Re: GPS modes oscillations
« Reply #30 on: November 01, 2018, 02:37:45 am »
Be aware that if Home Location is set say 50km away that GPS map position on GCS will be wrong by say several hundred meters.

For instance, if my Home Location is set to my friend's flying field that is 50km away and I am testing in my back yard, then the GCS map shows me several hundred meters away from my back yard.

RTB still works correctly and returns to where it took off from.  It thinks I took off several hundred meters away, and that is where it returns to; which happens to actually be in my back yard.


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Re: GPS modes oscillations
« Reply #31 on: November 01, 2018, 10:46:10 am »
Your description explains somewhat of my quad behaviour during several flight when home location was far away from takeoff. RTB and other GPS modes worked but with considerable horizontal drift (up to 10 meters) in various directions.

I plan to do some more flights at weekend with HomeLocation > Set set to False.

Re: GPS modes oscillations
« Reply #32 on: November 01, 2018, 11:20:36 am »
I haven't seen any drift or bad flight characteristics that I know for sure were caused by this.  Only that the GCS GPS map shows the wrong location.  On the other hand, I can't rule it out as I haven't researched it.  I also don't fly this way on purpose, so I don't do it often, and I can imagine some worse things if Home is a really long way away, like so far that the curvature of the earth is large.

The only bad things I imagine from 50km away from Home are that you are not flying where telemetry and the map says you are flying, and that if you use the GCS map to click up a waypoint flight then it is really bad because it does not fly where you think it should.

In my experience, most of my GPS drift has been caused by:
- not waiting long enough for GPS to fully "warm up"; up to 13 minutes for first flight of the day and much less for following flights
- GPS shadowing, like flying next to a tall building or in a canyon
- GPS signal reflections, like from a building or metal roof, or even cars

On first flight of the day, GPS downloads an almanac of satellite positions which can take up to 12 minutes after initial satellite signal.  Most GPS's (but not the cheapest, smallest GPS's) have the equivalent of a battery that lasts about 6 hours and powers the storage for the almanac.  Less than 6 hours between flights and it uses memory almanac, more than 6 hours and it has to download almanac again.

Once you get a good GPS lock, you can fly but if it finds an important satellite that it didn't see before, it will drift when it adds that satellite to it's list.  If it has the almanac, it knows where all the satellites are it is less likely to add an important satellite during flight since it already added it from the almanac.


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Re: GPS modes oscillations
« Reply #33 on: November 04, 2018, 10:01:38 pm »
with HomeLocation > Set set to False altitude on arming now is no more than 1-2m and VelocityRoam works fine.

Did you find out the cause of this?  I am going to guess that you have VtolPathFollowerSettings Max Horizontal Velocity (or similar name) set very high.  Maybe VtolPFS max bank angle set very high.  Etc.  ?

I haven't found out the cause but determined that this "strange" RTB is seen in case it is activated from Velocity Roam (probably from any GPS mode). And RTB works correct in case it is activated from Altitude Vario or Rate modes. Here is my today's footage. It contains 4 RTB passes.

Re: GPS modes oscillations
« Reply #34 on: November 05, 2018, 04:17:04 am »
Thanks for the clear documentation of the issue in the video.  I don't say it very often, but it looks like you found a bug.

Are you using RC failsafe or FC failsafe?

Do you use PID banks at all?  Or do all your flight modes use PID bank #1?

I don't test quad RTB by switching off my transmitter very much, I just make sure that RTB switch position works as it should and that it switches to failsafe when transmitter gets switched off.

Does anyone know if this has been found and fixed in "next"?  I don't see anything that looks like it by searching for failsafe or RTB.  I suspect that it is an issue with going into failsafe.
« Last Edit: November 05, 2018, 04:34:38 am by TheOtherCliff »


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Re: GPS modes oscillations
« Reply #35 on: November 05, 2018, 08:42:52 am »
I've got FS-IA6 radio with FS-iA6b receiver. As I understand my failsafe is RC.

But in my latest test I did not use failsafe. All I did was switch from AVar (Alt Vario) or VeRoam(Velocity Roam) to RTB. So I was able to easy get back from RTB. AUTO RTL on my OSD is not failsafe.

Alt Vario uses bank #3, Velocity Roam - bank #1, RTB - bank #1. And #1 and #3 almost the same.

By the way, in case of smooth/normal RTB behaviour calculation of RTB velocity gives me about 1 m/s while it should be 2 from Settings > FlightModeSettings.

Does transition to "Next" require sensor recalibration?
« Last Edit: November 05, 2018, 08:58:52 am by vgwit »

Re: GPS modes oscillations
« Reply #36 on: November 05, 2018, 08:05:13 pm »
There are ways to get to next without recalibration, but generally, next is a big change from 16.09, so it is recommended that you start over.

Uav files are human readable text files.  You can export settings from the old version, update and erase everything, export a default uav file in the new format, carefully find and hand copy all the calibrations from the old file into the new default file, and finally import the modified new file.  These calibrations are scattered into several different places inside these files.  Sometimes things get renamed.

So much depends on whether you have tweaked a lot or not, whether you plan to copy or redo your input/RC and output, ... PID banks, etc.  Basically look at each line in the file, understand what it is, and determine if you want to copy the value to the new file.  It doesn't matter whether the order is name then value or value then name.