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Session 3

Warm-up Excercise​

Open the turtlesim simulator:

ros2 run turtlesim turtlesim_node

To control the linear and angular velocities make sure to publish in the topic: /turtle1/cmd_vel, and the message type is geometry_msgs/msg/Twist.

Your task is to write a publisher that drive the turtle in a way that draw a circle.

Services​

ROS Services

Task - Turtle Controller​

Create a ROS 2 node using python that publishes velocity commands to turtlesim and exposes two services to control motion.

Requeriments:

  • Node name: turtle_controller
    • Publisher:
      • topics: /turtle1/cmd_vel
      • type: geometry_msgs/msg/Twist
      • rate: 10 Hz
    • Services:
      • /start: When called enable motion.
        • type: std_srvs/srv/Trigger
      • /stop: When called disable motion.
        • type: std_srvs/srv/Trigger

Actions​

ROS Actions

ROS Python Client (rclpy) Documentation​

You can find the official python client documentation, rclpy to get all the information about the available functions that you can perform with the pythonn client.

Keep in mind the the client documentation pointing to the rolling distribution (the latest dev branch) and some functions may not be implemented in your distribution (e.g. Humble).