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CRAZY TURTLE

Demonstration package for ME495. This README is intentionally vague. Figuring out how this package works and filling in the details is part of the exercise. Replace the blanks marked with ${ITEM} with your answer. Keep the backticks but remove the ${}, so ${ITEM} becomes My Answer. Unless otherwise specified, list the command and all arguments that you passed to it.

Repository Configuration

  1. The crazy_turtle git repository consists of the ROS 2 packages crazy_turtle and crazy_turtle_interfaces.
  2. The package crazy_turtle is a ament python package.
  3. The package crazy_turtle_interfaces is a ament_cmake package.

Setup Instructions

  1. Build the workspace using colcon build --symlink-install so that it is unnecessary to rebuild when python files change.
  2. Initialize the ROS environment (i.e., set the necessary ROS environment variables) by executing source install/setup.bash
  3. Make sure no other ROS nodes are running prior to starting by inspecting the results of ros2 node list.
  4. Run the launchfile go_crazy_turtle.launch.xml by executing ros2 launch crazy_turtle go_crazy_turtle.launch.xml
  5. When running you can see a visual depiction of the ROS graph using the rqt_graph command. The ROS graph, including all topics and node labels, looks like: The ROS Graph

Runtime Information

The launchfile from above should be running at all times when executing these commands. If the nodes launched from the launchfile are not running, you will get incorrect results.

  1. Use the ROS command ros2 node list to list all the nodes that are running. The output of the command looks like

    /mover
/roving_turtle
/rqt_gui_py_node_7584

  2. Use the ROS command ros2 topic list to list the topics The output of the command looks like

    /parameter_events
/rosout
/turtle1/cmd_vel
/turtle1/color_sensor
/turtle1/pose

  3. Use the ROS command ros2 topic hz /turtle1/cmd_vel to verify that the frequency of the /turtle1/cmd_vel topic is ros2 topic hz /turtle1/cmd_vel Hz

  4. Use the ROS command ros2 service list to list the services. The output of the command looks like

    /clear
/kill
/mover/describe_parameters
/mover/get_parameter_types
/mover/get_parameters
/mover/get_type_description
/mover/list_parameters
/mover/set_parameters
/mover/set_parameters_atomically
/reset
/roving_turtle/describe_parameters
/roving_turtle/get_parameter_types
/roving_turtle/get_parameters
/roving_turtle/get_type_description
/roving_turtle/list_parameters
/roving_turtle/set_parameters
/roving_turtle/set_parameters_atomically
/rqt_gui_py_node_7584/describe_parameters
/rqt_gui_py_node_7584/get_parameter_types
/rqt_gui_py_node_7584/get_parameters
/rqt_gui_py_node_7584/get_type_description
/rqt_gui_py_node_7584/list_parameters
/rqt_gui_py_node_7584/set_parameters
/rqt_gui_py_node_7584/set_parameters_atomically
/spawn
/switch
/turtle1/set_pen
/turtle1/teleport_absolute
/turtle1/teleport_relative

  5. Use the ROS command ros2 service type /switch to determine the type of the /switch service, which is crazy_turtle_interfaces/srv/Switch.

  6. Use the ROS command ros2 param list to list the parameters of all running nodes

    /mover:
  start_type_description_service
  use_sim_time
  velocity

/roving_turtle: background_b background_g background_r holonomic qos_overrides./parameter_events.publisher.depth qos_overrides./parameter_events.publisher.durability qos_overrides./parameter_events.publisher.history qos_overrides./parameter_events.publisher.reliability start_type_description_service use_sim_time ```

  1. Use the ROS command ros2 param describe /mover velocity to get information about the /mover velocity parameter, including its type, description, and constraints

Parameter name: velocity Type: double Description: The velocity of the turtle Constraints: ```

  1. Use the ROS command ros2 interface show crazy_turtle_interfaces/srv/Switch to retrieve a template/prototype for entering parameters for the /switch service on the command line.

turtlesim/Pose mixer # use a strange formula to set the new location of the turtle float32 x float32 y float32 theta float32 linear_velocity float32 angular_velocity

float64 x # the new x position of the new turtle float64 y # the new y position of the new ```

Package Exploration

  1. Use the ROS command ros2 interface package crazy_turtle_interfaces to list the interface types defined by crazy_turtle_interfaces The output of the command looks like 
    crazy_turtle_interfaces/srv/Switch
  2. Use the ROS command ros2 pkg executables crazy_turtle to list the executables included with the crazy_turtle package The output of the command looks like 
    crazy_turtle mover

Live Interaction

  1. Use the command ros2 param get /mover velocity to retrieve the value of the /mover velocity parameter, which is 4.5.
  2. The ROS command to call the /switch service, and it's output is listed below: 
    ros2 service call /switch crazy_turtle_interfaces/srv/Switch "{mixer: {x: 1.0, y: 2.0, theta: 0.0, angular_velocity: 3.0, linear_velocity: 4.0}}"
requester: making request: crazy_turtle_interfaces.srv.Switch_Request(mixer=turtlesim.msg.Pose(x=1.0, y=2.0, theta=0.0, linear_velocity=4.0, angular_velocity=3.0))

response:
crazy_turtle_interfaces.srv.Switch_Response(x=5.0, y=4.0)
  3. The switch service performs the following actions (in sequence):
    1. It kills the current turtle
    2. It then respawns a new turtle at (y + angular_velocity, x + linear_velocity)
  4. What happens to the turtle's motion if you use ros2 param set /mover velocity 10.0 to change /mover velocity to 10? same
  5. Use the Linux command kill $(ps ax | grep /mover | grep ros | awk '{print $1}') to kill the /mover node.
  6. Use the ROS command ros2 run crazy_turtle mover --ros-args -p velocity:=10.0 -r /cmd_vel:=/turtle1/cmd_vel to start the /mover node with a velocity of 10.
    • Be sure to remap cmd_vel to /turtle1/cmd_vel.
  7. What happened to the turtle's velocity after relaunching mover? faster