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Activity 8: Writing Your First ROS2 Node — Experiments

Name:

Part 1: Exploring the ROS2 Graph

Q1: Run ros2 node list with turtlesim running. What nodes are listed?

(your answer)

Q2: Run ros2 topic list and fill in the table below. Use ros2 topic info <topic> to find each topic's message type.

Topic Message Type Publisher(s) Subscriber(s)

Q3: Run ros2 topic echo /turtle1/pose --once. What fields does the pose message contain? What is the turtle's starting position and heading?

(your answer)

Q4: Run ros2 node info /turtlesim. List the topics it subscribes to and publishes. What is the difference between these two lists in terms of how you interact with the robot?

Subscribes to (inputs you can send):

Publishes (outputs you can read):

(Ignore the Services and Action sections for now.)

Part 2: Running and Modifying a Publisher Node

Q5: Look at drive_pattern.py. What three ROS2 concepts does the node use? Fill in the table with the specific method call from the code.

ROS2 Concept Method call in drive_pattern.py

Q6: When you run drive_pattern.py, does the turtle draw a perfect square? If not, why? What does this tell you about open-loop control (commanding movement without sensor feedback)?

(your answer)

Q7: Paste the modified section of drive_pattern.py that makes a different shape. What shape did you choose and what values did you change?

Shape:

# Paste your modified code here

Screenshot or description of the result:

Q8: (Crash test) When you drove the turtle into the wall at high speed, what happened? Did the node detect the collision? Did it try to recover or replan? Why not?

(your answer)

Part 3: Connecting to Project 4

Q9: Compute the quaternion values for a goal facing "up" on the map (yaw = 90 degrees = pi/2 radians). Show your work using the formula from the README.

z = sin(_____ / 2) = _____

w = cos(_____ / 2) = _____

Q10: Across activities 5–8, you have used ros2 node list and ros2 topic list (Activity 5), traced lidar data through Cartographer for SLAM (Activity 6), analyzed Nav2 costmap parameters (Activity 7), and now written a publisher node (Activity 8). How do all of these pieces connect for P4 Part 3, where your Python node sends NavigateToPose goals to Nav2?

(your answer)