APM 2.5 2.9.1 loses altitude in alt hold mode when yaw input applied.

Hello All,

I am currently tuning my new airframe and have got it flying pretty well in stab. I am now trying to get it flying currently in alt hold.

I get the airframe hovering nicely in stab mode and then select alt hold, the airframe seems to happily hold altitude until I start giving other inputs. Yaw seems to be the worst if I start to yaw the airframe it starts to loose altitude and doesn't really recover, I get similar results with pitch but maybe not as drastic as yaw input.

The airframe is a quad V with 120deg front arm separation and 80deg rear arm separation, 10" props on 850kv flying weight is around 1.7kg.

My question is which parameters do I need to look at to start correcting this behaviour?


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Any suggestions out there?

I am having the same issue.  Found this thread while searching for a solution.   Vibrations do not appear to be an issue in my case.

I am going to be equally unhelpful as Ken - I have exactly the same issue.  Mine will actually land eventually. 

I am having a same issue also. Did you solve this problem?

If you did. Let me know how did you do. pls.

Similar behavior sometimes happened to my quad (F450 + APM 2.6 +6M gps ) . I notice that when yawing in one direction until heading exactly north, the quad  suddenly lost its height  2-4 meters. If yawing in the  opposite  the quad will gain height 2-4 metered too.  This usually happened after the copter crash, So I fixed and performed a big alignment and  calibration ( balance the propellers, tightening the gps rod),  This behavior never appeared  again. So I believe that it should be from the vibration                        Somrit

I had same problem with apm 2.6 when sunny so changed the pink foam over the barometer for black transmitter case type foam which improved alt Hold alot

My very limited understanding is that asymmetrical quads (not + or X) just don't yaw very well. I'm sure someone can give you a more detailed description of the physics involved but the lack of symmetry just doesn't play well with fast yaw input. You can mitigate the effects best by adjusting the CG and optimizing the PID settings of the quad. I know of the effect through research and similar  troubles with my discovery. The biggest change for me was adjusting the CG to recommended point.

Please keep in mind that I am pretty new to flying so take my advice with a grain of salt. However I believe that what I outlined above should at least solve the problem partly.

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