Behaviour Trees in Robotics — Complete Guide
178 words · 1 min read
Behaviour trees are a hierarchical decision-making structure that lets robots compose complex behaviour from reusable building blocks. Replacing state machines in modern robotics.
The concept concept: Behaviour trees are a hierarchical decision-making structure that
Difficulty 3/5 · ClassroomA behaviour tree (BT) is a hierarchical tree of decision nodes that controls what a robot should do moment to moment. Originally invented for video-game AI, BTs are now standard in modern robotics — including Nav2 and MoveIt2.
💡 Think of it like…
Think of it like a household object that does the same job — the underlying idea is the same, just adapted for robots.
Why it matters
Without behaviour trees in robotics — complete guide, many concept systems in robotics simply couldn't work.
Behaviour Trees in Robotics
What is it?
A behaviour tree (BT) is a hierarchical tree of decision nodes that controls what a robot should do moment to moment. Originally invented for video-game AI, BTs are now standard in modern robotics — including Nav2 and MoveIt2.
How it works
A BT is composed of control-flow nodes (Sequence, Selector, Parallel) and leaf nodes (Action, Condition). On each tick, the root ticks its children, and so on, evaluating until a SUCCESS, FAILURE, or RUNNING result returns. Sequences fail on first FAILURE; Selectors succeed on first SUCCESS. This composability lets engineers build complex behaviour from a few reusable primitives.
Real-world example
Nav2's bt_navigator runs the entire navigation stack as a behaviour tree. Many warehouse robots use BTs to switch between picking, transporting, charging, and recovering from failures.
Why it matters for robotics
Behaviour trees are far more readable and maintainable than nested if-else logic or large state machines. Any robotics engineer working on Nav2 today is expected to know BTs.
See also
Ask R2 Co-pilot anything you didn't understand about Behaviour Trees in Robotics — Complete Guide. It'll explain it plainly.
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Last updated · 2026-05-21
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