Copter loses altitude in Stabilze

ArduCopter Copter 3.4
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1

Hello,

I’m helping a client with a drone that is a bit on the heavy side, and is oddly shaped, but has flown before and was stable and predictable.

It’s worth mentioning that this drone PID values are real steep:
ATC_RAT_RLL_P 0.385
ATC_RAT_RLL_I 0.5
ATC_RAT_RLL_D 0.01
ATC_RAT_RLL_IMAX 2.1
ATC_RAT_RLL_FILT 20
ATC_RAT_PIT_P 0.755
ATC_RAT_PIT_I 0.64
ATC_RAT_PIT_D 0.013
ATC_RAT_PIT_IMAX 5.144
ATC_RAT_PIT_FILT 20
ATC_RAT_YAW_P 0.8000001
ATC_RAT_YAW_I 0.1
ATC_RAT_YAW_D 9.49949E-11
ATC_RAT_YAW_IMAX 0.221
ATC_RAT_YAW_FILT 5

Those are the values that were used with this drone in its last 10+ flights, and it flew real well.

Unfortunately, it had a bad crash and although nothing has been broken, it’s not flying properly anymore.
On stabilize it took off okay, roll and pitch are normal. But yaw causes it to drop in altitude.
On position hold - The same behaviour but after I stop yaw-ing the drone goes back to it’s original altitude.

On the last couple of flights it has worsen - On stabilize, for same throttle value the drone took off to about 6m, hovered for about 2 seconds, then dropped in altitude until reaching the (soft) ground. A log of one of these flights is attached. (Note: I believe it wasn’t ground effect, since the drone hovered for a bit, then dropped)
2017-03-21 13-29-28.bin (193.0 KB)

Does this sound familiar to someone?

Help with this issue is appriciated,

Thanks
NItay

2

Looks like motor one is at full power from the start of the flight. This means when you try to Yaw the copter it will loose altitude because it needs to lower the speed of two opposite motors to get it to Yaw.

Ether the copter is front right heavy or motor one is damaged.

It could also be that one of the motors is turned causing the copter to fight a yaw in the opposite direction since motor two is right behind motor one in power output.

Mike

3

Thanks for pointing me to this graph! It’s much more clear now.
While none of the motors look turned, it might be wind turning the drone around.

In any way this drone is at max weight capacity - And that’s what I will handle first. Thanks a lot for your help!!

Looking at the graph, there’s something I’d like to clear up:

Pasted image734×711 45.9 KB

Around the area where the red arrow is at, you see motos 3 & 4 lower while 1 & 2 are at max.
In theory, that probably means that the drone is resisting yaw by lowering power to the CW motors, causing the drone to fall as it is not generating enough lift. But it should have also added power to C2, and C2 isn’t rising at that point (at least not significantly)

Did i get this right? Is this the wanted behaviour?

Thanks
Nitay