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why my robot arm rotate by itself?

asked 2011-08-29 02:28:35 -0500

shenhaobin gravatar image

updated 2011-08-29 20:27:43 -0500

hi,everyone. I went to simulate my robot arm in gazebo.Here is my urdf file.


<robot name="jixiebi1">
  <link name="base_link">
    <visual>
      <geometry>
        <box size="1.5 1 0.2"/>
      </geometry>
      <origin rpy="0 0 0" xyz="0 0 0.1"/>
      <material name="blue">
        <color rgba="0 0 .8 1"/>
      </material>
    </visual>
    <collision>
      <geometry>
        <box size="1.5 1 0.2"/>
      </geometry>
      <origin rpy="0 0 0" xyz="0 0 0.1"/>
    </collision>
    <inertial>
      <mass value="200"/>
      <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>
    </inertial>
  </link>
  <joint name="base_link-arm1-11" type="fixed">
    <parent link="base_link"/>
    <child link="arm1-11"/>
    <origin rpy="0 0 0" xyz="0 0 0.2"/>
  </joint>
    <link name="arm1-11">
        <visual>
            <geometry>
                <mesh filename="arm - arm1.STL"/>
            </geometry>
            <origin rpy="0 0 0" xyz="0 0 0"/>
            <material name="arm1-11_color">
                <color rgba="0.752941 0.752941 0.752941 1"/>
            </material>
        </visual>
        <collision>
            <geometry>
                <mesh filename="arm - arm1.STL"/>
            </geometry>
            <origin rpy="0 0 0" xyz="0 0 0"/>
        </collision>
        <inertial>
            <mass value="1.04075"/>
            <inertia ixx="0.004368" ixy="-0.00001" ixz="0.000002" iyy="0.004367" iyz="-0.000001" izz="0.002456"/>
            <origin rpy="0 0 0" xyz="0.000393 -0.000373 -0.074418"/>
        </inertial>
    </link>
    <joint name="arm1-11-arm2-11" type="continuous">
        <limit effort="1000.0" lower="-3.1415926" upper="3.1415926" velocity="0.5"/>
        <dynamics damping="1000.0" friction="1000.0"/>
        <parent link="arm1-11"/>
        <child link="arm2-11"/>
        <origin rpy="0 0 0" xyz="0 0 0.172"/>
        <axis xyz="0 0 1"/>
    </joint>
    <link name="arm2-11">
        <visual>
            <geometry>
                <mesh filename="arm - arm2.STL"/>
            </geometry>
            <origin rpy="0 0 0" xyz="0 0 0.0"/>
            <material name="arm2-11_color">
                <color rgba="0.752941 0.752941 0.752941 1"/>
            </material>
        </visual>
        <collision>
            <geometry>
                <mesh filename="arm - arm2.STL"/>
            </geometry>
            <origin rpy="0 0 0" xyz="0 0 0.0"/>
        </collision>
        <inertial>
            <mass value="1.26789"/>
            <inertia ixx="0.003947" ixy="-0.000001" ixz="-0.000617" iyy="0.006723" iyz="-0.000004" izz="0.005568"/>
            <origin rpy="0 0 0" xyz="-0.100667 0.000085 -0.013708"/>
        </inertial>
    </link>
    <gazebo reference="base_link">
        <material>Gazebo/GrassFloor</material>
        <turnGravityOff>false</turnGravityOff>
        <selfCollide>true</selfCollide>
    </gazebo>
    <gazebo reference="arm1-11">
        <mu1>100</mu1>
        <mu2>100</mu2>
        <material>Gazebo/White</material>
        <turnGravityOff>true</turnGravityOff>
        <selfCollide>true</selfCollide>
    </gazebo>
    <gazebo reference="arm2-11">
        <mu1>100</mu1>
        <mu2>100</mu2>
        <material>Gazebo/White</material>
        <turnGravityOff>true</turnGravityOff>
        <selfCollide>true</selfCollide>
    </gazebo>
</robot>

When I ran the urdf file, I found the arm2-11 link turn around arm1-11 link. I went to know is there any way to make the arm2-11 link static in begin running.

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2 Answers

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answered 2011-08-29 20:42:18 -0500

hsu gravatar image

updated 2011-08-29 20:43:55 -0500

It's possible the dynamic damping is way too large. Try setting it to 0

    <dynamics damping="0.0" friction="0.0"/>

Given that the gravity effects are turned off, the arms should not move when you start up simulation.

Also, try setting <selfCollide> tags to false in case your collision geometries are in collision with each other

    <selfCollide>false</selfCollide>

Friction has no effect at this time.

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yes,it works. But now it has another problems. When I give the arm2-11 link a force, three links rotate in mid-air. I think this maybe cause by the gravity disable. So how to deal with the problem?
shenhaobin gravatar imageshenhaobin ( 2011-08-30 15:03:22 -0500 )edit
1
shenhaobin, your new problem is different from your initial problem, so can you post it in a new question?
Wim gravatar imageWim ( 2011-09-01 04:07:52 -0500 )edit
2

answered 2011-08-29 03:27:10 -0500

Lorenz gravatar image

I'm not sure if I understand your question correctly but since you use a joint of type continuous between the links arm1-11 and arm2-11, arm2-11 will rotate around arm1-11.

When no controller is running which is the case when you start up gazebo, no forces are applied to the arm but gravity which might cause the arm link to rotate. You can find some information on how to specify controllers here. To control the arm, you can also use the ros_controller_manager plugin. You can find some information on that here, though I couldn't find a tutorial on that.

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hi, thanks for your replying! I have reviewed the web site which you linked above, but I still don't know how to solve this problem. My idea is very simple. I just went to arm2-11 rotate around arm1-11 when I give it a force.
shenhaobin gravatar imageshenhaobin ( 2011-08-29 20:09:39 -0500 )edit
But they must keep static in first running just like there is a friction between arm1-11 and arm2-11. So I went to know is there any label to achieve this effect. But the site on how to use controllers label is too simply. My email is hb.shen@siat.ac.cn. if necessary, I can send my stl files to you.
shenhaobin gravatar imageshenhaobin ( 2011-08-29 20:15:45 -0500 )edit

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Asked: 2011-08-29 02:28:35 -0500

Seen: 1,084 times

Last updated: Aug 29 '11