feat: Add battery-aware speed limiter ROS2 node (Issue #321)

Implements saltybot_battery_speed_limiter package:
- Subscribes to /saltybot/battery_state, publishes speed limit factor
- Battery percentage thresholds: 100-50%=1.0, 50-25%=0.7, 25-15%=0.4, <15%=0.0
- Reduces speed to preserve battery when running low
- Automatically stops movement below 15% to prevent deep discharge
- Configurable thresholds and speed factors
- Comprehensive test suite: 30+ tests covering all threshold transitions
- Handles both direct percentage and voltage-based fallback calculation

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

jetson/ros2_ws/src/saltybot_battery_speed_limiter/config/battery_limiter_config.yaml

@@ -0,0 +1,23 @@
+# Battery Speed Limiter Configuration
+battery_speed_limiter:
+  ros__parameters:
+    # Battery percentage thresholds
+    threshold_full_1: 100    # Upper bound for full speed
+    threshold_full_2: 50     # Lower bound for full speed
+    threshold_reduced_1: 50  # Upper bound for reduced speed
+    threshold_reduced_2: 25  # Lower bound for reduced speed
+    threshold_critical_1: 25 # Upper bound for critical speed
+    threshold_critical_2: 15 # Lower bound for critical speed
+    threshold_stop: 15       # Below this: stop
+
+    # Speed limit factors
+    speed_factor_full: 1.0      # 100-50%: full speed
+    speed_factor_reduced: 0.7   # 50-25%: 70% speed
+    speed_factor_critical: 0.4  # 25-15%: 40% speed
+    speed_factor_stop: 0.0      # <15%: stop
+
+    # Publishing frequency (Hz)
+    publish_frequency: 10
+
+    # Enable/disable limiting
+    enable_limiting: true

jetson/ros2_ws/src/saltybot_battery_speed_limiter/launch/battery_speed_limiter.launch.py

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+import os
+from launch import LaunchDescription
+from launch_ros.actions import Node
+from launch_ros.substitutions import FindPackageShare
+from launch.substitutions import PathJoinSubstitution
+
+
+def generate_launch_description():
+    config_dir = PathJoinSubstitution(
+        [FindPackageShare('saltybot_battery_speed_limiter'), 'config']
+    )
+    config_file = PathJoinSubstitution([config_dir, 'battery_limiter_config.yaml'])
+
+    battery_limiter = Node(
+        package='saltybot_battery_speed_limiter',
+        executable='battery_speed_limiter_node',
+        name='battery_speed_limiter',
+        output='screen',
+        parameters=[config_file],
+        remappings=[
+            ('/saltybot/battery_state', '/saltybot/battery_state'),
+            ('/saltybot/speed_limit_factor', '/saltybot/speed_limit_factor'),
+        ],
+    )
+
+    return LaunchDescription([
+        battery_limiter,
+    ])

jetson/ros2_ws/src/saltybot_battery_speed_limiter/package.xml

@@ -0,0 +1,28 @@
+<?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_battery_speed_limiter</name>
+  <version>0.1.0</version>
+  <description>Battery-aware speed limiter that adjusts robot speed based on battery state to preserve charge</description>
+
+  <maintainer email="sl-controls@saltybot.local">SaltyBot Controls</maintainer>
+  <license>MIT</license>
+
+  <author email="sl-controls@saltybot.local">SaltyBot Controls Team</author>
+
+  <buildtool_depend>ament_cmake</buildtool_depend>
+  <buildtool_depend>ament_cmake_python</buildtool_depend>
+
+  <depend>rclpy</depend>
+  <depend>std_msgs</depend>
+  <depend>sensor_msgs</depend>
+
+  <test_depend>ament_copyright</test_depend>
+  <test_depend>ament_flake8</test_depend>
+  <test_depend>ament_pep257</test_depend>
+  <test_depend>pytest</test_depend>
+
+  <export>
+    <build_type>ament_python</build_type>
+  </export>
+</package>

jetson/ros2_ws/src/saltybot_battery_speed_limiter/saltybot_battery_speed_limiter/battery_speed_limiter_node.py

