Re: GPS assist and Heli
« Reply #180 on: May 17, 2018, 07:08:35 am »
If you have an east / west oscillation that seems worse when pointed in some directions (when flying in PositionHold or VelocityRoam or probably GPSAssist'ed modes) you might look at this post and use the DJI.c that is attached there to compile your own firmware to match whatever version of next you are flying.


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Re: GPS assist and Heli
« Reply #181 on: May 17, 2018, 08:09:15 am »
Okay will look out for it and if have that issue, will test the dji.c fix


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Re: GPS assist and Heli
« Reply #182 on: May 20, 2018, 03:07:37 pm »
This weekend I had some experience and development
Flying some 30 min with the clone dji gps and concluded it was off some 11 to 29 degrees from direction of north, compared to my iPhone. Not always but randomly. Also showed toilet bowl OR slow oscillations in PositionHold (using AttEstAlgo= INS13+CF).
Decided to swop it for a genuine DJI unit (as much as anyone can check its genuine :)

The reason I did this is because I have another 450 heli with a dji unit and naza-h flight controller that can hover position hold rock steady. So at least the hardware will be okay.

After a 30 min wait and a really good GPS fix I redid the mag calibration. After that mag only off 0.1 - 0.3% and always green during the 30 min flights following. The dji mag and my iPhone agree all the time where north is located.

However, in Position hold it first hold position well but then increasingly start to move around on its own.
I can not determine if this is a toilet bowl behavior or the slow est/west oscillations.
I know this video do not give a clear view of whats going on but if anyone can spot the difference please check it.
Stab1 = rate mode, just lift off
Stab2 = attitude mode
then, Pos hold
then, VelocityRoam

B t w Altitudehold is rock steady and just a delight. Always something :)
« Last Edit: May 20, 2018, 03:21:50 pm by karla »

Re: GPS assist and Heli
« Reply #183 on: May 20, 2018, 06:08:07 pm »
An easy way to see how much the GPS drifts is to leave (not flying) in one place on the ground, bring up the Flight data page, then wait a half hour or so and look at the GPS map.  It will drift my several meters at times, and if in city with buildings (or other GPS reflective places) it may drift by much more.

At beginning of this, I recommend right click on GPS map, "Enable Diagnostics" so you can see the raw GPS data (added as diagnostics) as well as the cooked INS13 data.

I wonder if a simple recalibration with the clone GPS mag would have worked OK.
« Last Edit: May 21, 2018, 08:38:36 am by TheOtherCliff »

Re: GPS assist and Heli
« Reply #184 on: May 21, 2018, 08:48:38 am »
I have several of those same authentic DJI Naza GPS units.  They are small and work very well.

The only down side as compared to clones is that the authentic units have Ublox Neo6 GPSs inside, while the clones almost always have Ublox Neo8 or Neo7 GPSs.  That means the authentic ones only use USA satellites, and can't even see the Chinese Russia, etc, satellites.


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Re: GPS assist and Heli
« Reply #185 on: May 21, 2018, 01:54:33 pm »
Up until now I have identified the Mags to be my key problem and not the GPS.
Having a long hard march of toilet bowl I could not get rid of, and the analysis that its the mags telling the FC to go in a wrong direction and then compensation for the wrong in a wrong way will make it bowl eternally.
But now I think I have a reliable mag but maybe an unreliable GPS :(
However, the GPS is all green using 9 or more sats in an open field. I stays green until cuddly just go black for a second and then come green again.
What you think about trying your dji.c fix?

Re: GPS assist and Heli
« Reply #186 on: May 21, 2018, 07:58:39 pm »
Which GPS goes black, authentic or clone?  How often?  Using GCS or Android?

If GPS works at all, there should be only (GCS colors, I don't know about Android):
 - red X with black background (usually bad wiring or maybe bad GPS)
 - red block (GPS working but no satellites)
 - yellow block (GPS working, some satellites, but not enough)
 - green block (GPS working, enough satellites to fly)

Do you have FC powered by 5 volts or more or less?

dji.c fix only addresses the east-west oscillation issue which is worse when nose is pointing some compass headings.  For me I recall it was worst when nose was pointing north.  This is not toilet bowl.

