Re: [Paparazzi-devel] Copter isn't holding its position in hover (H_ZH) mode - with video!

[Sergey Krukowski]

Hi Simon!
I think the offset of 60° is not normal, even with wrong calibration.
Did you mount the board correctly? Try to check your board placing  
according this:

Thus in the northern hemisphere:
When you align your IMU with the direction of north, you should see x>0,  
y=0, z>0.
When pitching the IMU down, the magnetic vector is aligning with x, so x  
should increase and z should decrease to zero.
If yawing your IMU to the left, the magnetic vector is aligning with y, so  
y should be positive, x should decrease to zero and z stay positive.

And in the southern hemisphere:
When you align your IMU with the direction of north, you should see x>0,  
y=0, z<0
When pitching the IMU up, the magnetic vector is aligning with x, so x  
should increase and z should increase towards zero.
If yawing your IMU to the left, the magnetic vector is aligning with y, so  
y should be positive, x should decrease to zero and z stay negative.

But this is correct only in case of BODY_TO_IMU angles are close or equal  
zero.

Best regards,
Sergey

> Hi Ewoud, Felix,
>
> Yes, I took the previous current calibration completely out of the
> airframe file for the last test, to see the effect most clearly. It did
> drift a lot (around 80°!).
>
>
> The "real" direction in the screenshot above is around -60° the whole
> time. But as the copter keeps turning clockwise, I had to yaw left (the
> down steps of the green line).
>
> While replaying the flight, the GCS shows the copter pointing almost
> south while in reality it was still pointing roughly 300°. See the two
> walking paths marked in yellow and red and compare it with the video.
>
>
>
>
>
>
> As the next step I will do another current calibration and compare it
> with my earlier values. Though, my question is: Without any current
> calibration (like in the test above), do you get to see an psi offset of
> as much as 80-90°? This sounds a bit too much. Will a better current
> calibration help here or am I better off rewiring the power cables
> all-together?
>
> The full video: https://youtu.be/F1WrH9zZjNs
> In the video I am engaging hover mode three times. The last one @1:57 is
> quite dramatic.
>
>
> Simon
>
>
> Am 23.07.2015 um 18:33 schrieb Ewoud Smeur:
> > Hi Simon,
> >
> > Maybe your magnetometer picks up the magnetic field induced by the
> > current through the wires. You can calibrate for that:
> > http://wiki.paparazziuav.org/wiki/ImuCalibration
> > See the section 'Calibrating for current'
> >
> > Ewoud
> >
> > ------------------------------------------------------------------------
> > Date: Thu, 23 Jul 2015 15:54:22 +0200
> > From: address@hidden
> > To: address@hidden
> > Subject: Re: [Paparazzi-devel] Copter isn't holding its position in
> > hover (H_ZH) mode - with video!
> >
> > Hi Felix,
> >
> > I did another test earlier today. This time with more extensive
> > logging and again with video. The psi value seems to be off to the
> > left (ccw) during flight (not on the ground, though). But I am still
> > evaluating the data and comparing it with the video. Another post on
> > Youtube is to come once I am done synchronizing the screen cast of the
> > replay with the on-board recording from the GoPro.
> >
> > Sim
> >
> > Am 23.07.2015 um 15:09 schrieb Felix Ruess:
> >
> >     Hi Simon,
> >
> >     any updates here?
> >     Did you also test if the heading (psi value) stays the
> >     same/correct if you start rolling/pitching the quad?
> >
> >     Cheers, Felix
> >
> >     On Fri, Jul 17, 2015 at 9:41 PM, Simon Liebold
> >     <address@hidden <mailto:address@hidden>>  
> > wrote:
> >
> >         Hi Gautier,
> >
> >         A wrong heading estimate would explain it. But during a bench
> >         test right now the pointer on the GCS (and the value of int32
> >         psi) agree with the heading of my phone's magnetometer.
> >
> >         In the next few days I will test if the psi value changes when
> >         I ramp up the throttle. I did a current calibration. But maybe
> >         not correctly.
> >
> >         I will keep you posted.


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