RB1 ROS2 Description Package

This package contains a ROS2 robot model description for Robotnik's RB-1 mobile base with ROS2 Control integration for both differential drive and elevator control.

Overview

The package provides:

• Complete URDF/XACRO robot description for the RB1 robot
• ROS2 Control integration with Gazebo simulation
• Differential drive controller for robot mobility
• Position controller for elevator platform
• Automatic controller spawning and configuration

Installation

1. Clone this repository into your ROS2 workspace:

   cd ~/ros2_ws/src
   git clone <repository-url>

2. Build the package:

   cd ~/ros2_ws
   colcon build
   source install/setup.bash

Usage

Starting the Simulation

Launch the complete simulation with automatic controller spawning:

ros2 launch rb1_ros2_description rb1_ros2_xacro.launch.py

This will:

1. Start Gazebo with an empty world
2. Spawn the RB1 robot
3. Load the gazebo_ros2_control plugin
4. Automatically spawn and activate all controllers:
   • joint_state_broadcaster (at 130 seconds)
   • rb1_base_controller (at 130 seconds)
   • elevator_controller (at 130 seconds)

Verifying the Setup

Check that all controllers are active:

# List all active controllers
ros2 control list_controllers

# Check hardware interfaces
ros2 control list_hardware_interfaces

# Verify topics are available
ros2 topic list | grep -E "(cmd_vel|elevator)"

Expected output:

joint_state_broadcaster[joint_state_broadcaster/JointStateBroadcaster] active
rb1_base_controller[diff_drive_controller/DiffDriveController] active
elevator_controller[position_controllers/JointGroupPositionController] active

Robot Movement Commands

Differential Drive Control

Move the robot using velocity commands:

# Move forward
ros2 topic pub --rate 10 /rb1_base_controller/cmd_vel_unstamped geometry_msgs/msg/Twist \
  "{linear: {x: 0.3, y: 0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 0.0}}"

# Rotate in place
ros2 topic pub --rate 10 /rb1_base_controller/cmd_vel_unstamped geometry_msgs/msg/Twist \
  "{linear: {x: 0.0, y: 0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 0.3}}"

# Combined movement (forward + turn)
ros2 topic pub --rate 10 /rb1_base_controller/cmd_vel_unstamped geometry_msgs/msg/Twist \
  "{linear: {x: 0.3, y: 0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 0.3}}"

# Stop the robot
ros2 topic pub --once /rb1_base_controller/cmd_vel_unstamped geometry_msgs/msg/Twist \
  "{linear: {x: 0.0, y: 0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 0.0}}"

Keyboard Teleoperation

Control the robot with keyboard:

ros2 run teleop_twist_keyboard teleop_twist_keyboard --ros-args --remap cmd_vel:=/rb1_base_controller/cmd_vel_unstamped

Elevator Control Commands

Control the elevator platform height:

# Check if elevator controller is active
ros2 control list_controllers | grep elevator

# Raise elevator to maximum height (30cm)
ros2 topic pub --once /elevator_controller/commands std_msgs/msg/Float64MultiArray "{data: [0.3]}"

# Lower elevator to minimum height (ground level)
ros2 topic pub --once /elevator_controller/commands std_msgs/msg/Float64MultiArray "{data: [0.0]}"

# Set elevator to middle position (15cm)
ros2 topic pub --once /elevator_controller/commands std_msgs/msg/Float64MultiArray "{data: [0.15]}"

# Set elevator to 1/4 height (7.5cm)
ros2 topic pub --once /elevator_controller/commands std_msgs/msg/Float64MultiArray "{data: [0.075]}"

# Set elevator to 3/4 height (22.5cm)
ros2 topic pub --once /elevator_controller/commands std_msgs/msg/Float64MultiArray "{data: [0.225]}"

Monitor Elevator Position

Check current elevator position:

# Monitor joint states
ros2 topic echo /joint_states

# Monitor elevator controller output
ros2 topic echo /elevator_controller/controller_state

Troubleshooting

Controllers Not Loading

If controllers fail to spawn automatically:

# Manually spawn controllers
ros2 run controller_manager spawner joint_state_broadcaster --controller-manager /controller_manager
ros2 run controller_manager spawner rb1_base_controller --controller-manager /controller_manager  
ros2 run controller_manager spawner elevator_controller --controller-manager /controller_manager

Robot Not Moving

1. Verify controllers are active:

   ros2 control list_controllers

2. Check if hardware interfaces are claimed:

   ros2 control list_hardware_interfaces

Elevator Not Responding

1. Check if elevator controller is loaded:

   ros2 control list_controllers | grep elevator

2. Verify the elevator joint exists:

   ros2 topic echo /joint_states | grep elevator

Configuration Files

• Launch file: launch/rb1_ros2_xacro.launch.py
• Robot description: xacro/rb1_ros2_base.urdf.xacro
• Controller config: config/rb1_controller.yaml

ROS2 Control Architecture

The robot uses ROS2 Control with the following components:

• Hardware Interface: gazebo_ros2_control/GazeboSystem
• Controllers:
  • diff_drive_controller/DiffDriveController
  • position_controllers/JointGroupPositionController
  • joint_state_broadcaster/JointStateBroadcaster