Introduction

The goals of this lab are to gain experience working with PID controllers, launch files, and the ROS parameter server.

RocketBot PID

• If you haven't already, run the account configuration script: ros_config_account.sh.

• Accept the PID lab assignment invitation posted to Piazza. The repository page for this lab already contains the starter code that you will be using. Clone the repository into your workspace folder:

  cd ~/catkin_ws/src
  git clone GIT_URL pid_practice

• Take a minute to read over the file guidance.py in the scripts directory, and the file rocket.launch in the launch directory. Make sure you understand the contents of those files. Build your workspace and source ~/catkin_ws/devel/setup.bash.

• Start ROS using the roscore command.

• Launch rocket.launch in a separate terminal:

  roslaunch pid_practice rocket.launch

  You can change the target altitude by clicking in the RocketBot simulator window.

• Modify guidance.py so that it reads the PID gain parameters from the parameter server and uses the PID controller provided in pid.py to control the y-component of the thrust.

• Use the rosparam command line utility to set the three parameters expected by guidance.py to some initial values and re-launch.

• Experiment with different values for your gain parameters until you find settings that work well. The rocket should rise smoothly to the target altitude with minimal overshoot and oscillations. (I suggest resetting the PID controller when the target location changes. Otherwise the D term will experience a large transient value that could cause significant overshoot.)

• Once you are satisfied with your gain parameters, modify rocket.launch to set the parameters appropriately. The launch file XML format is described on this wiki page. Test the new launch file. Once everything is working, commit and push your changes. Make sure all members have joined the GitHub group.
  

If You Have Extra Time

• Update guidance.py to handle horizontal as well as vertical control. Your finished control node should reliably move the rocket to whatever point the user clicks in the simulator window.