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Pendulum demo design

Purpose

This is a rework of the existing pendulum demo in ros2/demos. The aim of this project is to create a complete use case to show ROS 2 real-time capabilities. The goal is not measure ROS 2 real-time performance but to show how ROS 2 could be used for a real-time application. Ideally this project could help ROS developers to understand how to program a ROS 2 application in C ++, which ROS 2 features could be used, how to configure the process and how to instrument the application to verify the real-time capabilities.

Managed nodes

The main nodes used in the demo /pendulum_controller and /pendulum_driver are managed nodes. They inherit from a Lifecycle node and it is possible to control the node state. All the configurations and dynamic memory allocation must be done before entering to the Active tate, for example in the onConfigure transition.

lifecycle_rt

The image above was taken from Jackie Kay's Roscon keynote in 2015.

Component overview

  • PendulumControllerNode: Class derived from LifecycleNode that implements the ROS 2 interface for the pendulum controller.
  • PendulumController: A controller implementation based on a full state feedback controller.
  • PendulumDriverNode: Class derived from LifecycleNode that implements the ROS 2 interface for a simulated pendulum.
  • PendulumDriver: A class which implements a simulation of a cart-pole based pendulum.
  • pendulum_demo: The main program which configures the process settings, creates and executor , adds a PendulumControllerNode and a PendulumDriverNode using manual composition and spins all the nodes.