ROS 2 Ackermann Controller#

Learning Objectives#

In this example, we will drive a forklift by subscribing to a AckermannDriveStamped message through the ROS network. We will learn to

  • Setup Articulation and Ackermann controllers to a forklift

  • Setup the robot to be driven by a ROS2 AckermannDriveStamped message

Getting Started#

Important

Make sure to source your ROS 2 installation from the terminal before running Isaac Sim. If sourcing ROS 2 is a part of your bashrc then Isaac Sim can be run directly.

Prerequisite

  • This ROS2 Ackermann Controller sample is only supported on ROS2 Foxy and Humble.

  • The ackermann_msgs ROS2 package is required to run this sample. To install this package run the following command:

    sudo apt install ros-humble-ackermann-msgs

    Warning

    ROS 2 Foxy is no longer tested or supported. This may result in potential issues when ROS 2 Foxy is used in conjunction with Isaac Sim 4.2 or later. ROS 2 Foxy Isaac Sim tutorial packages will be removed in a future release.

    sudo apt install ros-foxy-ackermann-msgs

  • Enable the omni.isaac.ros2_bridge Extension in the Extension Manager window by navigating to Window > Extensions.

  • This tutorial requires isaac_tutorials ROS2 package which is provided in IsaacSim-ros_workspaces repo. Complete ROS and ROS 2 Installation to make sure the ROS2 workspace environment is setup correctly.

Ackermann Controller and Drive Setup#

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

  2. Add the Forklift C robot by going to Create -> Isaac -> Robots -> Wheeled Robots -> Forklift -> Forklift C.

  3. Create a new action graph by navigating to Window > Visual Scripting > Action Graph and then in the Action Graph panel, select New Action Graph.

  4. Now add the following nodes to the graph and connect them as shown:

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

    • ROS2 Context node to create a context using either the given Domain ID or the ROS_DOMAIN_ID environment variable.

    • Isaac Compute Odometry Node node to compute the robot’s current linear speed.

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

    • ROS2 Subscribe AckermannDrive node to subscribe to Ackermann drive commands.

    • In the Property tab for the Isaac Compute Odometry Node:

      • Add the Forklift prim (ie. /Forklift) to its chassisPrim input field. This node calculates the position of the robot relative to its start location. Its linear velocity output will be fed into the Ackermann Controller node.

    • In the Property tab for the ROS2 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

      invertSteeringAngle

      True

      maxWheelRotation

      0.69813

      maxWheelVelocity

      20.0

      trackWidth

      0.82

      turningWheelRadius

      0.255

      useAcceleration

      True

      wheelBase

      1.65

  5. Add the following nodes to the graph and modify them as explained:

    • Articulation Controller node to manipulate the wheels of the forklift. In the Property tab:

      • Add the Forklift prim (ie. /Forklift) to its targetPrim input field.

      • For the jointNames input field:

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

        • click the Add Element button again and enter right_back_wheel_joint in the text field that appears.

    • Make Array node to create an array of wheel rotation velocities to feed into the articulation controller. In the Property tab:

      • Under the input0 field click the plus icon to add a second input.

    • Now connect the nodes as shown:

  6. Add another set of these nodes to the graph and modify them as explained:

    • Articulation Controller node to manipulate the steering angle of the forklift wheels. In the Property tab:

      • Add the Forklift prim (ie. /Forklift) to its targetPrim input field.

      • For the jointNames input field:

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

        • click the Add Element button again and enter right_rotator_joint in the text field that appears.

    • Make Array node to create an array of wheel angles to feed into the articulation controller. In the Property tab:

      • Under the input0 field click the plus icon to add a second input.

    • Now connect the nodes as shown:

  7. Hit Play in Isaac Sim to start simulation.

  8. In a new terminal, ensure 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

    The forklift should move similarly to the one below:

    ROS2 AckermannDrive Tutorial forklift movement

Summary#

This tutorial covered

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

  2. Adding a ROS2 AckermannDriveStamped subscriber node which feeds commands into the Ackermann Controller node.

Next Steps#

Continue on to the next tutorial in our ROS2 Tutorials series, ROS 2 Launch.

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