AWS DeepRacer Cmdvel to Servo Package

Overview

The cmdvel to servo ROS package creates the cmdvel_to_servo_node which decides the action messages (servo control messages specifically angle and throttle) to be sent out after converting the cmd_vel. For detailed information, see Introduction to the ROS Navigation stack using AWS DeepRacer Evo.

License

The source code is released under Apache 2.0.

Installation

Prerequisites

The cmdvel_to_servo_pkg specifically depends on the following ROS2 packages as build and run dependencies:

1. deepracer_interfaces_pkg: This package contains the custom message and service type definitions used across the AWS DeepRacer core application, modified to support the ROS Nav2 integration packages.

Downloading and building

Open up a terminal on the AWS DeepRacer device and run the following commands as the root user.

1. Switch to the root user before you source the ROS2 installation:

    sudo su
   

2. Source the ROS2 Foxy setup bash script:

    source /opt/ros/foxy/setup.bash 
   

3. Create a workspace directory for the package:

    mkdir -p ~/deepracer_nav2_ws
    cd ~/deepracer_nav2_ws
   

4. Clone the entire AWS DeepRacer package on the DeepRacer device.

    git clone https://github.com/aws-deepracer/aws-deepracer.git
    cd ~/deepracer_nav2_ws/aws-deepracer
   

5. Fetch the unreleased dependencies:

    cd ~/deepracer_nav2_ws/aws-deepracer/deepracer_nodes
    rosws update
   

6. Resolve the dependencies:

    cd ~/deepracer_nav2_ws/aws-deepracer/deepracer_nodes && rosdep install -i --from-path . --rosdistro foxy -y
   

7. Build the cmdvel_to_servo_pkg and deepracer_interfaces_pkg:

    cd ~/deepracer_nav2_ws/aws-deepracer/ && colcon build --packages-select deepracer_interfaces_pkg cmdvel_to_servo_pkg
   

Using the cmdvel_to_servo_node

Although the cmdvel_to_servo_node is built to work with the ROS Nav2 integration packages, you can run it independently for development, testing, and debugging purposes.

Running the node

To launch the built cmdvel_to_servo_node as the root user on the AWS DeepRacer device, open another terminal on the AWS DeepRacer device and run the following commands as the root user.

1. Switch to the root user before you source the ROS2 installation:

    sudo su
   

2. DeepRacer ROS Nav2 workspace:

    cd ~/deepracer_nav2_ws/aws-deepracer/
   

3. Source the ROS2 Foxy setup bash script:

    source /opt/ros/foxy/setup.bash 
   

4. Source the setup script for the installed packages:

    source ~/deepracer_nav2_ws/aws-deepracer/install/setup.bash
   

5. Launch the cmdvel_to_servo_node using the launch script:

    ros2 launch cmdvel_to_servo_pkg cmdvel_to_servo_pkg_launch.py
   

Changing the MAX_SPEED scale of the AWS DeepRacer

You can modify the MAX_SPEED scale of the AWS DeepRacer using a ROS2 service call in case the car isn’t moving as expected. This can occur because of the vehicle battery percentage, the surface on which the car is operating, or for other reasons.

1. Switch to the root user before you source the ROS2 installation:

    sudo su
   

2. Navigate to the ROS Nav2 workspace:

    cd ~/deepracer_nav2_ws/aws-deepracer/
   

3. Source the ROS2 Foxy setup bash script:

    source /opt/ros/foxy/setup.bash
   

4. Source the setup script for the installed packages:

    source ~/deepracer_nav2_ws/aws-deepracer/install/setup.bash
   

5. Change the MAX SPEED to xx% of the MAX Scale:

    ros2 service call /cmdvel_to_servo_pkg/set_max_speed deepracer_interfaces_pkg/srv/SetMaxSpeedSrv "{max_speed_pct: 0.xx}"
   

   Example: Change the MAX SPEED to 75% of the MAX Scale:

    ros2 service call /cmdvel_to_servo_pkg/set_max_speed deepracer_interfaces_pkg/srv/SetMaxSpeedSrv "{max_speed_pct: 0.75}"
   

Launch files

The cmdvel_to_servo_pkg_launch.py launch file included in this package gives an example of how to launch the cmdvel_to_servo_node.

    from launch import LaunchDescription
    from launch_ros.actions import Node

    def generate_launch_description():
        return LaunchDescription([
            Node(
                package='cmdvel_to_servo_pkg',
                namespace='cmdvel_to_servo_pkg',
                executable='cmdvel_to_servo_node',
                name='cmdvel_to_servo_node'
            )
    ])

Node details

cmdvel_to_servo

Subscribed topics

Published topics

Services

Resources

• Getting started with AWS DeepRacer OpenSource
• Introduction to the ROS Navigation stack using AWS DeepRacer Evo