cato

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A-GPS for the V9
« on: July 22, 2015, 10:51:29 pm »
Hi guys,

I wonder if there is a way to make it possible to load A-GPS data to the GPS Platinum? I got the idea when I found on my mobile a menu which does exactly that. Also the software there shows, when A-GPS data have last been uploaded to the GPS.

I could imagine that the A-GPS Data download and GPS upload could be done through the GCS?

What do the devs think of that idea?
Nighthawk 250, MT1806, 12A ESC OneShot125, Revo, M8n GPS, FPV
Cinetank MKII, Elite 2216, 30A Afro OneShot125, Revo Clone, M8N GPS

f5soh

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    • LibrePilot
Re: A-GPS for the V9
« Reply #1 on: July 23, 2015, 08:49:33 am »
Hi,
It was discussed some time ago, if i remember not only agps data from ublox server but also for data storage in GPS flash or MCU.

cato

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Re: A-GPS for the V9
« Reply #2 on: July 24, 2015, 09:50:58 pm »
sounds good,

I have a special reason for that. Somehow my gps seems to have lost all data. It needed several weeks to come back, and now with 15.05., when I had to erase the revo, it seems it lost it's data again. Right now sometimes it has fix within seconds on hot start, sometimes it needs hours (up to 7 hours!)

As this is slowly improving again, I think it's not a technical defect but caused by a software problem (which may very well have triggered myself by experiments).
Nighthawk 250, MT1806, 12A ESC OneShot125, Revo, M8n GPS, FPV
Cinetank MKII, Elite 2216, 30A Afro OneShot125, Revo Clone, M8N GPS

Re: A-GPS for the V9
« Reply #3 on: August 10, 2015, 08:41:52 pm »
From my limited research, A-GPS needs an internet connection and only helps during the first startup of the day.  It might even be possible to download the data at home, and have the GCS send it to the GPS at home or at the field.

If you have 15 minutes in your schedule to run GPS normally, for GPS to download almanac, it doesn't seem helpful.  If you have an internet connection where you fly, and have a GCS running, it would save you 15 minutes on your first flight (once the code is written).  What I do is that the first thing I do when I get to the flying site is power up my quad while unpacking other stuff.

Sorry for the late post.  I haven't been on Forum as much as I should.

I can tell you a few things that I have experienced.

I have a Nano with a GPSV9 that works fine.  That quad also has an OPLink set to 50mw for telemetry.  All this works fine with all the LP builds I have used on it (at least 3).

Some things I can point to that would cause problems:
- A transmitter nearby (on the aircraft); that could be FC telemetry, RC Rx, FPV Tx, etc.
- Anything large (like a house or canyon wall) or conductive (like a battery or a carbon fiber plate) above the GPS module and blocking (at least some large part of) the sky; this includes beside or between buildings
- GPS hardware problems
- Not waiting at least 15 minutes (with quad powered up and sitting out in the open) before first flight of the day
- Very dense cloud cover
- GPS not mounted right side up :)

You should test with FPV transmitter off and again with it on to see if it causes a problem.  Even better, you could use telemetry to tell you how well GPS is working.  Set quad outside with FPV Tx off, and let it acquire satellites for at least 15 minutes.  It should not take longer than 15 minutes because once it sees any satellite, it can download the whole satellite almanac in 12 minutes.  Look at (and maybe screen capture) GCS -> System -> Data Objects -> GPSPositionSensor (PDOP and Satellites especially) to see how well the GPS is working.  You can also look in GPSSatellites (SatsInView and SNR (Signal to Noise Ratio, higher is better)).  After capturing data with FPV Tx off, switch it on, wait 3 minutes or more, capture GPS performance data that way.  Compare the two sets of data.

I can say that the V9 that I have does not acquire satellites indoors as well as my cheap eBay Neo6 GPS does.  But it does work well and it flies well.

There is a small rechargeable battery on most GPS units.  That battery size typically lasts less than a week, but the almanac can change more frequently than that.  The GPSV9 has a supercap instead of a battery, these don't wear out like batteries, but it only lasts 5 or 6 hour, so the V9GPS looses its settings (if not recharged by powering it up for a few seconds) and must be go through the 15 minute almanac download after being unpowered for 5 hours.

The general rule you must follow is that before the first flight of the day, you must set the vehicle out in the open, powered up for at least 15 minutes.  Do this every day you fly it.  GPSV9 supercap only lasts 5-6 hours, so you need to redo the 15 minute download if the GPSV9 has been unpowered for 5 hours or more.

If sitting out in the open, powered up, for 15 minutes does not give you a good satellite fix, you should take the GPS out of the quad, and run the same test with it only connected to a laptop running u-center.exe.  That will tell you whether you have a bad GPS or whether something about your aircraft is causing the problem.

Wagsy

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    • Rotorpix
Re: A-GPS for the V9
« Reply #4 on: September 11, 2015, 09:58:35 am »
Great to know, I was wondering why sometimes it would not arm after going to a new location.
Guess I will just have to wait longer.