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Toggling contact of wheel

asked 2014-01-31 04:22:34 -0600

Dr_Oppenheimer gravatar image

I have created a model by using the URDF export plugin for SolidWorks and converted it into the SDF format. In Gazebo some joints start moving. The problem appears to be a toggling contact of the wheel with the ground. Please watch the youtube video to understand what I am refering to.

3 wheel robotic platform in gazebeo

The video is x10 times the normal speed, as the movement is very small. Unfortunately I cannot upload the SDF file in lack of Karma.

so here is a sniplet of the wheel

 <link name='rad'>
  <pose>0.0724995 0 -0.435 -1.57079 0 0</pose>

  <inertial>
    <pose>0 0 0 0 -0 0</pose>
    <mass>0.54391</mass>
    <inertia>
      <ixx>0.0034711</ixx>
      <ixy>0</ixy>
      <ixz>0</ixz>
      <iyy>0.0034739</iyy>
      <iyz>0</iyz>
      <izz>0.0061305</izz>
    </inertia>
  </inertial>

  <collision name='rad_collision'>
    <pose>0 0 0 0 -0 0</pose>
    <geometry>
    <cylinder>
        <radius>0.130</radius> 
        <length>0.09</length>
    </cylinder>
      <!-- <mesh>
        <scale>1 1 1</scale>
        <uri>file://rad.dae</uri>
      </mesh> -->
    </geometry>

<surface>
      <friction>
        <ode>
          <mu>10.0</mu>
          <mu2>10.0</mu2>
          <slip1>10</slip1>
          <slip2>10</slip2>
        </ode>
    <bullet>
    <friction>10.0</friction>
    <friction2>10.0</friction2>
    <fdir1>1 1 0</fdir1>
    <rolling_friction>1.0</rolling_friction>
    </bullet>
      </friction>

  <contact>
    <ode>
        <soft_cfm>0</soft_cfm>
        <soft_erp>0.1</soft_erp>
        <kp>1e+10</kp>      
        <kd>10</kd>
        <max_vel>0.01</max_vel>
        <min_depth>1</min_depth>
    </ode>
  </contact>
  </surface>

And thats the sniplet for the corresponding joint

 <joint name='Jrad' type='revolute'>
  <child>rad</child>
  <parent>gabel</parent>
  <axis>
    <xyz>0 1 0</xyz>
    <limit>
      <lower>-1e+16</lower>
      <upper>1e+16</upper>
    </limit>
    <dynamics>
    <damping>0.8</damping>
    <friction>0.0001</friction>
    </dynamics>
  </axis>
</joint>

I have tried different values for mu, friction friction etc. with limited success. Maybe someone sees the error in my approach.


The system i am working on:

OS: Ubuntu 3.8.0-35-generic #50~precise1-Ubuntu SMP Wed Dec 4 17:25:51 UTC 2013 x8664 x8664 x86_64 GNU/Linux

Gazebo: version 2.1.0

ROS: Furete

BR and thanks for any help in advance!

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1 Answer

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answered 2014-01-31 18:41:02 -0600

scpeters gravatar image

There are several parameters that can be adjusted to improve contact behavior. I apologize that this is not well-documented at the moment. Please take a look at the min_depth parameter in this change to the Polaris EV model.

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Comments

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Thanks for your answer! I have tried different parameters, with minor success. The most important parameters to really improve is the number of contacts, which I have reduced to 1. Also I have manually altered some parameters that the Solidworks plugin has created. I will create a simpler model with the inertial and mass values and try to pinpoint the problem further.Whats interesting is the fact, that if gravity is turned of the model would float away. This is a symptom of the model bouncing.

Dr_Oppenheimer gravatar imageDr_Oppenheimer ( 2014-02-11 09:23:12 -0600 )edit
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Asked: 2014-01-31 04:22:34 -0600

Seen: 1,513 times

Last updated: Jan 31 '14