control_toolbox_pid_tutorial

I found myself with some difficulties to understand how to use the control_toolbox::pid class. After struggling to make it work, here I share my findings with a tutorial package to get you set up!

First, docs from the Pid class: http://docs.ros.org/api/control_toolbox/html/classcontrol__toolbox_1_1Pid.html

Mainly the interesting bits of this package are in src/example.cpp.

It implements a pid controller for a made up geometry_msgs/Twist cmd_vel. There is nothing to actually control for real, but you can play with the parts and find a working pid implementation with dynamic reconfigure to tune it available.

You should be able to build this package with something like:

mkdir -p pid_ws/src
cd pid_ws/src
git clone https://github.com/awesomebytes/control_toolbox_pid_tutorial
cd ..
catkin build
source devel/setup.bash

You can run the example node with:

rosrun control_toolbox_pid_tutorial pid_example

Or check it out with a launchfile setting up the PID parameters:

roslaunch control_toolbox_pid_tutorial example.launch

Dynamic reconfigure

Looks like this:

PID state topic

If before starting the node that contains the PID you set the parameter publish_state in the param server to true, you'll get access to the PID internal state.

$ rostopic echo /my_namespace/my_pid/state
header: 
  seq: 992
  stamp: 
    secs: 1545405985
    nsecs: 449541433
  frame_id: ''
timestep: 
  secs: 0
  nsecs: 100291320
error: 0.0
error_dot: 0.0
p_error: 0.0
i_error: 0.0
d_error: 0.0
p_term: 0.0
i_term: 0.0
d_term: 0.0
i_max: 10.0
i_min: -10.0
output: 0.0
---

Debug all together

In my case, to debug what is going on I use:

rosrun rqt_robot_steering rqt_robot_steering (or rqt adding the plugin) to send geometry_msgs/Twist commands to a topic.
rosrun rqt_reconfigure rqt_reconfigure (or rqt adding the plugin) to play with the PID gains.
rosrun plotjuggler PlotJuggler PlotJuggler to visualize in real time the different inputs and outputs, including the PID state, in case that helps debugging (it may help to choose i_clamp values of the PID). rqt_multiplot could be used too (as rqt plugin probably).
Some rostopic echo of the topics that come in and out. They are useful sometimes too.
rosbag record and rosbag play to check in an offline fashion.

Stuff you may need installed

sudo apt-get install ros-kinetic-control-toolbox ros-kinetic-rqt-reconfigure ros-kinetic-plotjuggler ros-kinetic-rqt-robot-steering

But chances are you already have them.

awesomebytes / control_toolbox_pid_tutorial Goto Github PK