[datapool]

thanks for giving me direction!

Yes, it was a bad PDB with "fluctuating" +5V - not stable. I installed a new PDB with clean 5.1v in any situation and now GPS and transmitter work fine without any breakdown. I also mounted the GPS on an antenna stand ~17cm. Now adjusting the flight characteristics - quite different with that mast above ;-) I am thinking of cutting the mast down a little to get better CG. But I will start with full atenna mount first.

Will calibrate and check GPS once I adjusted the PIDs for stable flight later today. But everyting mounted now to see if the magnometor on mast delivers more clean data to get a stable GPS position hold.

Before, I was comparing attitude hold with a clean stable auto height in complementary mode versus a GPS INS13 position hold. The auto height in attidue in complementary was more stable than the INS13 position hold. So hopefully with the antenna mount INS13 will get better for position hold.

Anyway... took some time to nail down the root cause for the bad PDB 5v distribution and reassemble everything. Will report back once GPS/mag calibration was done.

[TheOtherCliff]

Don't worry about being top heavy.  That shouldn't be a problem. 

Did you know that you must twist ALL your high current wiring so it has less effect on the mags?  Battery -> PDB -> ESC -> motor.  All of them.  If you suspect mag issues, this is the first thing you should check.  Also, I personally find that for normal FC locations, I must use an aux mag on quads smaller than 500mm.

The mast isn't going to help ALtitude stability in GPS flight modes.  GPS simply doesn't have good vertical accuracy, although a better GPS that tracks more sats can help.

You may consider building or downloading "next" which has AutoTune (see wiki).

[datapool]

Thanks Cliff and colleagues helping me out. GPS/mag looks like working now. VelocityRoam works. Need to finetune the stuff, but I am able now to get the GPS flight modes working. Will move on to finetune/recalibrate and start an autotune session.

THANKS!

Added:
I am so happy to have my first stable and controlled flights in GPS modes. Really fun getting this working!

Please allow one final questions:
It looks like there are some minor oscillations in GPS modes when I am in velocityroam on hovering - keeping sticks away. These oscillations are not there if hovering in non-gps modes. Are there different PIDs when using GPS flight modes? If so, can you give me a hint where to look and tune those?

[TheOtherCliff]

Yes there are PIDs in System -> Settings -> VtolPathFollowerSettings

But first question: "Is it Toilet Bowl?"  That is caused by bad high current wiring (twist all high current wire pairs / triplets).

[datapool]

All fine and stable now. Thanks for all hints. It would be impossible for me without this forum!

In INS13 mode now with no wind; I get I slow/light left-forward drift when hovering in attitude. So I should adjust the virtual aux mag rotation values to get a stable hover? Can you give me a short hint on which values to adjust if I see a very small left-forward drift?

Thanks!

[chromvis]

Were you hovering in Stabilize or in PositionHold? If in Stabilize, very slow drift is almost inevitable, although you can try to repeat board level calibration. If in PositionHold, unidirectional drift is a bit strange, but sometime GPS error could be up to 10 or even 20 m depending on the environment (tall buildings etc.). Horizontal position is mainly dependent on GPS, direction of position correction is dependent on magnetometer. If this direction is wrong the quad movement will look like water rotation while flushing toilet bowl - "Toilet Bowling". I got once swing-like movements, but there was a combination of wrong mag calibration and vibration.
In Stabilize mode some air flow reflected from some asymmetry in motor arms (ESC position, wires, LED etc) can create sufficient force to slowly move your quad in certain direction.

[datapool]

I am in stabilize. PositionHold is like a rock in the air.

So I think I will stop to "overoptimize"... I am quite happy so this little drift is only visible with no wind. No issue at all. Thanks for your comments. Helps me to learn and understand.

[TheOtherCliff]

Sorry for late reply.  I have been away for a while.

I do the following so that Attitude mode hovers as level and drift-free as possible, whether I use Basic or INS13.  Basic only uses accels for leveling, but INS13 uses accels plus mag for leveling, so first adjust accels with Basic, then adjust mags with INS13 so both are as good as they can be.

I use Attitude mode with Basic algorithm and adjust "rotate virtual" till I get a hover that moves very little / none (no wind, using down to 1/10ths of a degree); then I use Attitude mode with INS13 algorithm and adjust the mag rotations till I get a hover  moves very little (only degree whole numbers are allowed, so it won't be as perfect).