Can this Quad be tuned better?

Post AutoTune I have been trying manually to tweak this tune to get a more stable machine but now have run out of ideas and ask for some help.

It is a 9kg quad, T-Motor U8ii 190Kv motors, Alpha ESC, 2815 poly carbon props, custom frame, Orange Cube.

Post autotune it was quite twitchy and in Loiter almost unstable after a high-speed stop as it would overcorrect and do a final big correction.

The tuning steps I followed were.

  • Set the Throttle Based Harmonic Notch and Altitude Hold test
  • Autotune AUTOTUNE_AGGR 0.05. Got some ‘Can’t level, Manually tune’ messages but it completed all axes.
  • It was too sensitive so increased pitch and roll D from 0.001 to 0.01 which improved things.
  • Actual Pitch and Roll and Desired Pitch and Roll didn’t line up. Improved by increasing I so it is 2 x P??
  • Loiter – Instability and twitching when stopping.
    • This was improved by reducing PSC_POSXY_P from 1.0 to 0.3.
    • There was a small twitch at the end of the correction which was fixed by reducing LOIT_BRK_ACCEL from 100 to 50.
    • LOIT_BRK_DELAY set to 0.0.

The quad now flies quite well in Stabilized but there is still quite a bit of instability in Loiter which I would like to fix.

If anyone can suggest further improvements, it would be appreciated!