onebot.urdf.xacro

onebot.urdf.xacro

<?xml version="1.0"?>
<robot  xmlns:xacro="http://ros.org/wiki/xacro"
        name="onebot" >

    <xacro:include filename="$(find onebot_description)/urdf/caster.urdf.xacro" />
    <xacro:include filename="$(find onebot_description)/urdf/wheel.urdf.xacro" />
   
    <xacro:arg name="mesh_enabled" default="true" />
    <xacro:arg name="robot_namespace" default="/"/> 
        
    <link   name = "base_link">
        <inertial>
            <origin xyz="-0.108 0 -0.02579" rpy="0 0 0"/>
            <mass value="3.978"/>
            <inertia ixx="0.021858680" ixy="0.0" ixz="0.010020353"
                    iyy="0.078572349" iyz="-0.0"
                    izz="0.091971324"/>
        </inertial>
        <visual>
            <xacro:if value="$(arg mesh_enabled)">
                <origin xyz="0 0 0" rpy="0 0 0" />
                <geometry>
                    <mesh filename="package://onebot_description/meshes/base_link.dae" />
                </geometry>
            </xacro:if>
            <xacro:unless value="$(arg mesh_enabled)">
                <origin xyz="-0.125 0 -0.01" rpy="0 0 0" />
                <geometry>
                    <box size="0.25 0.25 0.02" />
                </geometry>
                <material name="Blue" />    
            </xacro:unless>
        </visual>
        <collision>
            <origin xyz="-0.125 0 -0.01" rpy="0 0 0" />
            <geometry>
                <box size="0.25 0.25 0.02" />
            </geometry>
        </collision>
    </link>

    <link   name =  "base_footprint"/>
        
    <joint name = "base_joint"  type = "fixed">
        <parent link="base_footprint"/>
        <child link="base_link"/>
        <origin xyz="0.0 0.0 0.09188" rpy="0 0 0" />
        <axis xyz="0 1 0" rpy="0 0 0" />
    </joint>

    <xacro:caster caster_prefix="rear" parent_link="base_link" >
        <origin xyz="-0.20 0.0 -0.02533" rpy="0 0 0" />
    </xacro:caster>

    <xacro:wheel wheel_prefix="left" parent_link="base_link" >
        <origin xyz="-0.04 0.14 -0.045" rpy="0 0 0" />
    </xacro:wheel>

    <xacro:wheel wheel_prefix="right" parent_link="base_link" >
        <origin xyz="-0.04 -0.14 -0.045" rpy="0 0 0" />
    </xacro:wheel>

    <gazebo>
        <plugin name="gazebo_ros_control" filename="libgazebo_ros_control.so">
        <robotNamespace>$(arg robot_namespace)</robotNamespace>
        <legacyModeNS>true</legacyModeNS>
        </plugin>
    </gazebo>

</robot>

In line 5 and 6 I have included the caster file and the wheel file which included the xacro macros of caster and wheel. In line 8 I have defined a xacro argument which can be used for conditional formatting of the URDF file. Starting from line 10 I have defined the base_link.

The inertial tag of the base_link is filled using the mass properties data from the solidworks part.
Then the xacro arg is used inside the visual tag of base_link. If meshes are enabled, the collada file is used as the geometry otherwise a box of the given size is used. The same is used under the collision tag.

Then the base_footprint is defined which is a pseudo link. This is basically used to improve the visualization in Rviz (To lift up the robot to the ground plane) . A fixed joint is used to join the base_footprint with the base_link. The distance which has been used in the joint tag is the distance from the ground to the origin of the base_link.

Then the xacro macros are used. First the caster is instantiated and the expected arguments are given. Also the wheels are instantiated with the wheel prefix being left and right.

In line 62, gazebo ros control plugin is attached. This enables the usage of ROS controllers with the URDF model.