Exercises
=========

These short hands-on tasks map to the 3-day schedule and include verification
commands so students can confirm progress quickly.

Exercise 1 — Hello ROS (Day 0)
- Goal: run talker/listener and become comfortable with the `ros2` CLI
- Steps:
  1. Open a terminal and source the ROS distro and (if present) your workspace:
```bash
# replace <distro> with `humble` or `jazzy` as appropriate
source /opt/ros/<distro>/setup.bash
# if you've built a workspace in this shell, also source it:
source install/setup.bash
```
  2. Run a demo publisher: `ros2 run demo_nodes_py talker`
  3. In another terminal (also sourced): `ros2 run demo_nodes_py listener`
- Verify: you will see messages printed by the listener and can use
  `ros2 topic list` / `ros2 topic echo` to inspect active topics.

Exercise 2 — URDF building & visualization (Day 1)
- Goal: build the robot description (URDF/XACRO), publish `robot_description`, and visualize the model in RViz
- Steps:
  1. Ensure workspace is built and sourced:
```bash
colcon build --packages-select pendulum_description
source /opt/ros/<distro>/setup.bash
source install/setup.bash
```
  2. Generate a URDF from the XACRO (optional check):
```bash
# run from workspace root; update path if needed
xacro src/pendulum_description/description/robot.urdf.xacro -o /tmp/pendulum.urdf
```
  3. Launch the URDF visualization (this publishes `robot_description`):
```bash
ros2 launch pendulum_description urdf.launch.py use_rviz:=true
```
  4. Inspect topics and transforms:
```bash
ros2 topic list
ros2 topic echo /joint_states
ros2 run rqt_graph rqt_graph
```
- Verify: RViz shows the pendulum model, `tf` frames exist, and the
  `joint_state_publisher_gui` (if launched) moves joints interactively.

Exercise 3 — Simulator exploration (Day 2)
- Goal: launch the pendulum world and inspect topics bridged from Gazebo
- Steps:
  1. Launch Gazebo with the pendulum world:
```bash
ros2 launch pendulum_sim gazebo.launch.py
```
  2. Use the bridge config to find exact topic names and inspect:
```bash
ros2 topic list
ros2 topic echo /joint_states
```
- Verify: joint state messages stream and Gazebo shows the pendulum.

Future / Day 3 (planned)
- Once `pendulum_control` is present: implement and run a simple PID
  controller node, expose PID gains as parameters, and iterate tuning.

Stretch tasks
- Add an encoder noise model in the simulator and log results with `ros2 bag`
- Implement a ROS2 action that performs a controlled swing-up routine