Controller Creation Tutorial

This tutorial describes how to make a new controller.

The contents of this page include:

Overview

Controller are used to bridge the gap between a libgazebo interface and the phyiscal attributes of a model. Essentially, controllers are meant to move joints, read commands from libgazebo, and write data to libgazebo.

When creating a new robot or sensor, first check the available controllers. Sometimes a pre-existing controller will suit your needs. For example, a new type of camera could potentially use the generic_camera controller. Or if a new robot has a drive train similar to a Pioneer2dx, then use the pioneer2dx_position2d controller.

Initial Construction

The first step it to decide where in the code base to place your new controller. Camera controllers should go in the camera directory, gazebo/server/controllers/camera, and 2d position controllers should go in gazebo/server/controller/position2d. Create a new directory as appropriate.

Copy the example controller, gazebo/server/controler/ControllerStub.* to your new controller directory. Replace the names as appropriate.

Load the Controller

This section deals with the LoadChild function, which is called after initial creationg of the controller.

A controller should have one or more interfaces. Make sure to get a valid pointer to the controllers inteface.

If we are creating a position2d controller, this code would be:

this->myIface = dynamic_cast<PositionIface*>(this->ifaces[0]);

if (!this->myIface)
  gzthrow("NAME controller requires a PositionIface");

Use the XMLConfigNode pointer to load in any other necessary parameters. For example, the Pioneer2d_Position controller need two hinge joints:

std::string leftJointName = node->GetString("leftJoint", "", 1);
std::string rightJointName = node->GetString("rightJoint", "", 1);

this->joints[LEFT] = dynamic_cast<HingeJoint*>(this->myParent->GetJoint(leftJointName));
this->joints[RIGHT] = dynamic_cast<HingeJoint*>(this->myParent->GetJoint(rightJointName));

if (!this->joints[LEFT])
  gzthrow("couldn't get left hinge joint");

if (!this->joints[RIGHT])
  gzthrow("couldn't get right hinge joint");

Intialize the Controller

After the controller is loaded, the InitChild function is called. Use this function to initialize any variables.

The Update Function

Once every interation the UpdateChild function is called. Use this function to get command from the libgazebo interface, manipulate any physical objects, and publish new data.

For a good example of manipulating joints, look at the Pioneer2dx_Position2d controller. For a a good example of publishing data, look at the SickLMS200_Laser controller.