feat: Add Issue #213 - PID auto-tuner (Astrom-Hagglund relay oscillation)
Implements PID auto-tuning ROS2 node using relay feedback (Astrom-Hagglund) method.
Service-triggered relay oscillation measures ultimate gain (Ku) and ultimate period
(Tu), then computes Ziegler-Nichols PD gains. Safety abort on >25deg tilt.
Features:
- Service /saltybot/autotune_pid (std_srvs/Trigger) starts tuning
- Relay oscillation method for accurate gain measurement
- Measures Ku (ultimate gain) and Tu (ultimate period)
- Computes Z-N PD gains: Kp=0.6*Ku, Kd=0.075*Ku*Tu
- Real-time safety abort >25° tilt angle
- JSON telemetry on /saltybot/autotune_info
- Relay commands on /saltybot/autotune_cmd_vel
Tuning Process:
1. Settle phase: zero command, allow oscillations to die
2. Relay oscillation: apply +/-relay_magnitude commands
3. Measure peaks: detect zero crossings, record extrema
4. Analysis: calculate Ku from peak amplitude, Tu from period
5. Gain computation: Ziegler-Nichols formulas
6. Publish results: Ku, Tu, Kp, Kd
Safety Features:
- IMU tilt monitoring (abort >25°)
- Max tuning duration timeout
- Configurable settle time and oscillation cycles
Published Topics:
- /saltybot/autotune_info (std_msgs/String) - JSON with Ku, Tu, Kp, Kd
- /saltybot/autotune_cmd_vel (geometry_msgs/Twist) - Relay control
Subscribed Topics:
- /imu/data (sensor_msgs/Imu) - IMU tilt safety check
- /saltybot/balance_feedback (std_msgs/Float32) - Balance feedback
Package: saltybot_pid_autotune
Entry point: pid_autotune_node
Service: /saltybot/autotune_pid
Tests: 20+ unit tests covering:
- IMU tilt extraction
- Relay oscillation analysis
- Ku/Tu measurement
- Ziegler-Nichols gain computation
- Peak detection and averaging
- Safety limits (tilt, timeout)
- State machine transitions
- JSON telemetry format
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
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