Overview

The AUTOTUNE parameter group configures the AutoTune flight mode. This is an automated system-identification routine where the autopilot rapidly twitches the vehicle in Roll, Pitch, and Yaw to measure its physical response (inertia, authority, damping) and automatically calculates the optimal PID gains (ATC_ group).

Key Concepts

1. Aggressiveness (AUTOTUNE_AGGR)

This parameter controls how "sharp" or "locked-in" the resulting tune will be.

• 0.1 (Default): Standard crisp tune. Good for most racers and camera drones.
• 0.075: Softer tune. Better for large cinematic builds, older frames, or if the default tune causes oscillation.
• 0.05: Very soft/damped.

2. Axes Selection (AUTOTUNE_AXES)

Selects which axes to tune during the session.

• 1: Roll only.
• 2: Pitch only.
• 4: Yaw only.
• 7 (Default): Roll, Pitch, and Yaw.

Parameter Breakdown

• AUTOTUNE_AGGR: Aggressiveness target.
• AUTOTUNE_AXES: Bitmask of axes to tune.
• AUTOTUNE_MIN_D: Minimum D-gain to ensure damping.

Integration Guide

Running AutoTune

1. Setup: Map a switch to AutoTune mode (or use AUTOTUNE_AXES).
2. Safety: Find a large open area on a calm day.
3. Process:
   • Take off and establish a stable hover (AltHold or Loiter).
   • Switch to AutoTune.
   • The vehicle will start twitching (Roll -> Pitch -> Yaw).
   • Pilot Input: If the vehicle drifts too far, use the sticks to gently bring it back. The tuning pauses while sticks are moved and resumes when centered.
4. Completion: The twitching stops. Land and Disarm to save the new PIDs. Switch out of AutoTune before disarming to discard them.

Developer Notes

• Library: ArduCopter/mode_autotune.cpp
• Algorithm: Iterative Step Response optimization. It tries to match the requested Rate vs Actual Rate with minimal overshoot.