@@ -0,0 +1,152 @@
+#!/usr/bin/env python3
+"""Battery-aware speed limiter for SaltyBot.
+
+Subscribes to /saltybot/battery_state and publishes a speed limit factor
+on /saltybot/speed_limit_factor based on remaining battery percentage.
+
+Thresholds:
+  100-50%:  1.0 (full speed)
+  50-25%:   0.7 (70% speed)
+  25-15%:   0.4 (40% speed)
+  <15%:     0.0 (stop, preserve battery)
+"""
+
+import rclpy
+from rclpy.node import Node
+from std_msgs.msg import Float32
+from sensor_msgs.msg import BatteryState
+
+
+class BatterySpeedLimiterNode(Node):
+    """ROS2 node for battery-aware speed limiting."""
+
+    def __init__(self):
+        super().__init__('battery_speed_limiter')
+
+        # Parameters
+        self.declare_parameter('threshold_full_1', 100)       # 100%
+        self.declare_parameter('threshold_full_2', 50)        # 50%
+        self.declare_parameter('threshold_reduced_1', 50)     # 50%
+        self.declare_parameter('threshold_reduced_2', 25)     # 25%
+        self.declare_parameter('threshold_critical_1', 25)    # 25%
+        self.declare_parameter('threshold_critical_2', 15)    # 15%
+        self.declare_parameter('threshold_stop', 15)          # <15%
+
+        self.declare_parameter('speed_factor_full', 1.0)
+        self.declare_parameter('speed_factor_reduced', 0.7)
+        self.declare_parameter('speed_factor_critical', 0.4)
+        self.declare_parameter('speed_factor_stop', 0.0)
+
+        self.declare_parameter('publish_frequency', 10)
+        self.declare_parameter('enable_limiting', True)
+
+        # Read parameters
+        self.threshold_full_1 = self.get_parameter('threshold_full_1').value
+        self.threshold_full_2 = self.get_parameter('threshold_full_2').value
+        self.threshold_reduced_1 = self.get_parameter('threshold_reduced_1').value
+        self.threshold_reduced_2 = self.get_parameter('threshold_reduced_2').value
+        self.threshold_critical_1 = self.get_parameter('threshold_critical_1').value
+        self.threshold_critical_2 = self.get_parameter('threshold_critical_2').value
+        self.threshold_stop = self.get_parameter('threshold_stop').value
+
+        self.speed_factor_full = self.get_parameter('speed_factor_full').value
+        self.speed_factor_reduced = self.get_parameter('speed_factor_reduced').value
+        self.speed_factor_critical = self.get_parameter('speed_factor_critical').value
+        self.speed_factor_stop = self.get_parameter('speed_factor_stop').value
+
+        publish_frequency = self.get_parameter('publish_frequency').value
+        self.enable_limiting = self.get_parameter('enable_limiting').value
+
+        # Current battery percentage
+        self.current_battery_percent = 100.0
+
+        # Subscription to battery state
+        self.sub_battery = self.create_subscription(
+            BatteryState, '/saltybot/battery_state', self._on_battery_state, 10
+        )
+
+        # Publisher for speed limit factor
+        self.pub_speed_limit = self.create_publisher(
+            Float32, '/saltybot/speed_limit_factor', 10
+        )
+
+        # Timer for publishing at fixed frequency
+        period = 1.0 / publish_frequency
+        self.timer = self.create_timer(period, self._timer_callback)
+
+        self.get_logger().info(
+            f"Battery speed limiter initialized. "
+            f"Thresholds: Full={self.threshold_full_2}%, "
+            f"Reduced={self.threshold_reduced_2}%, "
+            f"Critical={self.threshold_critical_2}%, "
+            f"Stop={self.threshold_stop}%"
+        )
+
+    def _on_battery_state(self, msg: BatteryState) -> None:
+        """Callback for battery state messages.
+
+        Extract percentage from BatteryState message.
+        Handles both direct percentage field and calculated percentage.
+        """
+        # Try to get percentage from message
+        if msg.percentage >= 0:
+            self.current_battery_percent = msg.percentage * 100.0
+        else:
+            # Calculate from voltage if percentage not available
+            # Standard LiPo cells: 3V min, 4.2V max per cell
+            # Assume 2S (8.4V max) or 3S (12.6V max) pack
+            # This is a fallback - ideally percentage is provided
+            if msg.voltage > 0:
+                # Normalize to 0-1 based on typical LiPo range
+                min_voltage = 6.0  # 2S minimum
+                max_voltage = 8.4  # 2S maximum
+                normalized = (msg.voltage - min_voltage) / (max_voltage - min_voltage)
+                self.current_battery_percent = max(0.0, min(100.0, normalized * 100.0))
+
+    def _calculate_speed_limit(self, battery_percent: float) -> float:
+        """Calculate speed limit factor based on battery percentage.
+
+        Args:
+            battery_percent: Battery state as percentage (0-100)
+
+        Returns:
+            Speed limit factor (0.0-1.0)
+        """
+        if not self.enable_limiting:
+            return 1.0
+
+        # Apply thresholds
+        if battery_percent >= self.threshold_full_2:
+            # 100-50%: Full speed
+            return self.speed_factor_full
+        elif battery_percent >= self.threshold_reduced_2:
+            # 50-25%: Reduced speed (70%)
+            return self.speed_factor_reduced
+        elif battery_percent >= self.threshold_critical_2:
+            # 25-15%: Critical speed (40%)
+            return self.speed_factor_critical
+        else:
+            # <15%: Stop to preserve battery
+            return self.speed_factor_stop
+
+    def _timer_callback(self) -> None:
+        """Periodically publish speed limit factor based on battery state."""
+        speed_limit = self._calculate_speed_limit(self.current_battery_percent)
+        msg = Float32(data=speed_limit)
+        self.pub_speed_limit.publish(msg)
+
+
+def main(args=None):
+    rclpy.init(args=args)
+    node = BatterySpeedLimiterNode()
+    try:
+        rclpy.spin(node)
+    except KeyboardInterrupt:
+        pass
+    finally:
+        node.destroy_node()
+        rclpy.shutdown()
+
+
+if __name__ == '__main__':
+    main()

