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Difference between <dynamics damping="0.7" friction="100.0" /> and <mu1>1</mu1>

asked 2011-12-17 08:52:34 -0500

maruchi gravatar image

updated 2012-01-09 16:22:33 -0500

Wim gravatar image

Hi,

Could anyone give me some explanation the difference between dynamics damping, and mu1, mu2 in the urdf ?

As I understand it, mu1 and mu2 are tangential friction forces applied between body and surface, so that the tangential friction force applied to the body as the body weight when mu=1.

<dynamics damping="0.7" friction="100.0"/> is the damping force which is proportional to the velocity of the moving body.

What should I do in the urdf to applying the damping force which is proportional to the velocity in the simple sliding box? Below is the sliding box urdf code:

<robot name="sliding_box"
       xmlns:body="http://playerstage.sourceforge.net/gazebo/xmlschema/#body"
       xmlns:controller="http://playerstage.sourceforge.net/gazebo/xmlschema/#controller"
       xmlns:interface="http://playerstage.sourceforge.net/gazebo/xmlschema/#interface" >

  <link name="base_link">
    <inertial>
      <mass value="1"/>
      <origin xyz="0 0 0"/>
      <inertia ixx="0.05" ixy="0" ixz="0" iyy="0.05" iyz="0" izz="0.05"/>
    </inertial>
    <visual>
      <origin rpy="0 0 0" xyz="0 0 0.0"/>
      <geometry>
        <box size="1.0 1.0 1.0"/>
      </geometry>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0 0 0.0"/>
      <geometry>
        <box size="1.0 1.0 1.0"/>
      </geometry>
    </collision>
  </link>

  <gazebo reference="base_link">
    <mu1>0</mu1>
    <mu2>0</mu2>
    <fdir1 value = "1 0 0"/>
 <dynamics damping="0.7" friction="100.0" />
    <material>Gazebo/Black</material>
    <turnGravityOff>false</turnGravityOff>
  </gazebo>

  <gazebo>
        <controller:gazebo_ros_force name="box_force_controller" plugin="libgazebo_ros_force.so">
         <alwaysOn>true</alwaysOn>
         <updateRate>15.0</updateRate>
         <topicName>box_force</topicName>
         <bodyName>base_link</bodyName>
        </controller:gazebo_ros_force>
  <controller:gazebo_ros_p3d name="p3d_base_controller" plugin="libgazebo_ros_p3d.so">
    <alwaysOn>true</alwaysOn>
    <updateRate>15.0</updateRate>
    <bodyName>base_link</bodyName>
    <topicName>base_pose_ground_truth</topicName>
    <gaussianNoise>0</gaussianNoise>
    <frameName>map</frameName>
    <xyzOffsets>0 0 0</xyzOffsets> 
    <rpyOffsets>0 0 0</rpyOffsets>
    <interface:position name="p3d_base_position"/>
  </controller:gazebo_ros_p3d>
  </gazebo>

</robot>
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2 Answers

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answered 2012-04-19 12:22:21 -0500

Wim gravatar image

updated 2014-11-14 18:44:41 -0500

130s gravatar image

The "dynamics" element is part of the URDF description, and applies to the damping and friction in a joint. See the URDF page for more details.

The "mu1" and "mu2" elements are part of a Gazebo description, and apply to the material properties of a body.

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Comments

2

The current link is http://wiki.ros.org/urdf/XML/joint (J needs to be lower case). http://gazebosim.org/tutorials?tut=ro... has more info on the gazebo surface friction.

lucasw gravatar image lucasw  ( 2014-11-14 17:24:30 -0500 )edit

+1 Link in the post updated

130s gravatar image 130s  ( 2014-11-14 19:12:58 -0500 )edit
-1

answered 2018-10-01 03:04:55 -0500

itfanr gravatar image

updated 2018-10-01 03:06:46 -0500

<dynamics> (optional)

An element specifying physical properties of the joint. These values are used to specify modeling properties of the joint, particularly useful for simulation. damping (optional, defaults to 0)

The physical damping value of the joint ($$\frac{N \cdot s}{m}$$ for prismatic joints, $$\frac{N \cdot m \cdot s}{rad}$$ for revolute joints).

friction (optional, defaults to 0)

The physical static friction value of the joint ($$N$$ for prismatic joints, $$N \cdot m$$ for revolute joints).

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You may want to update your answer because this site doesn't support LaTeX

jayess gravatar image jayess  ( 2018-10-01 14:12:22 -0500 )edit

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Asked: 2011-12-17 08:52:34 -0500

Seen: 10,093 times

Last updated: Oct 01 '18