Robotics Design Patterns

When to Use This Skill

• Designing robot software architecture from scratch
• Choosing between behavior trees, FSMs, or hybrid approaches
• Structuring perception → planning → control pipelines
• Implementing safety systems and watchdogs
• Building hardware abstraction layers (HAL)
• Designing for sim-to-real transfer
• Architecting multi-robot / fleet systems
• Making real-time vs. non-real-time tradeoffs

Pattern 1: The Robot Software Stack

Every robot system follows this layered architecture, regardless of complexity:

┌─────────────────────────────────────────────┐
│               APPLICATION LAYER              │
│    Mission planning, task allocation, UI     │
├─────────────────────────────────────────────┤
│              BEHAVIORAL LAYER                │
│  Behavior trees, FSMs, decision-making       │
├─────────────────────────────────────────────┤
│             FUNCTIONAL LAYER                 │
│  Perception, Planning, Control, Estimation   │
├─────────────────────────────────────────────┤
│           COMMUNICATION LAYER                │
│     ROS2, DDS, shared memory, IPC            │
├─────────────────────────────────────────────┤
│          HARDWARE ABSTRACTION LAYER          │
│    Drivers, sensor interfaces, actuators     │
├─────────────────────────────────────────────┤
│              HARDWARE LAYER                  │
│    Cameras, LiDARs, motors, grippers, IMUs   │
└─────────────────────────────────────────────┘

Design Rule: Information flows UP through perception, decisions flow DOWN through control. Never let the application layer directly command hardware.

Pattern 2: Behavior Trees (BT)

Behavior trees are the recommended default for robot decision-making. They're modular, reusable, and easier to debug than FSMs for complex behaviors.

Core Node Types

Sequence (→)     : Execute children left-to-right, FAIL on first failure
Fallback (?)     : Execute children left-to-right, SUCCEED on first success
Parallel (⇉)     : Execute all children simultaneously
Decorator        : Modify a single child's behavior
Action (leaf)    : Execute a robot action
Condition (leaf) : Check a condition (no side effects)

Example: Pick-and-Place BT

                    → Sequence
                   /    |      \
            → Check     → Pick     → Place
           /    \      /   |  \     /  |  \
       Battery  Obj  Open  Move  Close Move Open Release
       OK?    Found? Grip  To
(截断)