ROS 2 Ackermann Controller#

Learning Objectives#

In this example, you learn to drive a Leatherback car by subscribing to a AckermannDriveStamped message through the ROS network. You will learn to:

  • Setup Articulation and Ackermann Controllers to a Leatherback

  • Setup the robot to be driven by a ROS 2 AckermannDriveStamped message

  • Control an Ackermann base robot with a Twist message

Getting Started#

Prerequisite

  • The ackermann_msgs ROS 2 package is required to run this sample. To install this package run the following command:

    sudo apt install ros-humble-ackermann-msgs

  • Enable the isaacsim.ros2.bridge Extension in the Extension Manager window by navigating to Window > Extensions.

  • This tutorial requires isaac_tutorials and cmdvel_to_ackermann ROS 2 packages which are provided in IsaacSim-ros_workspaces repo. Complete ROS 2 Installation to make sure the ROS 2 workspace environment is setup correctly.

Ackermann Controller and Drive Setup#

  1. In a new stage, create the Flat Grid environment by going to Create > Environments > Flat Grid.

  2. Add the Leatherback robot by going to the Content Browser, click Isaac Sim>ROBOTS>NVIDIA>Leatherback.

  3. Drag and drop the leatherback.usd asset in scene/stage window. Ensure that it is placed at the origin by zero’ing out all the Translate components in the Transform Property.

  4. Create a new action graph by navigating to Window > Graph Editors > Action Graph.

  5. In the Action Graph panel, select New Action Graph.

  6. Add the following nodes to the graph and connect them as shown:

    • On Playback Tick node to execute other graph nodes every simulation frame.

    • ROS 2 Context node to create a context using either the given Domain ID or the ROS_DOMAIN_ID environment variable.

    • Ackermann Controller node to compute individual wheel steering angles and wheel speed.

    • ROS 2 Subscribe AckermannDrive node to subscribe to Ackermann drive commands.

    • ROS 2 QoS Profile node to create a QoS profile.

    • Articulation Controller node to manipulate the steering joints of the Leatherback. In the Property tab:

      • Add the Leatherback prim (that is. /Leatherback) to its targetPrim input field.

      • For the jointNames input field:

        • Click Add Element and enter Knuckle__Upright__Front_Left in the text field that appears.

        • Click Add Element again and enter Knuckle__Upright__Front_Right in the text field that appears.

    • Articulation Controller_01 node to manipulate the wheels of the Leatherback. In the Property tab:

      • Add the Leatherback prim (that is. /Leatherback) to its targetPrim input field.

      • For the jointNames input field:

        • Click Add Element and enter Wheel__Upright__Rear_Left in the text field that appears.

        • Click Add Element again and enter Wheel__Upright__Rear_Right in the text field that appears.

        • Click Add Element again and enter Wheel__Knuckle__Front_Left in the text field that appears.

        • Click Add Element again and enter Wheel__Knuckle__Front_Right in the text field that appears.

    ROS 2 AckermannDrive Tutorial graph 1

    ActionGraph setup#

    • In the Property tab for the ROS 2 Subscribe AckermannDrive node:

      • Ensure the topicName input field is set to ackermann_cmd.

    • In the Property tab for the Ackermann Controller node set inputs as shown in the table below:

    Input Field

    Value

    backWheelRadius

    0.052

    frontWheelRadius

    0.052

    maxWheelRotation

    0.7854

    maxWheelVelocity

    20.0

    trackWidth

    0.24

    wheelBase

    0.32

    maxAcceleration

    1.0

    maxSteeringAngleVelocity

    1.0

  7. Hit Play in Isaac Sim to start simulation.

  8. In a new terminal, verify that your Isaac Sim ROS workspace is sourced and run the following node to start publishing Ackermann commands:

    ros2 run isaac_tutorials ros2_ackermann_publisher.py

    Verify that the Leatherback car moves similarly to the one below:

ROS 2 AckermannDrive Tutorial Leatherback movement

Note

Preconfigured Leatherback Assets

  • Leatherback asset with action graph is located at Isaac Sim>Sample>ROS2>Robots>Leatherback_ROS in the Content Browser.

  • Leatherback warehouse with race track scene is located at Isaac Sim>Sample>ROS2>Scenario>leatherback_ackermann in the Content Browser.

Converting Twist Messages to AckermannDriveStamped Messages#

To control the Leatherback robot using your keyboard by translating command velocity to Ackermann drive stamped messages:

  1. Open the Leatherback warehouse with race track scene by going to the Content Browser Isaac Sim>Sample>ROS2>Scenario>leatherback_ackermann.

  2. Press PLAY to start the simulation.

  3. Stop the previous publisher.

  4. In a new terminal, verify that your Isaac Sim ROS workspace is sourced and run the following node to start publishing Ackermann commands from cmd_vel.

    ros2 launch cmdvel_to_ackermann cmdvel_to_ackermann.launch.py acceleration:=0.5 steering_velocity:=0.5

    Note

    launch parameters

    • publish_period_ms (default_value=20): publishing dt (ms)

    • track_width (default_value=0.2): wheel separation distance (m)

    • acceleration (default_value=0.0): acceleration, 0 means change speed as quickly as possible (ms^-2)

    • steering_velocity (default_value=0.0): delta steering angle, 0 means change angle as quickly as possible (radians/s)

  5. In a separate terminal, source ROS and launch teleop_twist_keyboard or another desired package to publish Twist messages:

    ros2 run teleop_twist_keyboard teleop_twist_keyboard

You can now control the Leatherback robot using your keyboard. Try the controls. For example, test that you can stay on the racetrack.

  • Forward: i

  • Backward: ,

  • Forward Left: u

  • Forward Right: o

  • Backward Left: m

  • Backward Right: .

  • Stop: k

ROS 2 AckermannDrive Tutorial Leatherback manual control

Summary#

This tutorial covered:

  1. Creating and setting up an Ackermann Controller node and with articulation controller nodes.

  2. Adding a ROS 2 AckermannDriveStamped subscriber node, which feeds commands into the Ackermann Controller node.

  3. Translating the command velocity to AckermannDriveStamped message and control an Ackermann based robot with keyboard.

Next Steps#

Continue on to the next tutorial in our ROS 2 Tutorials series, Running a Reinforcement Learning Policy through ROS2 and Isaac Sim to learn how to configure a robot to run a locomotion policy in Isaac Sim with ROS 2.