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 ROS AckermannDriveStamped message

Getting Started#

Prerequisite

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

    sudo apt install ros-noetic-ackermann-msgs

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

  • ROS Bridge is enabled.

  • roscore is running.

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.

    • 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.

    • ROS1 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 ROS1 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.

    rosrun isaac_tutorials ros_ackermann_publisher.py

    The forklift should move similarly to the one below:

    ROS1 AckermannDrive Tutorial forklift movement

Summary#

This tutorial covered

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

  2. Adding a ROS1 AckermannDriveStamped subscriber node which feeds commands into the Ackermann Controller node.

Next Steps#

Continue on to the next tutorial in our ROS Tutorials series, ROS 1 to ROS 2 to learn how to interface with ROS2 nodes in Isaac Sim from ROS1.

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