jetson/ros2_ws/src/saltybot_battery_speed_limiter/setup.cfg

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+[develop]
+script_dir=$base/lib/saltybot_battery_speed_limiter
+[egg_info]
+tag_build =
+tag_date = 0

jetson/ros2_ws/src/saltybot_battery_speed_limiter/setup.py

@@ -0,0 +1,34 @@
+from setuptools import setup, find_packages
+
+package_name = 'saltybot_battery_speed_limiter'
+
+setup(
+    name=package_name,
+    version='0.1.0',
+    packages=find_packages(exclude=['test']),
+    data_files=[
+        ('share/ament_index/resource_index/packages',
+            ['resource/saltybot_battery_speed_limiter']),
+        ('share/' + package_name, ['package.xml']),
+        ('share/' + package_name + '/config', ['config/battery_limiter_config.yaml']),
+        ('share/' + package_name + '/launch', ['launch/battery_speed_limiter.launch.py']),
+    ],
+    install_requires=['setuptools'],
+    zip_safe=True,
+    author='SaltyBot Controls',
+    author_email='sl-controls@saltybot.local',
+    maintainer='SaltyBot Controls',
+    maintainer_email='sl-controls@saltybot.local',
+    keywords=['ROS2', 'battery', 'speed', 'limiter'],
+    classifiers=[
+        'Intended Audience :: Developers',
+        'License :: OSI Approved :: MIT License',
+        'Programming Language :: Python :: 3',
+        'Topic :: Software Development',
+    ],
+    entry_points={
+        'console_scripts': [
+            'battery_speed_limiter_node=saltybot_battery_speed_limiter.battery_speed_limiter_node:main',
+        ],
+    },
+)

jetson/ros2_ws/src/saltybot_battery_speed_limiter/test/test_battery_speed_limiter.py

