jetson/ros2_ws/src/saltybot_cliff_detector/config/cliff_detector_config.yaml

@@ -0,0 +1,12 @@
+cliff_detector:
+  ros__parameters:
+    # Cliff threshold in meters (readings > this = drop-off)
+    cliff_threshold: 0.5
+
+    # Number of consecutive detections before triggering
+    # (debouncing to avoid false positives)
+    debounce_count: 3
+
+    # Minimum number of sensors that must exceed threshold
+    # (majority voting for robustness)
+    min_sensors: 2

jetson/ros2_ws/src/saltybot_cliff_detector/launch/cliff_detector.launch.py

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+"""Launch file for cliff detector node."""
+
+from launch import LaunchDescription
+from launch_ros.actions import Node
+from launch.substitutions import LaunchConfiguration
+from launch.actions import DeclareLaunchArgument
+import os
+from ament_index_python.packages import get_package_share_directory
+
+
+def generate_launch_description():
+    """Generate launch description for cliff detector."""
+    pkg_dir = get_package_share_directory("saltybot_cliff_detector")
+    config_file = os.path.join(pkg_dir, "config", "cliff_detector_config.yaml")
+
+    return LaunchDescription(
+        [
+            DeclareLaunchArgument(
+                "config_file",
+                default_value=config_file,
+                description="Path to configuration YAML file",
+            ),
+            Node(
+                package="saltybot_cliff_detector",
+                executable="cliff_detector_node",
+                name="cliff_detector",
+                output="screen",
+                parameters=[LaunchConfiguration("config_file")],
+            ),
+        ]
+    )

jetson/ros2_ws/src/saltybot_cliff_detector/package.xml

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+<?xml version="1.0"?>
+<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
+<package format="3">
+  <name>saltybot_cliff_detector</name>
+  <version>0.1.0</version>
+  <description>Cliff and drop-off detection safety node for SaltyBot</description>
+  <maintainer email="sl-controls@saltylab.local">SaltyLab Controls</maintainer>
+  <license>MIT</license>
+
+  <buildtool_depend>ament_python</buildtool_depend>
+  <depend>rclpy</depend>
+  <depend>sensor_msgs</depend>
+  <depend>std_msgs</depend>
+
+  <test_depend>pytest</test_depend>
+  <test_depend>std_msgs</test_depend>
+
+  <export>
+    <build_type>ament_python</build_type>
+  </export>
+</package>

jetson/ros2_ws/src/saltybot_cliff_detector/saltybot_cliff_detector/cliff_detector_node.py

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+#!/usr/bin/env python3
+"""Cliff and drop-off detection node for SaltyBot.
+
+Monitors downward-facing IR range sensors for drop-offs/stair edges.
+Triggers emergency stop when any sensor reading exceeds threshold.
+
+Subscribed topics:
+  /saltybot/cliff_sensors (sensor_msgs/LaserScan) - IR range array
+
+Published topics:
+  /saltybot/cliff_detected (std_msgs/Bool) - Cliff/drop-off detected
+"""
+
+import rclpy
+from rclpy.node import Node
+from sensor_msgs.msg import LaserScan
+from std_msgs.msg import Bool
+
+
+class CliffDetectorNode(Node):
+    """ROS2 node for cliff and drop-off detection."""
+
+    def __init__(self):
+        super().__init__("cliff_detector")
+
+        # Parameters
+        self.declare_parameter("cliff_threshold", 0.5)
+        self.declare_parameter("debounce_count", 3)
+        self.declare_parameter("min_sensors", 2)
+
+        self.cliff_threshold = self.get_parameter("cliff_threshold").value
+        self.debounce_count = self.get_parameter("debounce_count").value
+        self.min_sensors = self.get_parameter("min_sensors").value
+
+        # State tracking
+        self.cliff_detected = False
+        self.consecutive_detections = 0
+
+        # Subscription to cliff sensors
+        self.sub_cliff = self.create_subscription(
+            LaserScan, "/saltybot/cliff_sensors", self._on_cliff_sensors, 10
+        )
+
+        # Publisher for cliff detection
+        self.pub_cliff = self.create_publisher(Bool, "/saltybot/cliff_detected", 10)
+
+        self.get_logger().info(
+            f"Cliff detector initialized. "
+            f"Threshold: {self.cliff_threshold}m, "
+            f"Debounce: {self.debounce_count} frames, "
+            f"Min sensors: {self.min_sensors}"
+        )
+
+    def _on_cliff_sensors(self, msg: LaserScan) -> None:
+        """Process cliff sensor readings."""
+        # Filter out NaN/inf values and check against threshold
+        valid_ranges = [r for r in msg.ranges if 0 < r < float('inf')]
+
+        if len(valid_ranges) == 0:
+            # No valid readings - assume safe
+            self._update_cliff_state(False)
+            return
+
+        # Count how many sensors exceed threshold
+        exceeding_sensors = sum(1 for r in valid_ranges if r > self.cliff_threshold)
+
+        # Cliff detected if min_sensors or more exceed threshold
+        cliff_detected_now = exceeding_sensors >= self.min_sensors
+
+        if cliff_detected_now:
+            self.consecutive_detections += 1
+            if self.consecutive_detections >= self.debounce_count:
+                self._update_cliff_state(True)
+        else:
+            self.consecutive_detections = 0
+            self._update_cliff_state(False)
+
+    def _update_cliff_state(self, detected: bool) -> None:
+        """Update cliff state and publish."""
+        if detected != self.cliff_detected:
+            self.cliff_detected = detected
+            if detected:
+                self.get_logger().warn("CLIFF DETECTED! Emergency stop triggered!")
+            else:
+                self.get_logger().info("Cliff cleared, continuing operation")
+
+        # Always publish current state
+        msg = Bool(data=self.cliff_detected)
+        self.pub_cliff.publish(msg)
+
+
+def main(args=None):
+    rclpy.init(args=args)
+    node = CliffDetectorNode()
+    try:
+        rclpy.spin(node)
+    except KeyboardInterrupt:
+        pass
+    finally:
+        node.destroy_node()
+        rclpy.shutdown()
+
+
+if __name__ == "__main__":
+    main()