Toilet bowl is usually caused by bad mag calibration or bad mag sensor mounting angle or aux mag orientation not set correct (example race mount motors).  Or aux mag Usage not set to AuxOnly.  Mag calibration is picky.  It gathers data the whole time, not just when you press button 6 times.  You cannot set it on ground or metal, etc. before/between/after button presses.  It takes two people to do it well and easily unless you have something like a waist high wooden table with no nails / bolts in say a 1x1m area to put quad on.

Magnets, like those in some Lipo alarms must be long way away from mag sensor.  My closest Lipo alarm is about 22cm from mag sensor, and I have watched GCS scopes and seen that is almost too close.  I can see mag graph change if I wave around a Lipo alarm any closer than that.


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Re: GPS assist and Heli
« Reply #187 on: May 22, 2018, 07:01:37 am »
Thank you!
. GPS used is the DJI authentic unit.
. Its a red X with black background.
. happens like 5 times during 11 minutes.
. Using GCS (win 10 pc and lp next r711)
. Power from LiPo 6s via Align BEC to flight controller at 5.0V (not more not less)
. It start slow oscillation east-west but then pick up north-south (it feels like toilet bowl but mags are super okay!).
. Only tried Pos hold with nose pointing North.
. Mag orientation should be fine, it does not differ more than 1-2 degrees from internal external mag.
. Mags are always green and show 0.1 to 0.3% error in GCS (best ever in years !).

I will do Mag calibration again several times for sure, (am aware of the common pitfalls).
However, something else might be wrong here...

This is what the Black out duration looks like:
However, it never happened during Position Hold flight, so if this is significant, then its telling something is wrong in general with this GPS?

« Last Edit: May 22, 2018, 07:13:14 am by karla »

Re: GPS assist and Heli
« Reply #188 on: May 22, 2018, 10:59:45 am »
All the authentic DJI GPSs that I have do not do that, only some brands of clones (most clones).

I recall that you are running next.  I worked on that code back in 16.09 version and red X was supposed to mean "bad data / no data received".  It is supposed to mean that you have some sort of hardware issue like cable disconnected or GPS sending bad data or GPS not sending any data.  I am guessing that next is the same as 16.09 in this regard.

My experience is that authentic DJI GPS does not send bad data, but some types of clones do.  Your report of how often it happens matches my observation of the clones that have bad firmware in them.  The good thing is that this is not noticeable in flight.

It actually garbles and drops about one GPS packet per second, so I have the system health ignore that.  (It looks like the person who wrote the GPS internal code increased the packet rate to compensate for that.   :P )  It drops two GPS packets in a row about once every minute or two and from what I recall, that is what you are seeing (red X).  It drops three packets in a row sometimes, maybe once an hour?  But that is still only 1/2 second without GPS data.  etc.

I have seen one of my clone GPSs lock up about every 24 hours of use.  I recommend that you do some long term testing to see what yours does.  Connect your aircraft to a 12 volt supply to bypass the battery and let it run for a week or whatever time you have if you don't have a week.  If the GPS is still running (no red X) (even red block is OK if the reason is that it is indoors) then I would not worry about it.  Beware that INS13 can diverge after sitting still for a long time (10 minutes or so?), causing ATTI/STAB health issues, but that isn't important for this test.

Beware that sometimes the FC will reset when you plug in USB with it already running on 12 volt power.  This shouldn't cause you problems (I don't expect the GPS to reset, so rebooted FC will still show if GPS is bad), but will reset the FlightTime counter (on Firmware page).  I like to see the FlightTime counter to make sure it has been powered the whole time (e.g. didn't reset last night from power failure, resetting the GPS).


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Re: GPS assist and Heli
« Reply #189 on: May 24, 2018, 02:24:48 am »
Thank you Cliff,
I got a quad running Librepilot next r711, were the gps is fully green at all times and now it do PositionHold very stable. I think I will move that unit over to the heli first to rule out if there is any issues with the frame. If that unit works well on the heli (its an OP v9) and can manage position hold I will know the dji naza unit is the culprit.