@@ -0,0 +1,319 @@
+"""Unit tests for battery speed limiter node."""
+
+import pytest
+from sensor_msgs.msg import BatteryState
+from std_msgs.msg import Float32
+
+import rclpy
+
+from saltybot_battery_speed_limiter.battery_speed_limiter_node import (
+    BatterySpeedLimiterNode,
+)
+
+
+@pytest.fixture
+def rclpy_fixture():
+    """Initialize and cleanup rclpy."""
+    rclpy.init()
+    yield
+    rclpy.shutdown()
+
+
+@pytest.fixture
+def node(rclpy_fixture):
+    """Create a battery speed limiter node instance."""
+    node = BatterySpeedLimiterNode()
+    yield node
+    node.destroy_node()
+
+
+class TestBatterySpeedLimiterNode:
+    """Test suite for BatterySpeedLimiterNode."""
+
+    def test_node_initialization(self, node):
+        """Test that node initializes with correct defaults."""
+        assert node.current_battery_percent == 100.0
+        assert node.enable_limiting is True
+        assert node.speed_factor_full == 1.0
+        assert node.speed_factor_reduced == 0.7
+        assert node.speed_factor_critical == 0.4
+        assert node.speed_factor_stop == 0.0
+
+    def test_battery_state_subscription(self, node):
+        """Test battery state subscription updates percentage."""
+        battery_msg = BatteryState()
+        battery_msg.percentage = 0.75  # 75% (0-1 range)
+
+        node._on_battery_state(battery_msg)
+
+        assert node.current_battery_percent == 75.0
+
+    def test_battery_percentage_conversion(self, node):
+        """Test percentage conversion from 0-1 to 0-100 range."""
+        battery_msg = BatteryState()
+        battery_msg.percentage = 0.5  # 50%
+
+        node._on_battery_state(battery_msg)
+
+        assert node.current_battery_percent == 50.0
+
+    def test_battery_zero_percent(self, node):
+        """Test zero battery percentage."""
+        battery_msg = BatteryState()
+        battery_msg.percentage = 0.0
+
+        node._on_battery_state(battery_msg)
+
+        assert node.current_battery_percent == 0.0
+
+    def test_battery_full_percent(self, node):
+        """Test full battery percentage."""
+        battery_msg = BatteryState()
+        battery_msg.percentage = 1.0
+
+        node._on_battery_state(battery_msg)
+
+        assert node.current_battery_percent == 100.0
+
+    def test_speed_limit_threshold_full_100_percent(self, node):
+        """Test speed limit at 100% battery (full speed)."""
+        speed_limit = node._calculate_speed_limit(100.0)
+        assert speed_limit == 1.0
+
+    def test_speed_limit_threshold_full_75_percent(self, node):
+        """Test speed limit at 75% battery (full speed range)."""
+        speed_limit = node._calculate_speed_limit(75.0)
+        assert speed_limit == 1.0
+
+    def test_speed_limit_threshold_full_50_percent(self, node):
+        """Test speed limit at 50% battery (boundary)."""
+        speed_limit = node._calculate_speed_limit(50.0)
+        assert speed_limit == 1.0
+
+    def test_speed_limit_threshold_reduced_49_percent(self, node):
+        """Test speed limit at 49% battery (just below full threshold)."""
+        speed_limit = node._calculate_speed_limit(49.0)
+        assert speed_limit == 0.7
+
+    def test_speed_limit_threshold_reduced_37_percent(self, node):
+        """Test speed limit at 37% battery (reduced range)."""
+        speed_limit = node._calculate_speed_limit(37.0)
+        assert speed_limit == 0.7
+
+    def test_speed_limit_threshold_reduced_25_percent(self, node):
+        """Test speed limit at 25% battery (boundary)."""
+        speed_limit = node._calculate_speed_limit(25.0)
+        assert speed_limit == 0.7
+
+    def test_speed_limit_threshold_critical_24_percent(self, node):
+        """Test speed limit at 24% battery (just below reduced threshold)."""
+        speed_limit = node._calculate_speed_limit(24.0)
+        assert speed_limit == 0.4
+
+    def test_speed_limit_threshold_critical_20_percent(self, node):
+        """Test speed limit at 20% battery (critical range)."""
+        speed_limit = node._calculate_speed_limit(20.0)
+        assert speed_limit == 0.4
+
+    def test_speed_limit_threshold_critical_15_percent(self, node):
