(ROS Specific) Implementing Reactive Fallback

[martijnhabers]

What would be the best way to implement a reactive fallback with ROS Actions to continuously check for a condition?

Take this example:

• Fallback
  ----> IsAligned
  ----> AlignRobot

IsAligned checks if the robot is aligned w.r.t a wall, if it is not, AlignRobot aligns it to said wall. However, AlignRobot does not have ability to check completion of task so it will just loop indefinitely.

Currently, IsAligned is a ROSActionNode which calls the ROS IsAligned Action. However, making this Fallback a ReactiveFallback would mean IsAligned would be ticked at a frequency which is not ideal for ROS to call the ROS action (since ROS actions are not really designed for this).

My idea is to have a ROS node in the background constantly checking alignment and it somehow setting a blackboard value which can then be checked with a BT::ConditionNode.

Is this something that would be possible?