This is a ROS2 package providing the base class for all actuator drivers and the interface for all modules looking to interact with actuators.
Most actuator drivers need to be integrated with ros2_control using hardware_interface.
This package is used by
remote_hardware_interface for position or velocity control.
So all drivers using remote_actuator as the base class become integrated
with ros2_control automatically.
The actuator drivers implement the base class provided by this package.
For C++ drivers, that means that they use
remote_actuator::Implementation as a parent class.
Its constructor requires an instance of rclcpp::Node to read the
parameters from.
The following methods need to be implemented by each driver:
public:
/* has_position must return true if it supports position control */
virtual bool has_position() override;
/* has_velocity must return true if it supports velocity control */
virtual bool has_velocity() override;
protected:
/* position_set_real_ is called to control the position */
virtual void position_set_real_(double) override;
/* velocity_set_real_ is called to control the velocity */
virtual void velocity_set_real_(double) override;The users can chose one of three ways to interact with child classes of remote_actuator::Implementation:
-
Link with the driver directly to make native API calls:
auto actuator = \ std::make_shared<driver_package::DriverClass>(node, "/motor1"); actuator->set_position(0.0); actuator->set_veloicty(1.0);
In this case the driver is running within the same process and it is destroyed when the
actuatorobject is destroyed. -
Link with
remote_actuatorto make ROS2 interface (DDS) calls (locally or over a network):auto actuator = \ std::make_shared<remote_actuator::RemoteInterface>(node, "/motor1"); actuator->set_position(0.0); actuator->set_veloicty(1.0);
In this case the driver can be elsewhere within DDS' reach (same process or another side of the globe).
-
Let the runtime make the choice between the above two options:
auto actuator = \ remote_actuator::Factory::New(node, "/motor1"); // or auto actuator = \ driver_package::Factory::New(node, "/motor1");
In this case the boolean value of the parameter
actuator_is_remotedetermines whether the driver is instantiated locally or if a remote interface is used to reach the driver instantiated elsewhere. Please, note, the trivial classdriver_package::Factory(similar toremote_actuator::Factory) has to be written to support this use case.
No matter which option is chosen, the driver will expose the following ROS2 interfaces.
actuator_prefix: the prefix to ROS2 interfaces exposed by this driver- Minimum and maximum values for filtering input as well as to support logic in other related modules (e.g. for PWM control):
actuator_position_minandactuator_position_maxfor position controlled actuatorsactuator_velocity_minandactuator_velocity_maxfor position controlled actuators
actuator_is_remote: instructs the factory class (if any) whether to instantiate the driver locally or to connect to a remote instance
<namespace>/<actuator_prefix>/set_position: set the position<namespace>/<actuator_prefix>/set_velocity: set the velocity
<namespace>/<actuator_prefix>/position: the last position<namespace>/<actuator_prefix>/velocity: the last velocity
<namespace>/<actuator_prefix>/set_position: set the position<namespace>/<actuator_prefix>/set_velocity: set the velocity
See em2rs_driver for an example of a driver that implements
remote_actuator.