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Hexacopter oscillates before takeoff (and makes bird noise)

PostPosted: Mon Dec 21, 2015 9:04 pm
by Astudillo
Hey Guy's,

I just replaced my esc's with the esc32V3 and did a calibration and the necessary thrust measurements to get quatos working.

If i want to take off the machines starts to oscillate quite a lot, but the moment it has lift, its kind of stops. And it flies oke.
If i land and throttle down the oscillation comes back again until a certain rpm and then the oscillation stops.

Here is a youtube video of the oscillation:


As you can see the Z axis goes berserk at takeoff and landing.
IMU.png

And the motor Graph looks real pretty, but not really healthy.
Motor.png


I played with A1 and A2 reducing it from -8 & -15 to -5 & -10 but that just made the machine sloppy.
I also reduced the L1_K1 to 5 and that reduced the oscillation a bit, but made the machine sloppy as well.

So what do you guys think? Should i even go for a lower L1_K1? Or is it something else?

Cheers,

Ray

Here is the Log file of the flight seen in the video.
003-AQL.LOG
(2.78 MiB) Downloaded 294 times

Re: Hexacopter oscillates before takeoff (and makes bird noi

PostPosted: Mon Dec 21, 2015 10:53 pm
by JussiH
If it only happens at low RPM on the ground, it may not be a big problem.

The oscillation in the arm is likely created by the prop resonating with the natural harmonic of the arm at a certain low RPM and load at a point when you are "almost" flying. This oscillation gets exited by the Quatos controller trying to cancel it out but not quite making it.

Once the motor is up to normal operation loads and RPMs, the prop frequency doe not resonate with the arm anymore and the values are normalizing. The log confirms it - the flying part is actually not too bad.

I wouldnt be too worried about it, if it only happens on the ground. It looks like the frequency where this happens is well below normal flight operation for your setup.

Re: Hexacopter oscillates before takeoff (and makes bird noi

PostPosted: Tue Dec 22, 2015 4:54 am
by LPR
Ray

I would try to increase the Quatos Max out from 4 to 8 and then play with the A1 and A2 settings again.

Larry

Re: Hexacopter oscillates before takeoff (and makes bird noi

PostPosted: Tue Dec 22, 2015 6:55 am
by aBUGSworstnightmare
Hi Ray,
if your TX permits you should configure it to have A1 and A2 on a proportional channel (pot, a digital trimmer is fine too).
This allows you to tune them in flight and gives you much better granularity compared to changing it by QGC.

Joerg

Re: Hexacopter oscillates before takeoff (and makes bird noi

PostPosted: Wed Jan 13, 2016 1:37 am
by Astudillo
Hey guy's

I connected AM1 and AM2 to the 2 pot meters on my radio. I reduced L1_K1 to 5 and upped the Quatos Max out to 8. Playing around with AM1 and AM2 i noticed by accident that when i upped the AM1 above -10 the oscillations at takeoff where drastically reduced. Im now at AM1-13.75 AM2-15.74 which is not even close to double that of AM1, but if i go any higher on AM2 starts to oscillates.
Could that be a problem that AM1 and AM2 are that close?

After tuning AM1 and AM2, i connected L1_K1 to the pot meter and tuned it to 11.
If i go higher the bird noise returns and some divergence on fast pitch or roll movements.

Here the results after the tuning:
Schermafbeelding 2016-01-11 om 10.16.49.png

Z axis seems a lot better then before.

And the motor graph looks a lot better as well.
Schermafbeelding 2016-01-11 om 10.06.42.png


I still have some trouble with keeping altitude on position hold(going up and down. But if i start moving the copter stays on altitude just fine. Could that be the noise on the Z axis? Or should i try to play with Nav altitude speed I ?

Cheers,

Ray

Re: Hexacopter oscillates before takeoff (and makes bird noi

PostPosted: Thu Jan 14, 2016 7:33 pm
by aBUGSworstnightmare
Would like to see your Quatos xml-File.
Some data on the craft itself (motors+props) would be nice as well.

Re: Hexacopter oscillates before takeoff (and makes bird noi

PostPosted: Fri Jan 15, 2016 12:22 am
by Astudillo
aBUGSworstnightmare wrote:Would like to see your Quatos xml-File.
Some data on the craft itself (motors+props) would be nice as well.

Here you go:
AQ6 Horus6V4.xml
(3.69 KiB) Downloaded 293 times


The motors are T-motor U3's and i use the 12" T-motor carbon props.
Here is the Thrust calc sheet:
thrustCalcU3-5S.xls
(24 KiB) Downloaded 283 times

The AUW is 4.3 kilo

Is there anything more you would like to know?

Cheers,
Ray

Re: Hexacopter oscillates before takeoff (and makes bird noi

PostPosted: Fri Jan 15, 2016 4:13 pm
by afernan
Explanation from Jussi it's very precise. Our controller is extremely sensible an quick so it will try to compensate any vibration, so it could amplify it. If the oscillations are during take off and landing its absolutely normal and acctable (it happens in real helicopters and aircrafts). Simply try to cross that frequency quick.

Anyway the best way to take care of all frequency matters withAQ is to have a frame as stiffer as possible. I'm just finished an exe similar to yours with very stiff arms that flies veeery smooth.
I attach my params for you to use as reference (I'm using ESC32v2)