Components

A Component is the main execution unit, every Component is equivalent to a ROS2 Lifecycle Node comprising of:

• Input and Outputs

• Health Status

• Fallbacks

Component Structure

Each Component must serve one main functionality which can be executed in different modes or ComponentRunType (Example below), additionally the Component can offer any number of additional services.

Available ComponentRunType are:

RunType (str)	RunType (enum)	Description
Timed	ComponentRunType.TIMED	Executes main functionality in a timed loop while active
Event	ComponentRunType.EVENT	Executes main functionality based on a trigger topic/event
Server	ComponentRunType.SERVER	Executes main functionality based on a ROS2 service request from a client
ActionServer	ComponentRunType.ACTIONSERVER	Executes main functionality based on a ROS2 action server request from a client

The run type can be configured using ‘run_type’ attribute in the component config class, or directly using ‘run_type’ property:

from ros_sugar.config import ComponentRunType, BaseComponentConfig
from ros_sugar.core import BaseComponent

config = BaseComponentConfig(run_type=ComponentRunType.EVENT)

# Can directly pass a string
config = ComponentConfig(run_type="Event")

# Can set from Component
comp = BaseComponent(component_name='test')
comp.run_type = "Server"    # or ComponentRunType.SERVER

Tip

All the functionalities implemented in ROS2 nodes can be found in the Component.

Inputs and Outputs

Each component can be configured with a set of input topics and output topics. When launched the component will automatically create ROS2 subscribers, publishers and callbacks to the associated inputs/outputs.

from ros_sugar.core import BaseComponent
from ros_sugar.io import Topic

# Define a set of topics
map_topic = Topic(name="map", msg_type="OccupancyGrid")
audio_topic = Topic(name="voice", msg_type="Audio")
image_topic = Topic(name="camera/rgb", msg_type="Image")

# Init the component with inputs/outputs
comp = BaseComponent(component_name='test', inputs=[map_topic, image_topic], outputs=[audio_topic])

See also

Check how to configure a topic for the component input or output here

Health Status

Each Component comes with an associated health status to express the well or mal-function of the component. Health status is always available internally and can in the component by associating failure status to a Fallback behavior allowing the component to self-recover. Component also have the option to declare the status back to the system by publishing on a Topic. This can be configured in the BaseComponentConfig class.

Learn more on using health status in the component here.

Fallbacks

Component fallbacks are aet of techniques to be applied internally in case of failure to allow self-recovery within the component. Check the fallbacks dedicated page to learn how to use and configure your own fallbacks.