Action Nodes
Action nodes send ROS topic messages from the behavior tree to the robot.
Often the type of message sent from an Action node is a cmd_vel message which encodes movement instructions for the robot.
Update Nodes
Update nodes are designated for updating data in the blackboard.
Often times the types of data updates performed by Update nodes include preprocessing or processing of message data from the robot.
Conditional Nodes
Conditional nodes will return either "success" or "failure", corresponding to the boolean values "true" and "false" respectively
Conditional nodes will access data in the blackboard and return one of the two values listed above based on if a particular condition is met within the data.