Hello all,
I've been flying an extended F450 (aerial mob arms) for quite a while. It's equipped with an E800 propulsion kit and two 6s 4Ah lipos. All-up weight is about 2800g, center of gravity is located dead-center of the frame ( at least on the xy plane ). Here is a picture of the machine by the time it was equipped with an E600 kit :

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The overall layout didn't change much, except that it uses now two lipos. I can post more recent pictures if that can help to cure the issue.


There isn't any drift or other abnormal behaviour except that it wobbles a bit when flying forward at full speed ( ~18 m/s GPS mode), the wobble gets worse if I try to gain altitude at the same time, or if I try to turn.
It seems to wobble most around a line that goes trough motor 1 and motor 3 - in other words motor 2 goes up and down if we look at onboard footage.

( motor numbers refer to this picture :    )

Here is what I tried to do :
-I tried to lower the center of gravity by having one lipo under the quad instead of having both lipos on top - it helped a bit.
-I also made sure the motors are perfectly paralell to the ground - helped a bit too.
-I tried to tell the assistant software the GPS puck position in a more precise way - not sure if that helped.
-I tried to use a lighter but more powerfull lipo ( higher C-rating  ) - didn't help.
-I configured a knob on my radio so that I could adjust gains during the flight. Therefore I tried to vary - while flying at full GPS forward speed - one by one all the basic gains from about  50% to 130%. It didn't have much effect on the wobble.  I ended up at 65% for pitch, roll and yaw and and 100% for vertical gain.

So thanks for reading me and if someone has an idea, let me know.
Bye

Try reducing the idle speed a bit and see if it helps alleviate the issue.

DJI-Jamie Posted at 2016-9-19 23:56
Try reducing the idle speed a bit and see if it helps alleviate the issue.

I tried to set the motors idle speed to minimum, did a 10 minute flight, doesn't seem to help.

xerocomus Posted at 2016-10-1 01:33
I tried to set the motors idle speed to minimum, did a 10 minute flight, doesn't seem to help.

Would it be possible to get a small video to see the extent of the wobble?

DJI-Jamie Posted at 2016-9-30 19:36
Would it be possible to get a small video to see the extent of the wobble?

Sure, here you go :

The wobble starts at 0:18.

xerocomus Posted at 2016-10-1 04:04
Sure, here you go : https://www.youtube.com/watch?v=smwfHQZKu8k&feature=youtu.be

The wobble start ...

And that happens only when you are using the elevator command and nothing else? What were your stick movements in the video prior to 0:18?

DJI-Jamie Posted at 2016-10-1 00:27
And that happens only when you are using the elevator command and nothing else? What were your sti ...

Prior to 0:18 my stick commands were full elevator and nothing else. But because it was loosing altitude a bit, I increased throttle  , and that is what initiated the wobble.

It doesn't wobble when I have full forward elevator and low throttle at the same time (negative vertical speed).

When I set the throttle in order to maintain the altitude ( vertical speed = 0 ) and have full forward elevator at the same time, then sometimes it wobbles, sometimes it doesn't. Usually an additional  yaw input or some wind initiates the wobble.

And if I have full forward elevator and try to gain altitude at the same time, then it always wobbles ( except if I decrease the elevator input).

xerocomus Posted at 2016-10-1 16:59
Prior to 0:18 my stick commands were full elevator and nothing else. But because it was loosing alt ...

The only thing that I can think of is that the arms may be too thin to handle the E800 motors when dealing with the extra resistance that vertical adjustments are generating, since you didn't mention having this issue with the E600s. A larger diameter may help alleviate the issue. The E800s are geared towards slightly bigger aircrafts.

DJI-Jamie Posted at 2016-10-5 22:17
The only thing that I can think of is that the arms may be too thin to handle the E800 motors when ...

I forgot to mention that the quad was wobbeling with the E600 kit too.

There is an other issue. The drone is loosing altitude at a rate of about 3m/s while flying atti mode at full forward speed. This altitude loss has been discussed hundreds of times on other forums, but I wasn't able to find any concrete solution. As mentionned above, I tried to fly with a light-weight high-discharge lipo : no improvement ( AUW = 2400g, Lipo 5Ah 60C )

If someone has an idea or a solution that might work...