the arm begins to rotate. Can I modify something? Thank you.

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The movement can be caused by any number of things. Can you update your question detailing everything you have done to debug your model?

nkoenig gravatar imagenkoenig ( 2016-05-05 09:32:03 -0500 )edit

It seems that there is a force on some link/joint. I tried to add <selfcollide>false</selfcollide> but nothing changes. I can't understand what's the cause of the motion.

gabri89 gravatar imagegabri89 ( 2016-05-06 02:02:52 -0500 )edit

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answered 2016-05-12 05:14:01 -0500

gabri89 gravatar image

It was a stupid error: I set upper and lower limit to one joint, but it started out from this range. So Gazebo tried to bring the joint in the closer limit.

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Asked: 2016-05-05 04:29:04 -0500

Seen: 2,306 times

Last updated: May 12 '16