Use xacro:macro as parent & another xacro:macro as child for a xacro:macro

edit

Connect (continuous) front car wheel to a (revolute) axel to steer a single car wheel. Not looking to get fancy.

I do you call xacro's within each other to make more xacro's? I'm missing some simple logic and haven't found a solution.

Also using Humble on 22.04.

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

  <!-- Define robot constants -->
  <xacro:property name="base_width" value="0.073"/>
  <xacro:property name="base_length" value="0.142"/>
  <xacro:property name="base_height" value="0.024"/>

  <xacro:property name="wheel_radius" value="0.0135"/>
  <xacro:property name="wheel_width" value="0.011"/>
  <xacro:property name="wheel_ygap" value="0.00002"/>
  <xacro:property name="wheel_zoff" value="0.006"/>
  <xacro:property name="wheel_xoff" value="0.045"/>

  <!-- Robot Base -->
  <link name="base_link">
    <visual>
      <geometry>
        <box size="${base_length} ${base_width} ${base_height}"/>
      </geometry>
      <material name="Cyan">
        <color rgba="0 1.0 1.0 1.0"/>
      </material>
    </visual>
  </link>

  <!-- Robot Footprint -->
  <link name="base_footprint"/>

  <joint name="base_joint" type="fixed">
    <parent link="base_link"/>
    <child link="base_footprint"/>
    <origin xyz="0.0 0.0 ${-(wheel_radius+wheel_zoff)}" rpy="0 0 0"/>
  </joint>

<!-- Front Axles -->
<!-- Revolute to mimic steering for each front wheel. -->
  <xacro:macro name="fr_axle" params="prefix x_reflect y_reflect">
    <link name="${prefix}_link">
      <visual>
        <origin xyz="0 0 0" rpy="$0 0 0"/>
        <geometry>
            <cylinder radius="${wheel_radius}" length="${wheel_width}"/>
        </geometry>
        <material name="Gray">
          <color rgba="0.5 0.5 0.5 1.0"/>
        </material>
      </visual>
    </link>

    <joint name="${prefix}_joint" type="revolute">
      <parent link="base_link"/>
      <child link="${prefix}_link"/>
      <origin xyz="${x_reflect*wheel_xoff} ${y_reflect*(base_width/2+wheel_ygap)} ${-wheel_zoff}" rpy="0 0 0"/>
      <axis xyz="0 0 1"/>
      <limit lower="-0.575959" upper="0.575959" effort="12.2" velocity="2.0"/>
      <!-- Heads up that I haven't wrapped my head ^^ around effort and velocity ^^  -->
    </joint>
  </xacro:macro>

  <!-- Steering axles needed for front wheels -->
  <!-- I just want to connect each wheel to it's own axle because it seems like less trouble. -->
  <xacro:fr_axle prefix="axle_l" x_reflect="1" y_reflect="1" />
  <xacro:fr_axle prefix="axle_r" x_reflect="1" y_reflect="-1" />

<!-- Front wheels-->
<!-- Continuous spin to mimic front car wheels. -->
  <xacro:macro name="f_wheel" params="prefix x_reflect y_reflect">
    <link name="${prefix}_link">
      <visual>
        <origin xyz="0 0 0" rpy="${pi/2} 0 0"/>
        <geometry>
            <cylinder radius="${wheel_radius}" length="${wheel_width}"/>
        </geometry>
        <material name="Gray">
          <color rgba="0.5 0.5 0.5 1.0"/>
        </material>
      </visual>
    </link>

    <joint name="${prefix}_joint" type="continuous">
      <parent link="base_link"/>
      <child link="${prefix}_link"/>
      <origin xyz="${x_reflect*wheel_xoff} ${y_reflect*(base_width/2+wheel_ygap)} ${-wheel_zoff}" rpy="0 0 0"/>
      <axis xyz="0 1 ...