I know my original post was long, but I have done a lot more reading. Specifically, I found this post. @xfacta I know you helped this guy a lot and I have a very similar build. Wondering if you have any advice. I think I am getting closer to the root cause of the solution based on many experiments.
I find that I can get the drone tuned pretty stiff and it feels good and responsive in the wind, but then with that tuning, I see problem with fast speed and slowing down. Specifically, there are a lot of oscillations on pitch axis when I slow down.
And I find that this only really happen when the throttle output drops below a certain value. So I have two competing theories and wondering what you think is the more probable (or maybe something else?):
- Since throttle is dropping so low during high speed braking, the notch frequency also drops low and increases the phase lag, resulting in oscillation and instability while it is in this mode of operation.
- It’s possible MOT_THST_EXPO not perfect and a little high. Maybe for this, motor outputs not scaling correctly at low range and causing instability.
I am using T-motor P80x, which have alpha ESC inside, but I previously do thrust stand experiment and think that it match about 0.82 the best. However, I can do some averaging on data and it look like maybe 0.7 also fit pretty good. I also see in the post linked above that he is using 0.7. Do you think a change from 0.82 to 0.7 could make a good improvement?
I also found a new filter setting that uses 72Hz frequency and has less lag:
Still need to test this though.
Thanks if you read this.