AutoTune gave up: it could not find a gain

What ArduPilot says:

• AutoTune: Angle P Gain Determination Failed
• AutoTune: Failed
• AutoTune: Rate D Gain Determination Failed
• AutoTune: Rate P Gain Determination Failed
• AutoTune: Twitch Size Determination Failed

AutoTune pushed a gain to the edge of what it allows without getting the response it looks for, and stopped; you are flying on the gains from before. “Twitch Size”: the aircraft kept reaching the angle limit before its rotation rate peaked, however small the twitch was made. “Rate D”: the bounce back after a twitch stayed too large with D already down at AUTOTUNE_MIN_D. “Rate P”: P had to be cut to its floor of 0.01. “Angle P”: the angle still overshot with angle P at its floor of 0.5. “AutoTune: Failed” on its own is the traditional helicopter's wording.

What to do, most likely first

1. Vibration and noise reach the gyro, so the measurements jump from one twitch to the next.

   CheckThe log's vibration levels, and whether the harmonic notch filter is set up (the Setup & Tuning Guide's filter steps).

   FixBalance the props, fasten what is loose, set up the notch filter, then try again.

2. The frame or its arms flex, or the flight controller rocks on a soft mount.

   FixStiffen the frame and the mounting; AutoTune cannot tune out a structure that moves.

3. The motors do not answer evenly: MOT_THST_EXPO does not suit the props, or MOT_SPIN_MIN is so low that a motor nearly stops on the slow side of a twitch.

   FixSet MOT_THST_EXPO and MOT_SPIN_MIN as the Setup & Tuning Guide's motor steps describe, then tune again.

4. “Twitch Size”: the aircraft turns too slowly for the test: heavy, short of power, or starting from very low gains.

   FixTune roll and pitch by hand to a firm hover first, and keep the lean angle limit at its default of 30° or more.

5. “Rate D”: AUTOTUNE_MIN_D is above what a large aircraft with slow props needs.

   FixLower AUTOTUNE_MIN_D (0.0005 by default, down to 0.0001) and run the tune again.

Parameters to look at

Where to do it:Setup & Tuning GuideSetup & Tuning GuideSetup & Tuning GuideSetup & Tuning Guide