patrol-behavior-tree

Define a main tree with a ReactiveFallback for mission priorities, a PatrolLoop subtree using KeepRunningUntilFailure over waypoint subtrees, and a NavigateWithRecovery subtree wrapping plan, smooth, and follow actions in a Retry decorator.

Place an IsBatteryLow condition inside a ReactiveSequence at the top of a ReactiveFallback so it is re-evaluated every tick. Use two thresholds, such as 10% for emergency preemption and 20% for graceful patrol interruption.

ReactiveSequence re-ticks all preceding conditions and halts running children if one fails, while ReactiveFallback re-evaluates children in priority order and returns the first success. The patrol tree uses ReactiveFallback so battery emergencies preempt all other behaviors.

Yes, it uses standard Nav2 BT action nodes such as ComputePathToPose, SmoothPath, FollowPath, and IsPathValid with their server names. Waypoints are injected into the blackboard from a YAML parameter file in the BT navigator configuration.

The Retry decorator is configured with 3 attempts, so after three failures the subtree returns FAILURE and the patrol moves on or the loop stops. Increase num_attempts or add a recovery subtree if transient obstacles cause frequent failures.