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Spherical Joint in URDF

asked 2018-10-02 09:45:32 -0600

CodeMade gravatar image

I have the following URDF. I striped out the meshes for this post. Does anyone know how to make the shapes that are on the x y and z axis move like a spherical/ball joint? If you use this URDF and launch in rviz you will see shapes representing x,y, and z axis. If you move them their anchor point is at the base.

<robot name="mira">

<material name="blue">
    <color rgba="0 0 0.8 1"/>
</material>
<material name="red">
    <color rgba="0.8 0 0 1"/>
</material>
<material name="green">
    <color rgba="0 0.8 0 1"/>
</material>
<material name="gray">
    <color rgba="0.9 0.9 0.9 1"/>
</material>


<!-- * * * Link Definitions * * * -->
<link name="base_link">
    <visual>
        <origin rpy="1.54 0 0" xyz="0 0 0.13"/>
        <geometry>

        </geometry>
        <material name="gray"/>
    </visual>
</link>



<link name="roll_M1_link">

    <visual>
        <origin rpy="0 0 0" xyz="0 0 0.125"/>
        <geometry>
            <cylinder length="0.005" radius="0.01"/>
        </geometry>
        <material name="red"/>
    </visual>
</link>
<!-- This is for color and physical properties in Gazebo, color won't work with the material tag in gazebo
only for URDF coloring -->
<gazebo reference="roll_M1_link">
    <kp>1000.0</kp>
    <kd>10.0</kd>
    <mu1>10.0</mu1>
    <mu2>10.0</mu2>
    <material>Gazebo/Red</material>
</gazebo>

<joint name="roll_joint" type="revolute">
    <parent link="base_link"/>
    <child link="roll_M1_link"/>
    <origin xyz="0.0 0 0.0" rpy="0 0 0"/>
    <limit lower="-0.4" upper="0.3" effort="0.1" velocity="0.005"/>
    <axis xyz="1 0 0"/>
</joint>


<link name="pitch_M2_link">

    <visual>
        <origin rpy="0 0 0" xyz="0.125 0 0"/>
        <geometry>
            <cylinder length="0.005" radius="0.01"/>
        </geometry>
        <material name="green"/>
    </visual>
</link>

<!-- This is for color and physical properties in Gazebo, color won't work with the material tag in gazebo
only for URDF coloring -->
<gazebo reference="pitch_M2_link">
    <kp>1000.0</kp>
    <kd>10.0</kd>
    <mu1>10.0</mu1>
    <mu2>10.0</mu2>
    <material>Gazebo/Green</material>
</gazebo>

<joint name="pitch_joint" type="revolute">
    <parent link="roll_M1_link"/>
    <child link="pitch_M2_link"/>
    <origin xyz="0 0 0" rpy="0 -1.5708 0"/>
    <limit lower="-0.22" upper="0.22" effort="0.1" velocity="0.005"/>
    <axis xyz="0 1 0"/>
</joint>



<link name="yaw_M3_link">

    <visual>
        <origin rpy="0 0 0" xyz="0 0 0.125"/>
        <geometry>
            <cylinder length="0.005" radius="0.01"/>
        </geometry>
        <material name="blue"/>
    </visual>
</link>

<!-- This is for color and physical properties in Gazebo, color won't work with the material tag in gazebo
only for URDF coloring -->
<gazebo reference="yaw_M3_link">
    <kp>1000.0</kp>
    <kd>10.0</kd>
    <mu1>10.0</mu1>
    <mu2>10.0</mu2>
    <material>Gazebo/Blue</material>
</gazebo>


<joint name="yaw_joint" type="continuous">
    <parent link="pitch_M2_link"/>
    <child link="yaw_M3_link"/>
    <origin xyz="0.01 0 0" rpy="0 1.5708 0"/>
    <limit effort="0.1" velocity="0.01"/>
    <axis xyz="0 0 1"/>
</joint>


<link name="head_link">
    <visual>
        <origin rpy="1.54 0 0" xyz="0 0 0.122"/>
        <geometry>

        </geometry>
        <material name="gray ...
(more)
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1 Answer

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answered 2018-10-02 16:00:13 -0600

David Lu gravatar image

The unsatisfying answer is that there is no native way to represent a ball joint other than similar to what you have, by breaking it into multiple joints.

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Comments

Those joints don’t move like a ball joint though. They move from a point below. How do I set the center of rotation in the center of the joints I have created?

CodeMade gravatar imageCodeMade ( 2018-10-02 16:07:12 -0600 )edit

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Asked: 2018-10-02 09:45:32 -0600

Seen: 204 times

Last updated: Oct 02 '18