model.rsdf

<?xml version="1.0" ?>
<%
  # Vehicle with soft suspension
  # Consists of box chassis with 4 non-steerable wheels,
  # connected by prismatic joints to an intermediate body
  # SI units (length in meters)

  # Geometry
  chassis_dx   = 1.0
  chassis_dy   = 0.5
  chassis_dz   = 0.1
  susp_dx      = 0.05
  susp_dy      = susp_dx
  susp_dz      = susp_dx
  wheel_radius = 0.15
  wheel_width  = 0.08
  chassis_z0   = wheel_radius
  wheel_x0     = chassis_dx*0.5
  wheel_y0     = chassis_dy*0.5 + wheel_width*0.6

  wheel_locations = {
    "front_left"  => {:x0 => wheel_x0, :y0 => wheel_y0 },
    "front_right" => {:x0 => wheel_x0, :y0 => -wheel_y0 },
    "rear_left"   => {:x0 => -wheel_x0, :y0 => wheel_y0 },
    "rear_right"  => {:x0 => -wheel_x0, :y0 => -wheel_y0 },
  }

  # inertia
  chassis_mass = 10
  chassis_ixx  = chassis_mass/12.0 * (chassis_dy**2 + chassis_dz**2)
  chassis_iyy  = chassis_mass/12.0 * (chassis_dz**2 + chassis_dx**2)
  chassis_izz  = chassis_mass/12.0 * (chassis_dx**2 + chassis_dy**2)
  # chassis c.g. offset from center of box
  chassis_cgx  = chassis_dx*0.1
  chassis_cgy  = 0
  chassis_cgz  = 0
  # intermediate body (non-spinning unsprung inertia)
  susp_mass    = 0.5
  susp_ixx     = susp_mass/12.0 * (susp_dy**2 + susp_dz**2)
  susp_iyy     = susp_mass/12.0 * (susp_dz**2 + susp_dx**2)
  susp_izz     = susp_mass/12.0 * (susp_dx**2 + susp_dy**2)
  # wheel inertia
  wheel_mass   = 0.5
  wheel_ixx    = wheel_mass * (wheel_radius**2 / 4.0 + wheel_width**2 / 12.0)
  wheel_iyy    = wheel_mass * (wheel_radius**2 / 4.0 + wheel_width**2 / 12.0)
  wheel_izz    = wheel_mass/2.0 * wheel_radius**2
  # suspension stiffness, damping, and limits
  susp_travel    = 0.5 * wheel_radius
  susp_height    = 0.5
  susp_lower     = -susp_height * susp_travel
  susp_upper     = susp_lower + susp_travel
  susp_damping   = 100
  susp_stiffness = 2500
  susp_spring_center = 0.05
%>
<sdf version="1.5">
  <model name="cart_soft_suspension">
    <link name="chassis">
      <pose>0 0 <%= chassis_z0 %>  0 0 0</pose>
      <inertial>
        <pose><%= chassis_cgx %> <%= chassis_cgy %> <%= chassis_cgz %>  0 0 0</pose>
        <mass><%= chassis_mass %></mass>
        <inertia>
          <ixx><%= chassis_ixx %></ixx>
          <iyy><%= chassis_iyy %></iyy>
          <izz><%= chassis_izz %></izz>
          <ixy>0</ixy>
          <ixz>0</ixz>
          <iyz>0</iyz>
        </inertia>
      </inertial>
      <collision name="collision">
        <geometry>
          <box>
            <size><%= chassis_dx %> <%= chassis_dy %> <%= chassis_dz %></size>
          </box>
        </geometry>
      </collision>
      <visual name="visual">
        <geometry>
          <box>
            <size><%= chassis_dx %> <%= chassis_dy %> <%= chassis_dz %></size>
          </box>
        </geometry>
        <material>
          <script>
            <uri>file://media/materials/scripts/gazebo.material</uri>
            <name>Gazebo/Grey</name>
          </script>
        </material>
      </visual>
    </link>
    <%
      wheel_locations.keys.each do |k|
        x0 = wheel_locations[k][:x0]
        y0 = wheel_locations[k][:y0]
    %>
    <%= "<link name=" + '"susp_' + k + '">' %>
      <pose><%= x0 %> <%= y0 %> <%= wheel_radius %>  0 0 0</pose>
      <inertial>
        <mass><%= susp_mass %></mass>
        <inertia>
          <ixx><%= susp_ixx %></ixx>
          <iyy><%= susp_iyy %></iyy>
          <izz><%= susp_izz %></izz>
          <ixy>0</ixy>
          <ixz>0</ixz>
          <iyz>0</iyz>
        </inertia>
      </inertial>
      <collision name="collision">
        <geometry>
          <box>
            <size><%= susp_dx %> <%= susp_dy %> <%= susp_dz %></size>
          </box>
        </geometry>
      </collision>
      <visual name="visual">
        <geometry>
          <box>
            <size><%= susp_dx %> <%= susp_dy %> <%= susp_dz %></size>
          </box>
        </geometry>
        <material>
          <script>
            <uri>file://media/materials/scripts/gazebo.material</uri>
            <name>Gazebo/Black</name>
          </script>
        </material>
      </visual>
    </link>
    <%= "<joint name=" + '"susp_' + k + '_prismatic" type="prismatic">' %>
      <parent>chassis</parent>
      <%= "<child>susp_" + k + "</child>" %>
      <axis>
        <xyz>0 0 -1</xyz>
        <limit>
          <lower><%= susp_lower %></lower>
          <upper><%= susp_upper %></upper>
        </limit>
        <dynamics>
          <damping><%= susp_damping %></damping>
          <spring_stiffness><%= susp_stiffness %></spring_stiffness>
          <spring_reference><%= susp_spring_center %></spring_reference>
        </dynamics>
      </axis>
      <physics>
        <ode>
          <implicit_spring_damper>1</implicit_spring_damper>
        </ode>
      </physics>
    </joint>
    <%= "<link name=" + '"wheel_' + k + '">' %>
      <pose><%= x0 %> <%= y0 %> <%= wheel_radius %>  <%= -Math::PI/2 %> 0 0</pose>
      <inertial>
        <mass><%= wheel_mass %></mass>
        <inertia>
          <ixx><%= wheel_ixx %></ixx>
          <iyy><%= wheel_iyy %></iyy>
          <izz><%= wheel_izz %></izz>
          <ixy>0</ixy>
          <ixz>0</ixz>
          <iyz>0</iyz>
        </inertia>
      </inertial>
      <collision name="collision">
        <geometry>
          <cylinder>
            <radius><%= wheel_radius %></radius>
            <length><%= wheel_width %></length>
          </cylinder>
        </geometry>
      </collision>
      <visual name="visual">
        <geometry>
          <cylinder>
            <radius><%= wheel_radius %></radius>
            <length><%= wheel_width %></length>
          </cylinder>
        </geometry>
        <material>
          <script>
            <uri>file://media/materials/scripts/gazebo.material</uri>
            <name>Gazebo/Black</name>
          </script>
        </material>
      </visual>
    </link>
    <%= "<joint name=" + '"wheel_' + k + '_spin" type="revolute">' %>
      <%= "<parent>susp_" + k + "</parent>" %>
      <%= "<child>wheel_" + k + "</child>" %>
      <axis>
        <xyz>0 0 1</xyz>
      </axis>
    </joint>
    <% end %>
  </model>
</sdf>