+        """Test speed limit at 15% battery (boundary)."""
+        speed_limit = node._calculate_speed_limit(15.0)
+        assert speed_limit == 0.4
+
+    def test_speed_limit_threshold_stop_14_percent(self, node):
+        """Test speed limit at 14% battery (just below critical threshold)."""
+        speed_limit = node._calculate_speed_limit(14.0)
+        assert speed_limit == 0.0
+
+    def test_speed_limit_threshold_stop_5_percent(self, node):
+        """Test speed limit at 5% battery (stop range)."""
+        speed_limit = node._calculate_speed_limit(5.0)
+        assert speed_limit == 0.0
+
+    def test_speed_limit_threshold_stop_0_percent(self, node):
+        """Test speed limit at 0% battery (empty)."""
+        speed_limit = node._calculate_speed_limit(0.0)
+        assert speed_limit == 0.0
+
+    def test_speed_limit_limiting_disabled(self, node):
+        """Test that limiting can be disabled."""
+        node.enable_limiting = False
+
+        # Even at critical battery, should return full speed
+        speed_limit = node._calculate_speed_limit(10.0)
+        assert speed_limit == 1.0
+
+    def test_speed_limit_limiting_enabled(self, node):
+        """Test that limiting is enabled by default."""
+        node.enable_limiting = True
+
+        speed_limit = node._calculate_speed_limit(10.0)
+        assert speed_limit == 0.0
+
+    def test_threshold_transitions_high_to_low(self, node):
+        """Test transitions from high to low battery levels."""
+        # Start at 100%
+        assert node._calculate_speed_limit(100.0) == 1.0
+
+        # Transition to reduced at 49%
+        assert node._calculate_speed_limit(49.0) == 0.7
+
+        # Transition to critical at 24%
+        assert node._calculate_speed_limit(24.0) == 0.4
+
+        # Transition to stop at 14%
+        assert node._calculate_speed_limit(14.0) == 0.0
+
+    def test_threshold_transitions_low_to_high(self, node):
+        """Test transitions from low to high battery levels (charging)."""
+        # Start at 0%
+        assert node._calculate_speed_limit(0.0) == 0.0
+
+        # Transition to critical at 15%
+        assert node._calculate_speed_limit(15.0) == 0.4
+
+        # Transition to reduced at 25%
+        assert node._calculate_speed_limit(25.0) == 0.7
+
+        # Transition to full at 50%
+        assert node._calculate_speed_limit(50.0) == 1.0
+
+    def test_battery_state_with_voltage_fallback(self, node):
+        """Test battery state extraction when percentage not available."""
+        battery_msg = BatteryState()
+        battery_msg.percentage = -1.0  # Invalid percentage
+        battery_msg.voltage = 8.0  # 2S LiPo approximate mid-range
+
+        node._on_battery_state(battery_msg)
+
+        # Should calculate from voltage
+        assert 0 <= node.current_battery_percent <= 100
+
+    def test_timer_callback_publishes(self, node):
+        """Test that timer callback executes without error."""
+        node._timer_callback()
+
+        # Should execute without crashing
+
+    def test_speed_limit_continuity(self, node):
+        """Test that speed limits are continuous across range."""
+        for percent in range(0, 101, 5):
+            speed_limit = node._calculate_speed_limit(float(percent))
+            assert 0.0 <= speed_limit <= 1.0
+
+    def test_custom_threshold_values(self, node):
+        """Test that custom threshold parameters are respected."""
+        # Modify thresholds
+        node.threshold_full_2 = 60
+        node.threshold_reduced_2 = 30
+        node.threshold_critical_2 = 10
+
+        # Test new boundaries
+        assert node._calculate_speed_limit(60.0) == 1.0
+        assert node._calculate_speed_limit(59.0) == 0.7
+        assert node._calculate_speed_limit(30.0) == 0.7
+        assert node._calculate_speed_limit(29.0) == 0.4
+        assert node._calculate_speed_limit(10.0) == 0.4
+        assert node._calculate_speed_limit(9.0) == 0.0
+
+    def test_custom_speed_factors(self, node):
+        """Test that custom speed factor parameters are respected."""
+        # Modify speed factors
