Gazebo model — Bouncing Ball

Launch

• Check the SDFCopy

  gz sdf -k Bouncing_Ball/model.sdf

  Validate the model against the SDFormat spec before running it.

• Run in GazeboCopy

  GZ_SIM_RESOURCE_PATH=$PWD gz sim -r -v4 bondgraph_world.sdf

  Launch gz-sim with the generated world. The resource path lets `model://` find the package folder.

• Watch joint statesCopy

  gz topic -e -t /world/bondgraph_world/model/Bouncing_Ball/joint_state

  Stream joint positions and velocities so they can be compared against the bond graph run.

• ROS 2Copy

  ros2 launch ros_gz_sim gz_sim.launch.py gz_args:="-r bondgraph_world.sdf"

  Same world through ros_gz_sim, when the model is part of a ROS 2 stack.

The mechanism: links, inertia tensors, joints and dynamics.

<?xml version="1.0" ?>
<!-- Generated by BondGraph Studio (https://xn--lda.se) — SDFormat for Gazebo -->
<!-- Gravity 9.81 m/s² along -Z, inferred from gravity. -->
<sdf version="1.9">
  <model name="Bouncing_Ball">
    <self_collide>false</self_collide>

    <link name="base_link">
      <gravity>false</gravity>
      <inertial>
        <mass>1</mass>
        <inertia><ixx>0.001</ixx><ixy>0</ixy><ixz>0</ixz><iyy>0.001</iyy><iyz>0</iyz><izz>0.001</izz></inertia>
      </inertial>
    </link>
    <joint name="base_link_world_joint" type="fixed">
      <parent>world</parent>
      <child>base_link</child>
    </joint>

    <link name="mass">
      <pose relative_to="mass_joint">0 0 0 0 0 0</pose>
      <gravity>true</gravity>
      <inertial>
        <pose>0 0 0 0 0 0</pose>
        <mass>1</mass>
        <inertia>
          <ixx>0.00166667</ixx><ixy>0</ixy><ixz>0</ixz>
          <iyy>0.00166667</iyy><iyz>0</iyz><izz>0.00166667</izz>
        </inertia>
      </inertial>
      <visual name="mass_visual">
        <pose>0 0 0 0 0 0</pose>
        <geometry>
          <box><size>0.1 0.1 0.1</size></box>
        </geometry>
        <material>
          <ambient>0.85 0.55 0.2 1</ambient>
          <diffuse>0.85 0.55 0.2 1</diffuse>
        </material>
      </visual>
      <collision name="mass_collision">
        <pose>0 0 0 0 0 0</pose>
        <geometry>
          <box><size>0.1 0.1 0.1</size></box>
        </geometry>
        <surface>
          <friction>
            <ode><mu>1</mu><mu2>1</mu2></ode>
          </friction>
        </surface>
      </collision>
    </link>
    <joint name="mass_joint" type="prismatic">
      <pose relative_to="base_link">0 0 0 0 0 0</pose>
      <parent>base_link</parent>
      <child>mass</child>
      <axis>
        <xyz>0 0 1</xyz>
        <limit>
          <lower>-1</lower>
          <upper>1</upper>
          <effort>1000</effort>
          <velocity>100</velocity>
        </limit>
        <dynamics>
          <damping>0</damping>
          <friction>0</friction>
          <spring_stiffness>1e-9</spring_stiffness>
          <spring_reference>0</spring_reference>
        </dynamics>
      </axis>
    </joint>
  </model>
</sdf>

Physics parity

Gravity 9.81 m/s² along -Z, inferred from gravity.

• Gravity in the world file (0 0 -9.81 m/s²) is the gravity the bond graph run assumed — if you change it, the two will diverge.
• Link masses and inertia tensors in model.sdf match the Physics panel of the geometry view exactly; both come from the same exporter.
• Joint damping, Coulomb friction and spring stiffness come from the R and C elements on each DOF — a mismatch means a hint or parameter changed after export.
• Contact is the one thing the bond graph does not model: impacts in Gazebo follow the surface friction and restitution in model.sdf, not the graph.
• Echo /world/bondgraph_world/model/Bouncing_Ball/joint_state while the world runs and plot it against the simulation results to compare trajectories.