Loiter Braking Instability

ArduCopter
1

We’ve been working on tuning a quadcopter and are running into instability when the vehicle is braking in loiter mode.

When braking from high speeds the vehicle will rock back and forth several times before settling down, particularly when flying diagonally into the wind. Looking in the logs, the roll overshoots the desired roll (and pitch overshoots desired pitch) significantly (some flights upwards of 15 degrees).

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PosHold doesn’t exhibit this rocking behavior, but skids/slides a lot more than desired.

We’ve done an initial tune, added a harmonic notch filter and a couple autotunes and have been playing with these loiter/loiter brake parameters (I included what they were set to in the atttached bin file):
LOIT_ACC_MAX 450 cm/s/s
LOIT_ANG_MAX 25 deg
LOIT_BRK_ACCEL 250 cm/s/s
LOIT_BRK_DELAY 0.3 s
LOIT_BRK_JERK 50 cm/s/s/s

Unfortunately we haven’t found a combination that gives us good braking behavior. Any advice on which parameters you would tweak to fix this behavior? Does this look like a loiter parameter issue, a general tuning error or something else?

Here’s a link to the bin file and short video showing a few examples:
https://drive.google.com/file/d/10pUE46va7G8v7XazLJyyqrGFf-pcr8ZQ/view?usp=sharing

2

Your INS_HNTCH_REF,0.2974782 (the starting point for filtering) is higher than you hover thrust MOT_THST_HOVER,0.2554461 so harmonic notch filtering will not happen until thrust increases to 0.297 or more.

Set INS_HNTCH_REF to 0.2 and rerun Autotune

Try these Loiter params too
LOIT_ACC_MAX,600
LOIT_BRK_ACCEL,300
LOIT_BRK_DELAY,0.3
LOIT_BRK_JERK,300

3

Did you manage to solve this problem? I am facing the same situation with my drone :frowning:

4

Generally instability in Loiter is poor tuning elsewhere (attitude control).
So there’s no 1 simple fix, especially without a log file to check.
Also see if you can better describe what you see, and share a link to a .bin log file where this is happening.