CreateURDF.md

This is a Work in Progress document.

How to add a new robot

So in that case, the specific model and variation of the robot depends only in the robot.urdf.xacro that can be found in robots folder

To create a new robot that it's not defined in robotnik_description we will use the mobile base macro files. This macro files includes the body and wheels, all the basics of the robots, all the modifications are over this macro.

1. Start by including the macro files needed (robot base macro, sensors and all the needed structures).

<!-- Import all posible elements defined in the urdf.xacro files. All these elements are defined as macro:xacros -->

  <xacro:include
    filename="$(find robotnik_description)/urdf/bases/rbvogui/rbvogui_base.urdf.xacro" />
  <xacro:include
    filename="$(find robotnik_sensors)/urdf/all_sensors.urdf.xacro" />

2. Define arguments of the urdf.

  <!-- ARGUMENTS -->

  <xacro:arg name="namespace" default="robot"/>
  <xacro:arg name="prefix" default="robot_"/>
  <xacro:arg name="gazebo_ignition" default="false"/>

3. Call the macro of the robot base.

  <!-- Robot -->
  <xacro:rbvogui prefix="$(arg prefix)" hq="${hq}"/>

4. Call the macros of the sensors.

<!-- Sensors -->

  <xacro:sensor_sick_s300 prefix="rbkairos_front_laser" parent="rbkairos_base_link" prefix_topic="front_laser" gpu="true">
    <origin xyz="1.0 2.0 3.0" rpy="0 ${-pi} ${3/4*pi}" />
  </xacro:sensor_sick_s300>

5. Add arm if the robot has it.

  <xacro:include
    filename="$(find robotnik_description)/urdf/arms/ur_macro.urdf.xacro" />

  <!-- Arm -->
  <xacro:arm_ur
    ur_type="$(arg ur_type)"
    frame_prefix="$(arg prefix)arm_"
    parent="$(arg prefix)top_cover"
    gazebo_ignition="$(arg gazebo_ignition)">
    <origin
      xyz="0 0 0"
      rpy="0 0 0" />
  </xacro:arm_ur>

Robots

To understand the structure of the robots definition let's see an example, in this case the rbkairos.urdf.xacro.

First, it is included the macro file of the base robot (body + wheels) and the sensors macro that are in the package robotnik_sensors.

  <xacro:include
    filename="$(find robotnik_description)/urdf/bases/rbkairos/rbkairos_base.urdf.xacro" />
  <xacro:include
    filename="$(find robotnik_sensors)/urdf/all_sensors.urdf.xacro" />

Then, set default arguments to xacro:

  <!-- ARGUMENTS -->
  <xacro:arg name="namespace" default="robot" />
  <xacro:arg name="prefix" default="" />
  <xacro:arg name="gazebo_ignition" default="false" />

Next, the macro of the robot is called.

  <xacro:rbkairos
    prefix="$(arg prefix)"
    gazebo_ignition="$(arg gazebo_ignition)"
    namespace="$(arg namespace)" />

And finally the sensors are called, including the position declared in the properties.

  <!-- IMU -->
  <xacro:sensor_vectornav
    frame_prefix="$(arg prefix)imu_"
    parent="$(arg prefix)base_link"
    node_namespace="$(arg namespace)"
    gazebo_ignition="$(arg gazebo_ignition)">
    <origin
      xyz="0.127 -0.129 0.212"
      rpy="0 0 0" />
  </xacro:sensor_vectornav>

  <!-- LASERS -->
  <xacro:sensor_sick_s300
    frame_prefix="$(arg prefix)front_laser_"
    parent="$(arg prefix)base_link"
    node_namespace="$(arg namespace)"
    node_name="front_laser"
    gazebo_ignition="$(arg gazebo_ignition)">
    <origin
      xyz="0.2865 -0.20894 0.2973"
      rpy="0 ${-pi} ${3/4*pi}" />
  </xacro:sensor_sick_s300>

Let's see now the macro file definition.

MACROS

Moving to the macro file included in the previous robot file rbkairos_base.urdf.xacro.

As in the previous robot file, first it is included the robot body macro file and the wheels macro file.

  <xacro:include
    filename="$(find robotnik_description)/urdf/bodies/rbkairos/rbkairos_body.urdf.xacro" />
  <xacro:include
    filename="$(find robotnik_description)/urdf/wheels/mecanum_wheel/rbkairos_mecanum_wheel.urdf.xacro" />
  <xacro:include
    filename="$(find robotnik_description)/simulators/gazebo_ignition/rbkairos/rbkairos_control.urdf.xacro" />

Then, it is defined the properties of the position of the wheels.

  <!-- WHEELS PROPERTIES -->
  <xacro:property name="wheel_offset_x" value="0.21528" />
  <xacro:property name="wheel_offset_y" value="0.2590" />
  <xacro:property name="wheel_offset_z" value="0.0" />

And finally, the robot macro definition which includes calling the macro body (chassis + logos) and the wheels and control macros.

  <xacro:macro
    name="rbkairos"
    params="
      prefix:=robot_
      gazebo_ignition:=false
      namespace:=''
      ">
    <xacro:property
      name="hq"
      value="true" />
    <xacro:rbkairos_body prefix="${prefix}" />

    <!-- WHEELS -->
    <xacro:rbkairos_mecanum_wheel
      prefix="${prefix}front_right_"
      parent="${prefix}base_link"
      reflect="false"
      hq="true"
      gazebo_ignition="${gazebo_ignition}"
      xyz="${wheel_offset_x} -${wheel_offset_y} ${wheel_offset_z}" />
    <xacro:rbkairos_mecanum_wheel
      prefix="${prefix}front_left_"
      parent="${prefix}base_link"
      reflect="true"
      hq="true"
      gazebo_ignition="${gazebo_ignition}"
      xyz="${wheel_offset_x} ${wheel_offset_y} ${wheel_offset_z}" />
    <xacro:rbkairos_mecanum_wheel
      prefix="${prefix}back_left_"
      parent="${prefix}base_link"
      reflect="false"
      hq="true"
      gazebo_ignition="${gazebo_ignition}"
      xyz="-${wheel_offset_x} ${wheel_offset_y} ${wheel_offset_z}" />
    <xacro:rbkairos_mecanum_wheel
      prefix="${prefix}back_right_"
      parent="${prefix}base_link"
      reflect="true"
      hq="true"
      gazebo_ignition="${gazebo_ignition}"
      xyz="-${wheel_offset_x} -${wheel_offset_y} ${wheel_offset_z}" />

    <xacro:if value="$(arg gazebo_ignition)">
      <xacro:rbkairos_gz_ignition_control
        namespace="${namespace}"
        prefix="${prefix}" />
    </xacro:if>
  </xacro:macro>

Inner called macros:

• The macro body file includes the links and joints definition of the base_link, base_footprint, etc.

• The wheels macro file includes the links and joints of the mecanum wheel.