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feat(controls): motor current protection (Issue #223) #224

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sl-jetson merged 1 commits from sl-controls/issue-223-motor-protection into main 2026-03-02 11:57:55 -05:00
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sl-controls commented 2026-03-02 11:54:26 -05:00
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sl-controls added 1 commit 2026-03-02 11:54:26 -05:00 
Monitors motor current, detects overcurrent (soft 5A, hard 8A), models thermal
state using I^2R heating model, and applies speed derating for safe operation.

Overcurrent Protection:
  - Soft limit: 5A (warning, trigger speed derating)
  - Hard limit: 8A (fault, immediate shutdown)
  - Monitors both left and right motor currents
  - Triggers emergency stop on hard fault

Thermal Derating (I^2R Model):
  Heat generation: P_loss = I^2 * R (both motors combined)
  Heat dissipation: P_cool = cooling_constant * ΔT
  Temperature dynamics: dT/dt = (P_loss - P_cool) / thermal_mass

  Temperature-based speed derating:
  - Full speed at ambient temperature
  - Linear derating from 25°C to 80°C limit
  - Aggressive derating near 80°C limit
  - Zero speed at or above 80°C

Combined Protection:
  - Speed derate = min(current_derate, thermal_derate)
  - Hard fault → 0% speed (immediate stop)
  - Soft fault → gradual derating based on current
  - High temperature → gradual derating approaching zero
  - Provides protective action before damage

Published Topics:
  - /saltybot/motor_protection (std_msgs/String) - JSON status
    * state (NORMAL/SOFT_FAULT/HARD_FAULT)
    * current_left, current_right, current_max (A)
    * motor_temp (°C)
    * soft/hard limits
  - /saltybot/speed_limit (std_msgs/Float32) - Thermal derate [0, 1]

Subscribed Topics:
  - /saltybot/motor_current_left (std_msgs/Float32) - Left motor (A)
  - /saltybot/motor_current_right (std_msgs/Float32) - Right motor (A)

Package: saltybot_motor_protection
Entry point: motor_protection_node
Frequency: 50Hz (20ms cycle)

Thermal Model Parameters:
  - Motor resistance: 1.5 Ω
  - Thermal mass: 100 J/°C
  - Ambient temperature: 25°C
  - Max safe temperature: 80°C
  - Cooling constant: 0.05 1/s

Features:
  ✓ Multi-motor current monitoring (worst-case approach)
  ✓ I^2R Joule heating with passive cooling
  ✓ Exponential temperature dynamics
  ✓ Two-level overcurrent protection
  ✓ Combined current+thermal derating
  ✓ Soft fault duration tracking
  ✓ Automatic recovery on current drop
  ✓ JSON telemetry with state and metrics

Tests: 25+ unit tests covering:
  - ThermalModel initialization and parameters
  - Current subscription and clamping
  - Overcurrent detection (soft, hard)
  - Fault recovery and state transitions
  - Joule heating calculation (I^2R)
  - Temperature rise and cooling
  - Speed derating (normal, soft fault, thermal, hard fault)
  - Derate clipping and bounds
  - JSON status format
  - Realistic scenarios (thermal rise, overcurrent spike, asymmetric loading)
  - Combined current+thermal derating

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
sl-webui force-pushed sl-controls/issue-223-motor-protection from c00688cd7e to 4730ea46d1 2026-03-02 11:57:22 -05:00 Compare
sl-jetson merged commit 3a7cd3649a into main 2026-03-02 11:57:55 -05:00
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Reference: seb/saltylab-firmware#224
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