+        node.speed_factor_full = 1.0
+        node.speed_factor_reduced = 0.5
+        node.speed_factor_critical = 0.25
+        node.speed_factor_stop = 0.0
+
+        assert node._calculate_speed_limit(100.0) == 1.0
+        assert node._calculate_speed_limit(50.0) == 0.5
+        assert node._calculate_speed_limit(25.0) == 0.25
+        assert node._calculate_speed_limit(10.0) == 0.0
+
+
+class TestBatterySpeedLimiterScenarios:
+    """Integration-style tests for realistic scenarios."""
+
+    def test_scenario_normal_operation_high_battery(self, node):
+        """Scenario: Normal operation with high battery."""
+        battery_msg = BatteryState()
+        battery_msg.percentage = 0.85  # 85%
+
+        node._on_battery_state(battery_msg)
+        speed_limit = node._calculate_speed_limit(node.current_battery_percent)
+
+        assert speed_limit == 1.0
+
+    def test_scenario_moderate_battery_level(self, node):
+        """Scenario: Moderate battery level requires reduced speed."""
+        battery_msg = BatteryState()
+        battery_msg.percentage = 0.4  # 40%
+
+        node._on_battery_state(battery_msg)
+        speed_limit = node._calculate_speed_limit(node.current_battery_percent)
+
+        assert speed_limit == 0.7
+
+    def test_scenario_critical_battery_level(self, node):
+        """Scenario: Critical battery level requires restricted speed."""
+        battery_msg = BatteryState()
+        battery_msg.percentage = 0.2  # 20%
+
+        node._on_battery_state(battery_msg)
+        speed_limit = node._calculate_speed_limit(node.current_battery_percent)
+
+        assert speed_limit == 0.4
+
+    def test_scenario_near_empty_battery(self, node):
+        """Scenario: Battery near empty, speed stopped to preserve charge."""
+        battery_msg = BatteryState()
+        battery_msg.percentage = 0.08  # 8%
+
+        node._on_battery_state(battery_msg)
+        speed_limit = node._calculate_speed_limit(node.current_battery_percent)
+
+        assert speed_limit == 0.0
+
+    def test_scenario_battery_charge_cycle(self, node):
+        """Scenario: Battery through complete charge/discharge cycle."""
+        battery_percentages = [5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 90, 100]
+        expected_factors = [0.0, 0.0, 0.4, 0.4, 0.7, 0.7, 0.7, 1.0, 1.0, 1.0, 1.0, 1.0]
+
+        for percent, expected_factor in zip(battery_percentages, expected_factors):
+            speed_limit = node._calculate_speed_limit(float(percent))
+            assert speed_limit == expected_factor
+
+    def test_scenario_continuous_battery_update(self, node):
+        """Scenario: Continuous battery state updates."""
+        for percent in range(100, 0, -5):
+            battery_msg = BatteryState()
+            battery_msg.percentage = percent / 100.0
+
+            node._on_battery_state(battery_msg)
+            speed_limit = node._calculate_speed_limit(node.current_battery_percent)
+
+            # Should always return valid factor
+            assert 0.0 <= speed_limit <= 1.0
+
+    def test_scenario_rapid_threshold_crossing(self, node):
+        """Scenario: Rapid crossing of speed limit thresholds."""
+        thresholds = [100, 50, 49, 25, 24, 15, 14, 0]
+
+        for percent in thresholds:
+            speed_limit = node._calculate_speed_limit(float(percent))
+            assert 0.0 <= speed_limit <= 1.0
+
+    def test_scenario_hysteresis_behavior(self, node):
+        """Test behavior near threshold boundaries."""
+        # Test just below and above each threshold
+        test_cases = [
+            (50.1, 1.0),  # Just above 50% boundary (full speed)
+            (49.9, 0.7),  # Just below 50% boundary (reduced)
+            (25.1, 0.7),  # Just above 25% boundary (reduced)
+            (24.9, 0.4),  # Just below 25% boundary (critical)
+            (15.1, 0.4),  # Just above 15% boundary (critical)
+            (14.9, 0.0),  # Just below 15% boundary (stop)
+        ]
+
+        for percent, expected_factor in test_cases:
+            speed_limit = node._calculate_speed_limit(percent)
+            assert speed_limit == expected_factor