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Module 09: ROS2 Integration

Introduction​

ROS2 (Robot Operating System 2) is the industry-standard middleware for robot software development. This module covers the architecture and practical use of ROS2 for humanoid robotics.

Section 1: ROS2 Architecture​

1.1 Communication Primitives​

Topic: A named bus for asynchronous, many-to-many communication using publish-subscribe pattern.

Service: Synchronous request-response communication for discrete queries.

Action: Long-running tasks with feedback and cancellation support.

1.2 Node Design​

import rclpy
from rclpy.node import Node
from sensor_msgs.msg import JointState

class JointStatePublisher(Node):
    def __init__(self):
        super().__init__('joint_state_publisher')
        self.pub = self.create_publisher(JointState, 'joint_states', 10)
        self.timer = self.create_timer(0.01, self.publish_state)

    def publish_state(self):
        msg = JointState()
        msg.header.stamp = self.get_clock().now().to_msg()
        msg.name = ['hip', 'knee', 'ankle']
        msg.position = self.get_joint_positions()
        self.pub.publish(msg)

Section 2: Robot Description​

2.1 URDF/XACRO​

URDF (Unified Robot Description Format): XML format describing robot kinematics, dynamics, and visual/collision geometry.

2.2 Robot State Publisher​

Broadcasting transforms from joint states.

Section 3: ros2_control​

3.1 Hardware Interfaces​

Standardized interfaces for actuators and sensors.

3.2 Controllers​

controller_manager:
  ros__parameters:
    update_rate: 500

    joint_state_broadcaster:
      type: joint_state_broadcaster/JointStateBroadcaster

    position_controller:
      type: position_controllers/JointGroupPositionController

Real-time control requires careful system configuration. ROS2 provides tools but doesn't guarantee real-time by default.

Section 4: Navigation and Manipulation​

4.1 Navigation Stack​

  • Map server
  • Localization (AMCL)
  • Path planning
  • Path following

4.2 MoveIt 2​

Motion planning framework for manipulation.

Summary​

Key takeaways:

  1. ROS2 provides standard communication patterns
  2. URDF describes robot structure
  3. ros2_control standardizes hardware interfaces
  4. MoveIt 2 enables motion planning integration

Key Concepts​

  • Topic: Publish-subscribe communication
  • Service: Request-response communication
  • Action: Long-running task with feedback
  • URDF: Robot description format

Further Reading​

  1. ROS2 Documentation: https://docs.ros.org/en/humble/
  2. The Construct ROS2 Courses
  3. MoveIt 2 Tutorials