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Focus: Physics simulation and environment building.

Heading Breakdown​

Focus: Physics simulation and environment building directs our attention to the creation of the virtual world. Physics simulation is the mathematical approximation of the laws of nature—gravity, friction, momentum—that governs how objects move and interact. Environment building is the construction of the stage upon which the robot acts—the walls, floors, tables, and terrains. The importance is absolute for validation; a robot that walks on a flat plane in a void has not been tested. It must walk on slippery floors, uneven grass, and cluttered rooms. Real usage involves designing a "Digital Twin" of a factory floor to test if the robot fits in the aisles. An example is using SDF (Simulation Description Format) to define a world with a specific sun angle and shadow softness. This is key for upgradable high-DoF humanoids because it allows us to test "what if" scenarios (e.g., "What if the robot carries a 10kg box?") without risking the hardware.

Training Focus: Environmental Fidelity​

We focus on context. A robot exists in a context.

  • Static vs. Dynamic: Walls don't move; people do. We learn to model both.
  • Material Properties: Friction coefficients are critical for walking robots.

Detailed Content​

The Gazebo World​

A .sdf file that defines the scene.

  • Physics Engines: ODE (Open Dynamics Engine), Bullet, Dart, Simbody.
  • Lighting: Ambient, Point, and Directional lights.
  • GUI: Using the Gazebo visual editor to drag-and-drop assets.

Industry Vocab​

  • SDF: Simulation Description Format.
  • Mesh: The 3D geometry.
  • Collision Box: A simplified shape used for physics calculations to save CPU.

Code Example: World SDF​

<!-- Defensive World Definition -->
<sdf version="1.6">
  <world name="default">
    <!-- Global Light Source -->
    <include>
      <uri>model://sun</uri>
    </include>
    <!-- Ground Plane with specific friction -->
    <model name="ground_plane">
      <static>true</static>
      <link name="link">
        <collision name="collision">
          <geometry><plane><normal>0 0 1</normal><size>100 100</size></plane></geometry>
          <surface>
            <friction>
              <ode><mu>100</mu><mu2>50</mu2></ode>
            </friction>
          </surface>
        </collision>
        <visual name="visual">
          <geometry><plane><normal>0 0 1</normal><size>100 100</size></plane></geometry>
        </visual>
      </link>
    </model>
  </world>
</sdf>

Real-World Use Case: Warehouse Sim​

For the G1, we build a warehouse world with concrete floors (low friction) and rubber mats (high friction). We test the walking controller's ability to transition between these surfaces without slipping.