jetson/ros2_ws/src/saltybot_cliff_detector/setup.cfg

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+[develop]
+script_dir=$base/lib/saltybot_cliff_detector
+
+[install]
+install_scripts=$base/lib/saltybot_cliff_detector

jetson/ros2_ws/src/saltybot_cliff_detector/setup.py

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+from setuptools import setup, find_packages
+
+setup(
+    name='saltybot_cliff_detector',
+    version='0.1.0',
+    packages=find_packages(),
+    data_files=[
+        ('share/ament_index/resource_index/packages', ['resource/saltybot_cliff_detector']),
+        ('share/saltybot_cliff_detector', ['package.xml']),
+        ('share/saltybot_cliff_detector/config', ['config/cliff_detector_config.yaml']),
+        ('share/saltybot_cliff_detector/launch', ['launch/cliff_detector.launch.py']),
+    ],
+    install_requires=['setuptools'],
+    zip_safe=True,
+    author='SaltyLab Controls',
+    author_email='sl-controls@saltylab.local',
+    description='Cliff and drop-off detection safety node for SaltyBot',
+    license='MIT',
+    entry_points={
+        'console_scripts': [
+            'cliff_detector_node=saltybot_cliff_detector.cliff_detector_node:main',
+        ],
+    },
+)

jetson/ros2_ws/src/saltybot_cliff_detector/test/test_cliff_detector.py

@@ -0,0 +1,205 @@
+"""Tests for cliff detector node."""
+
+import pytest
+from sensor_msgs.msg import LaserScan
+from std_msgs.msg import Bool
+import rclpy
+
+from saltybot_cliff_detector.cliff_detector_node import CliffDetectorNode
+
+
+@pytest.fixture
+def rclpy_fixture():
+    rclpy.init()
+    yield
+    rclpy.shutdown()
+
+
+@pytest.fixture
+def node(rclpy_fixture):
+    node = CliffDetectorNode()
+    yield node
+    node.destroy_node()
+
+
+class TestInit:
+    def test_node_initialization(self, node):
+        assert node.cliff_threshold == 0.5
+        assert node.debounce_count == 3
+        assert node.min_sensors == 2
+        assert node.cliff_detected is False
+        assert node.consecutive_detections == 0
+
+
+class TestCliffDetection:
+    def test_cliff_threshold_exceeded(self, node):
+        """Test detection when sensor exceeds threshold."""
+        msg = LaserScan()
+        msg.ranges = [0.3, 0.6, 0.4]  # 1 sensor exceeds threshold
+
+        node._on_cliff_sensors(msg)
+        assert node.consecutive_detections == 1
+
+    def test_multiple_sensors_exceed(self, node):
+        """Test detection with multiple sensors exceeding threshold."""
+        msg = LaserScan()
+        msg.ranges = [0.6, 0.7, 0.4]  # 2 sensors exceed threshold
+
+        node._on_cliff_sensors(msg)
+        assert node.consecutive_detections == 1
+
+    def test_debounce_threshold(self, node):
+        """Test debouncing requires multiple consecutive detections."""
+        node.cliff_threshold = 0.5
+        node.debounce_count = 3
+        node.min_sensors = 1
+
+        msg = LaserScan()
+        msg.ranges = [0.6, 0.3, 0.4]  # 1 exceeds
+
+        # First detection
+        node._on_cliff_sensors(msg)
+        assert node.cliff_detected is False
+        assert node.consecutive_detections == 1
+
+        # Second detection
+        node._on_cliff_sensors(msg)
+        assert node.cliff_detected is False
+        assert node.consecutive_detections == 2
+
+        # Third detection - should trigger
+        node._on_cliff_sensors(msg)
+        assert node.cliff_detected is True
+        assert node.consecutive_detections == 3
+
+    def test_debounce_reset_on_clear(self, node):
+        """Test debounce counter resets when cliff clears."""
+        node.debounce_count = 2
+        node.min_sensors = 1
+
+        msg_cliff = LaserScan()
+        msg_cliff.ranges = [0.6, 0.3]
+
+        msg_clear = LaserScan()
