Chapter 2: Humanoid Robot Simulation in Gazebo

2.1 Humanoid Robot Architecture

Humanoid robots are complex systems with multiple joints, links, and actuators. A typical humanoid robot consists of:

Structural Components:

• Head with sensors (cameras, IMUs)
• Torso providing central structure and power distribution
• Two arms with 7 degrees of freedom (DOF) each
• Two legs with 6 DOF each for bipedal locomotion
• Hands with multiple fingers for manipulation

2.2 URDF Integration with Gazebo

The Unified Robot Description Format (URDF) describes robot structure and physical properties. For humanoid robots, URDF files include:

Link Definition Example:

<link name="right_arm">
  <inertial>
    <mass value="3.5"/>
    <inertia ixx="0.05" iyy="0.05" izz="0.03"/>
  </inertial>
  <visual>
    <geometry>
      <mesh filename="package://robot_description/meshes/arm.dae"/>
    </geometry>
  </visual>
  <collision>
    <geometry>
      <cylinder radius="0.05" length="0.4"/>
    </geometry>
  </collision>
</link>

Joint Definition Example:

<joint name="shoulder_joint" type="revolute">
  <parent link="torso"/>
  <child link="right_arm"/>
  <axis xyz="0 1 0"/>
  <limit lower="-2.0" upper="2.0" effort="50" velocity="2.0"/>
  <dynamics damping="0.1" friction="0.05"/>
</joint>

2.3 Simulating Humanoid Locomotion

Bipedal walking requires coordinated control of multiple joints. Gazebo simulates:

1. Balance Control: Maintaining center of mass within support polygon
2. Joint Trajectories: Smooth motion planning for natural gaits
3. Ground Reaction Forces: Forces generated by feet during stance phase
4. Dynamic Walking: Transitioning between different gaits (walk, run, jog)

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