Skip to content

experiments.md

Latest commit

 

History

History
132 lines (83 loc) · 3.08 KB

experiments.md

File metadata and controls

132 lines (83 loc) · 3.08 KB
Raw

Activity 9: ROS2 Services and Subscriber Nodes — Experiments

Name:

Part 1: ROS2 Services

Q1: Run ros2 service list with turtlesim running. List all the services.

(your answer)

Q2: Run ros2 interface show turtlesim/srv/SetPen. What fields are in the request? What fields (if any) are in the response?

Request fields:

Response fields:

Q3: After calling /spawn to create turtle2, run ros2 topic list. List the new topics that appeared. Why does each turtle get its own separate topics instead of sharing /cmd_vel and /pose?

New topics:

Why separate namespaces:

Q4: Topics and services are both ways for ROS2 nodes to communicate. Give one example of a situation where a service is the right choice and one where a topic is the right choice. Use concrete examples from turtlesim or from Project 4.

Service is better when:

Topic is better when:

Q5: When you called /turtle1/teleport_absolute, the turtle moved instantly — it did not smoothly drive there. What does this tell you about the difference between a service call and publishing a velocity command?

(your answer)

Part 2: Subscriber Node

Q6: In Activity 8, drive_pattern.py used create_timer(). In this activity, wall_avoider.py uses create_subscription(). What triggers timer_callback vs. pose_callback? Why does that difference matter for wall avoidance?

(your answer)

Q7: While wall_avoider.py is running, open a new terminal and run ros2 topic hz /turtle1/cmd_vel. What publish rate do you see? Where does that rate come from?

Rate observed:

Where it comes from:

Q8: Paste your completed pose_callback below — the working version that keeps the turtle inside the walls.

def pose_callback(self, msg):
    # paste your code here

Q9: What happens if you set WALL_MIN = 0.1 (very small buffer)? What happens if you set WALL_MIN = 4.0 (very large buffer)? Test both and describe the behavior.

WALL_MIN = 0.1:

WALL_MIN = 4.0:

Q10 (Extension): Paste your extended pose_callback that uses msg.theta to turn away from the approaching wall. Describe how you used msg.theta in your logic.

def pose_callback(self, msg):
    # paste your extended code here

Explanation of how you used msg.theta:

Part 3: Computation Graph

Q11: Run ros2 node info /turtlesim and ros2 node info /wall_avoider. Fill in the table.

Node Publishes Subscribes to
/turtlesim
/wall_avoider

Q12: The /turtle1/pose topic connects the two nodes. Which node is the publisher and which is the subscriber? How does wall_avoider use what it reads from /turtle1/pose to decide what to write to /turtle1/cmd_vel?

(your answer)

Q13: In Project 4, the Nav2 stack has many nodes communicating over many topics. Based on what you saw with just two nodes (turtlesim + wall_avoider), why is it useful to be able to inspect individual node subscriptions and publications rather than just looking at ros2 topic list?

(your answer)