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Problem with two joints in arm

asked 2013-03-19 22:16:37 -0500

Jonathan Ruiz gravatar image

Hi!

I'm trying to build an arm to put on a quadrotor. I've written a urdf file to describe this arm. When I only have one joint everything works well, I can control this joint and everything is correct, but when I enable the second arm joint start to shake and I can't control it. It happens when I change joint "shoulder_y_arm_joint" from "fixed" to "revolute":

 <link name="arm_base_link">
      <inertial>
        <mass value="0.00001" />
        <origin xyz="0.0625 0.065 0.203" />
        <inertia ixx="0.0" ixy="0.0" ixz="0.0" iyy="0.0" iyz="0.0" izz="0.0" />
      </inertial>

      <visual>
        <origin xyz="0.0625 0.065 0.203" rpy="0.0 0.0 -2.3561925" />
        <geometry>
          <mesh filename="package://uav/Media/models/bonebraker/brazo0.dae"/>
        </geometry>
      </visual>

      <collision>
        <origin xyz="0.0625 0.065 0.203" rpy="0.0 0.0 -2.3561925" />
        <geometry>
          <mesh filename="package://uav/Media/models/bonebraker/brazo0.dae"/>
        </geometry>
      </collision>
    </link>
 <joint name="base_arm_joint" type="fixed">
        <parent link="base_link"/>
    <child link="arm_base_link"/>
  </joint>

<link name="shoulder_0">
      <inertial>
        <mass value="0.01" />
        <origin xyz="0.0 0.0 0.0" />
        <inertia ixx="0.01" ixy="0.0" ixz="0.0" iyy="0.01" iyz="0.0" izz="0.01" />
      </inertial>

      <visual>
        <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 -0.0" />
        <geometry>
          <mesh filename="package://uav/Media/models/bonebraker/brazo1.dae"/>
        </geometry>
      </visual>

      <collision>
        <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 -0.0" />
        <geometry>
          <sphere radius='0.0002'/>
          <!--<mesh filename="package://uav/Media/models/bonebraker/brazo1.dae"/>-->
        </geometry>
      </collision>
    </link>
 <joint name="shoulder_y_arm_joint" type="fixed">
    <axis xyz="0 0 1"/>
        <limit effort="1000" lower="-0.8726" upper="0.8726" velocity="0.001"/>
        <origin xyz="0.048 0.050 0.155" rpy="0.0 0.0 -2.3561925" />
        <parent link="arm_base_link"/>
    <child link="shoulder_0"/>
  </joint>

<link name="shoulder_1">
      <inertial>
        <mass value="0.00001" />
        <origin xyz="0.0 0.0 0.0" />
        <inertia ixx="0.00007" ixy="0.0" ixz="0.0" iyy="0.00007" iyz="0.0" izz="0.00007" />
      </inertial>

      <visual>
        <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 -0.0" />
        <geometry>
          <mesh filename="package://uav/Media/models/bonebraker/brazo2.dae"/>
        </geometry>
      </visual>

      <collision>
        <origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 -0.0" />
        <geometry>
           <sphere radius='0.0002'/>
        </geometry>
      </collision>
    </link>
 <joint name="shoulder_p_arm_joint" type="revolute">
    <axis xyz="0 1 0"/>
        <limit effort="0.1" lower="-3.14159" upper="1.0" velocity="0.001"/>
    <origin xyz="0.008 -0.00 -0.032" rpy="0.0 0.0 0.0" />
        <parent link="shoulder_0"/>
    <child link="shoulder_1"/>
  </joint>

Can you help me? Thank you in advance.

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Comments

I see nothing wrong in the URDF, I think you will have to describe your control structure a bit more, as that is probably the cause. Where are joint commands coming and going to? When you say it "shakes" do you mean the view in RVIZ or the physical robot?

fergs gravatar image fergs  ( 2013-03-19 23:10:26 -0500 )edit

I've resolved it now, I've turned gravity off in each link of arm and everything work well. Thanks!

Jonathan Ruiz gravatar image Jonathan Ruiz  ( 2013-03-20 00:57:07 -0500 )edit

1 Answer

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answered 2013-03-20 00:58:18 -0500

Jonathan Ruiz gravatar image

I've turned off gravity in each link and everything work well.

<gazebo reference="shoulder_0">
      <turnGravityOff>true</turnGravityOff>
</gazebo>
<gazebo reference="shoulder_1">
      <turnGravityOff>true</turnGravityOff>
</gazebo>

Thanks!

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Asked: 2013-03-19 22:16:37 -0500

Seen: 66 times

Last updated: Mar 20 '13