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Writing a new controller
In this framework controllers are libraries, dynamically loaded by the controller manager using the pluginlib interface. The following is a step-by-step guide to create source files, basic tests, and compile rules for a new controller.
If the package for the controller does not exist, then create it first. The package should have
ament_cmakeas a build type. The easiest way is to search online for the most recent manual. A helpful command to support this process is
ros2 pkg create. Use the
--helpflag for more information on how to use it. There is also an option to create library source files and compile rules to help you in the following steps.
Preparing source files
After creating the package, you should have at least
package.xmlfiles in it. Create also
srcfolders if they do not already exist. In
srcfolder. Optionally add
visibility_control.hwith the definition of export rules for Windows. You can copy this file from an existing controller package and change the name prefix to the
Adding declarations into header file (.hpp)
Take care that you use header guards. ROS2-style is using
#definepreprocessor directives. (For more information on this, a search engine is your friend :) ).
visibility_control.hif you are using one.
Define a unique namespace for your controller. This is usually a package name written in
Define the class of the controller, extending
ControllerInterface, e.g., .. code:: c++ class ControllerName : public controller_interface::ControllerInterface
Add a constructor without parameters and the following public methods overriding the
update. For exact definitions check the
controller_interface/controller_interface.hppheader or one of the controllers from ros2_controllers.
(optional) Often, controllers accept lists of joint names and interface names as parameters. If so, you can add two protected string vectors to store those values.
Adding definitions into source file (.cpp)
Include the header file of your controller and add a namespace definition to simplify further development.
(optional) Implement a constructor if needed. There, you could initialize member variables. This could also be done in the
initmethod. The first line usually calls the parent
initmethod. Here is the best place to initialize the variables, reserve memory, and most importantly, declare node parameters used by the controller. If everything works fine return
on_configuremethod. Parameters are usually read here, and everything is prepared so that the controller can be started.
state_interface_configurationwhere required interfaces are defined. There are three options of the interface configuration
NONEoption will ask for access to all available interfaces or none of them. The
INDIVIDUALconfiguration needs a detailed list of required interface names. Those are usually provided as parameters. The full interface names have structure
on_activatemethod with checking, and potentially sorting, the interfaces and assigning members’ initial values. This method is part of the real-time loop, therefore avoid any reservation of memory and, in general, keep it as short as possible.
on_deactivatemethod, which does the opposite of
on_activate. In many cases, this method is empty. This method should also be real-time safe as much as possible.
updatemethod as the main entry point. The method should be implemented with real-time constraints in mind. When this method is called, the state interfaces have the most recent values from the hardware, and new commands for the hardware should be written into command interfaces.
IMPORTANT: At the end of your file after the namespace is closed, add the
PLUGINLIB_EXPORT_CLASSmacro. For this you will need to include the
"pluginlib/class_list_macros.hpp"header. As first parameters you should provide exact controller class, e.g.,
<controller_name_namespace>::<ControllerName>, and as second the base class, i.e.,
Writing export definition for pluginlib
<controller_name>.xmlfile in the package and add a definition of the library and controller’s class which has to be visible for the pluginlib. The easiest way to do that is to check other controllers in the ros2_controllers package.
Usually, the plugin name is defined by the package (namespace) and the class name, e.g.,
<controller_name_package>/<ControllerName>. This name defines the controller’s type when the controller manager searches for it. The other two parameters have to correspond to the definition done in macro at the bottom of the
Writing simple test to check if the controller can be found and loaded
Create the folder
testin your package, if it does not exist already, and add a file named
You can safely copy the file’s content for any controller defined in the ros2_controllers package.
Change the name of the copied test and in the last line, where controller type is specified put the name defined in
Add compile directives into ``CMakeLists.txt`` file
Under the line
find_package(ament_cmake REQUIRED)add further dependencies. Those are at least:
Add a compile directive for a shared library providing the
<controller_name>.cppfile as the source.
Add targeted include directories for the library. This is usually only
Add ament dependencies needed by the library. You should add at least those listed under 1.
Export for pluginlib description file using the following command: .. code:: cmake
Add install directives for targets and include directory.
In the test section add the following dependencies:
Add compile definitions for the tests using the
ament_add_gmockdirective. For details, see how it is done for controllers in the ros2_controllers package.
(optional) Add your controller`s library into
Add dependencies into ``package.xml`` file
Add at least the following packages into
Add at least the following package into
Compiling and testing the controller
Now everything is ready to compile the controller using the
colcon build <controller_name_package>command. Remember to go into the root of your workspace before executing this command.
If compilation was successful, source the
setup.bashfile from the install folder and execute
colcon test <controller_name_package>to check if the new controller can be found through
pluginliblibrary and be loaded by the controller manager.
That’s it! Enjoy writing great controllers!