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Old Aug 28, 2014, 03:07 PM
Registered User
United States, IN, Carmel
Joined Jan 2008
2,491 Posts
Question
Do I need to change the P or the I value?

My quad is a Locust MF450 with AX2810Q KV750 motors and meticulously balanced Gemfan 11x4.7 plastic props running on 3S voltage.

I have flown it with FY-41AP-M controller for quite some time and it was almost there with default settings.

Now FY-41AP found it's place in a fixed wing and the quad got a FY-DOS controller instead which is the same hardware sans OSD and airspeed sensor which is not needed in a multi anyways.
I did upgrade to the latest multicopter firmware too (2.3.1 beta) and the quad is rock solid in attitude mode. It flies very smoothly, and I have perfect manual control in every direction and climb/sink rate.

The problem is in GPS (or hovering) mode. When I activate it holds the position and altitude as it should and the quad is moving along very smoothly while I am holding the cyclic stick deflected, but when I am suddenly releasing it is starts oscillating back and front and side to side. The oscillations are of low amplitude (not more than 10 deg. in pitch and roll) and relatively high frequency. When it first happened I thought I am loosing it so I quickly switched to attitude mode and the oscillations immediately stopped. Then I did it again in higher-safer altitude and waited it out to see what happened. The oscillations continued and after approximately 10 seconds they gradually calmed down and the quad kept it's position in the sky.

I did it a lot of times and realized that the same phenomenon can also be triggered by a sudden gust of wind. It start oscillating while moving a few (1-3m) meters around then goes back to it's preset place. I could live with that and accept that this quad /flight controller combination does not cope wind gusts but what's more annoying is that I need to release the cyclic stick veeery slowly to avoid those oscillations. If I just let it go to center I have to watch it dancing in the air for quite some time.

I have no oscillations at all in the vertical (altitude) axis. The barometric sensor and respective settings work perfectly.

I also do not believe that's a GPS issue as I am using the latest blue uBlox 6M receiver, I have 3x green lights which means very good signal and the quad is literally locked in the sky when it finally settles down.
I am not talking about the infamous toilet bowl effect either - I had it before - I know what it is and it's not that. My magnetometer is calibrated in flight and I have no problems in yaw axis.

I believe that's a PID issue and the software lets me change the P value which is 60 now and the I value which is 10 (both default). What should I do?

Thank you in advance,
/Dimitris
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