+        msg_clear.ranges = [0.3, 0.2]
+
+        # Detection
+        node._on_cliff_sensors(msg_cliff)
+        assert node.consecutive_detections == 1
+
+        # Clear
+        node._on_cliff_sensors(msg_clear)
+        assert node.consecutive_detections == 0
+        assert node.cliff_detected is False
+
+    def test_min_sensors_voting(self, node):
+        """Test minimum sensor threshold (majority voting)."""
+        node.min_sensors = 2
+        node.debounce_count = 1
+
+        msg = LaserScan()
+        msg.ranges = [0.6, 0.3, 0.4]  # Only 1 exceeds
+
+        node._on_cliff_sensors(msg)
+        assert node.cliff_detected is False
+
+        msg.ranges = [0.6, 0.7, 0.4]  # 2 exceed
+        node._on_cliff_sensors(msg)
+        assert node.cliff_detected is True
+
+    def test_nan_values_filtered(self, node):
+        """Test that NaN/inf values are filtered out."""
+        node.debounce_count = 1
+        node.min_sensors = 1
+
+        msg = LaserScan()
+        msg.ranges = [float('nan'), 0.6, float('inf')]
+
+        node._on_cliff_sensors(msg)
+        # Only 0.6 is valid and exceeds threshold
+        assert node.cliff_detected is True
+
+    def test_empty_ranges(self, node):
+        """Test behavior with empty or all-invalid ranges."""
+        msg = LaserScan()
+        msg.ranges = []
+
+        node._on_cliff_sensors(msg)
+        assert node.cliff_detected is False
+
+        msg.ranges = [float('nan'), float('inf')]
+        node._on_cliff_sensors(msg)
+        assert node.cliff_detected is False
+
+
+class TestStateTransitions:
+    def test_cliff_to_clear_transition(self, node):
+        """Test state transition from cliff to clear."""
+        node.debounce_count = 1
+        node.min_sensors = 1
+
+        # Trigger cliff
+        msg_cliff = LaserScan()
+        msg_cliff.ranges = [0.6, 0.3]
+        node._on_cliff_sensors(msg_cliff)
+
+        assert node.cliff_detected is True
+
+        # Clear cliff
+        msg_clear = LaserScan()
+        msg_clear.ranges = [0.3, 0.2]
+        node._on_cliff_sensors(msg_clear)
+
+        assert node.cliff_detected is False
+
+    def test_clear_to_cliff_transition(self, node):
+        """Test state transition from clear to cliff."""
+        node.debounce_count = 1
+        node.min_sensors = 1
+
+        # Start clear
+        assert node.cliff_detected is False
+
+        # Trigger cliff
+        msg_cliff = LaserScan()
+        msg_cliff.ranges = [0.6, 0.3]
+        node._on_cliff_sensors(msg_cliff)
+
+        assert node.cliff_detected is True
+
+
+class TestEdgeCases:
+    def test_single_sensor_exceeds(self, node):
+        """Test with single sensor exceeding threshold."""
+        node.min_sensors = 1
+        node.debounce_count = 1
+
+        msg = LaserScan()
+        msg.ranges = [0.6]
+
+        node._on_cliff_sensors(msg)
+        assert node.cliff_detected is True
+
+    def test_zero_readings(self, node):
+        """Test that zero readings are filtered (invalid)."""
+        msg = LaserScan()
+        msg.ranges = [0.0, 0.6, 0.0]  # Only 0.6 is valid
+
+        node._on_cliff_sensors(msg)
+        # 0.6 exceeds 0.5, but need 2 sensors with min_sensors=2
+        assert node.cliff_detected is False
+
+    def test_threshold_boundary(self, node):
+        """Test boundary condition at exact threshold."""
+        node.debounce_count = 1
+        node.min_sensors = 1
+
+        msg = LaserScan()
+        msg.ranges = [0.5, 0.3]  # Exactly at threshold (not exceeding)
+
+        node._on_cliff_sensors(msg)
+        assert node.cliff_detected is False
+
+        msg.ranges = [0.50001, 0.3]  # Just above threshold
+        node._on_cliff_sensors(msg)
+        assert node.cliff_detected is True