Wheel slippery, wrong direction and not straight

asked 2018-02-21 14:25:27 -0500

Boregard gravatar image

updated 2018-02-23 14:10:39 -0500

Hi,

created a differential drive robot with a ball caster. Tried to set mu1 and mu2 values of the wheels to values >1 and <1 for the caster. But the robot stands still and the wheels are slipping. Sometimes it moves slowly around the caster.

You may find the xacro files here: Robot definition

Thanks for your help and any ideas.

UPDATE: Tried to add a fixed joint with a link of a box with mass of 10. (idea was to get more weight on the wheels - just a stupid idea because of frustration :) ) -> nothing changed. Bot seems to be fixed around the caster and the wheels spin around and are slipping.

Anybody any advise?

UPDATE 2: I just recognized that the wheels are turning backwards when i use the i key in teleop. I changed the wheel separation parameter in the differencial drive plugin for gazebo. Robot now moves a little bit but really strange, it not moves straight forward ihr backward. It slips sidewise. See video. video

BR Marco

Update: Added content of xacro files:

hallrover_v2.xacro

<?xml version="1" ?>
<robot name="hallrover_v2" xmlns:xacro="http://www.ros.org/wiki/xacro">
  <xacro:property name="hallrover_body_width" value="0.20"/>
  <xacro:property name="hallrover_body_length" value="1.50"/>
  <xacro:property name="hallrover_body_heigth" value="0.10"/>
  <xacro:property name="hallrover_frame_heigth" value="0.05"/>
  <xacro:property name="hallrover_frame_width" value="1.34"/>
  <!-- - roller_length*2 + roller_body_space*2 + hallrover_body_width + hallrover_frame_thick*2 -->
  <xacro:property name="hallrover_frame_length" value="1.50"/>
  <xacro:property name="hallrover_frame_thick" value="0.05"/>
  <!-- hallrover_frame_height -->
  <xacro:property name="roller_length" value="0.50"/>
  <xacro:property name="roller_diam" value="0.25"/>
  <xacro:property name="roller_body_space" value="0.02"/>

  <!-- Import all Gazebo-customization elements, including Gazebo colors -->
  <xacro:include filename="$(find hallrover_v2)/urdf/hallrover_v2.gazebo"/>

 <xacro:include filename="$(find hallrover_v2)/urdf/makros.xacro"/>
 <gazebo>
   <material>Gazebo/White</material>
 </gazebo>

  <link name="base_footprint">
   <visual>
      <origin xyz="0 0 0" rpy="0 0 0" />
      <geometry>
        <box size="0.001 0.001 0.001" />
      </geometry>
    </visual>
  </link>
  <joint name="base_joint" type="fixed">
    <parent link="base_footprint"/>
    <child link="base_link"/>
   <origin xyz="0 0 ${roller_diam}" rpy="0 0 0" />
  </joint>

  <gazebo reference="base_footprint">
    <mu1 value="0.01"/>
    <mu2 value="0.01"/>
      <fdir1 value="1 1 0"/>
    <material>Gazebo/White</material>
  </gazebo>

  <link name="base_link">
    <visual>
      <geometry>
        <box size="${hallrover_body_width} ${hallrover_body_length} ${hallrover_body_heigth}"/>
      </geometry>
      <origin xyz="0 0 0"/>
      <material name="white">
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <geometry>
        <box size="${hallrover_body_width} ${hallrover_body_length} ${hallrover_body_heigth}"/>
       <!-- TODO change size to hallrover frame -->
      </geometry>
    </collision>
    <!-- <xacro:box_inertia m="10" x="${hallrover_body_width}" y="${hallrover_body_length}" z="${hallrover_body_heigth}"/>-->
    <xacro:box_inertial mass="2" x="${hallrover_body_width}" y="${hallrover_body_length}" z="${hallrover_body_heigth}"/>
  </link>
  <gazebo reference="base_link">
    <mu1 value="0.01"/>
    <mu2 value="0.01"/>
      <fdir1 value="1 1 0"/>
    <material>Gazebo/White</material>
  </gazebo>

 <xacro:include filename="$(find hallrover_v2)/urdf/hallrover_rollers_v2.xacro"/>

hallrover_rollers_v2.xacro

<?xml version="1" ?>
<robot xmlns:xacro="http://www.ros.org/wiki/xacro">

<link name="roller_left">
    <visual>
      <geometry>
        <cylinder length="${roller_length}" radius="${roller_diam /2}"/>
      </geometry>
      <origin rpy="0 ${pi/2} 0" xyz="0 0 0"/>
      <material name="black">
        <color rgba ...
(more)
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Comments

Could you please update your question with the contents of the xacro files? That way the question will be self-contained (should your files disappear from your Dropbox) and currently we have to download your files to view them.

jayess gravatar imagejayess ( 2018-02-21 15:02:36 -0500 )edit

Sure, thanks for advise. File content was added. BR Marco

Boregard gravatar imageBoregard ( 2018-02-21 15:10:45 -0500 )edit

@jayess@Boregard Did you find the fix for the robot moving backward rather than forward on "i" key press of teleop_twist_keyboard ?

the3kr gravatar imagethe3kr ( 2019-03-18 04:28:26 -0500 )edit