No GPS lock with 8 Sats

Discussion in 'ALTA 8' started by Andrew Pollock, Aug 9, 2016.

  1. Andrew Pollock

    Andrew Pollock New Member

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    Hey guys having a bit of a head scratcher here. Flying an Alta 8 on the latest firmware. I'm not getting a GPS lock even with 8 satellites. Was doing some test flights for a shoot tomorrow and I noticed the issue. If i tried flicking into GPS mode the copter would drift as if it was in Hight hold. For a short time during one flight the GPS started working and it would hold position but within a minute or two it stopped working again. The main reason I'm worried is because I might have to fly some big wide shots tomorrow and I'm concerned return to home won't work on the odd chance I lose signal.

    Anyone got ideas?

    Thanks,
    Andrew
     
  2. Steve Maller

    Steve Maller UAV Grief Counselor

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    I assume you've done a compass calibration? And how long did you wait for a lock? If you've recently moved to a different location than the last time you had a good lock, it can take quite a while to reacquire the satellites and rebuild the internal database. I've had that take as long as 5 minutes.
     
  3. Andrew Pollock

    Andrew Pollock New Member

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    I updated the firmware two days ago and after the update i calibrated the compass. From what i remember GPS was working alright then. Flying (in the same location) today I did about 5 flights, total flight time around 20minutes and i rebooted the copter 2-3 times during that time. The copter was probably powered up for around 40min. I was in open field with nothing to block satellites. By the way I'm in South Africa.

    UPDATE:

    I reverted to the previous firmware, still had the problem so I updated again to the latest version. Went out back to the field this time without camera. I was flying a M15/RED top mounted on the previous flights. I redid the compass calibration. I was now getting 10 sats and after a minute or two i got a GPS lock. Here is the weird thing, If i flew slightly aggressively, I would lose the GPS lock and Fix, it would take about 10-15 seconds to come back once i slowed the copter down. I didn't even have to fly that aggressive, If i put it in GPS mode and gave full forward stick it would move forward and then within 1 or 2 seconds lose lock and go back to height mode and accelerate aggressively.

    At least the RTH is working now (i tested it) but the GPS issue is a bit concerning even though I very rarely fly in GPS mode.
     
    #3 Andrew Pollock, Aug 9, 2016
    Last edited: Aug 9, 2016
  4. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Andrew:
    Is there anything obscuring the sky view of the GPS antenna? Any wiring very close to the antenna? Could you post an image of your setup showing the GPS antenna in relationship with the M15/Red?

    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  5. Andrew Pollock

    Andrew Pollock New Member

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    Hi Andy

    The problem is not only in sky view and the copter is pretty much standard we were shooting with the camera underneath today and the problem was persisting. We were shooting in a bit of a valley so we had 7-8 sats but never got a lock and fix for more than a few seconds. It was a bit concerning not having RTH as we had to fly quite far away and I also had no distance, height or speed telemetry.

    The machine just came back from freefly in the last two weeks for the motor mount issue. Its flown one other job since its been back and the GPS was working fine then. Any ideas on how to troubleshoot this?
     
  6. Gary Haynes

    Gary Haynes Administrator
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    Andrew depending on where you are flying, the actual elevation of the satellites in view and the impact of a high K index over the last several days/weeks all can have an effect on the usability of GPS signals. K index has been running up and down near a 4 value which is degraded with several days over that. Low elevation line of sight will also have an impact. Seeing the sats doesn't mean that you will get a lock. Lastly might be an antenna, connection issue.
     
  7. Andrew Pollock

    Andrew Pollock New Member

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    Thanks Gary

    I'm heading home tomorrow and ill give the copter a test flight once back and see if anything has changed. If it hasn't any idea on how to check the antenna is connected correctly?
     
  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    You could certainly just undo the GPS antenna a couple of turns and then snug it back down to make sure it's making good contact.

    If you could move a recent log file from the microSD card over on to a PC/Mac you can open up the .csv file using Excel and then look in columns EJ to EL to see the accuracy you're getting (Hacc typically around 0.52 and Sacc around 2.1 for the one I looked at).

    But, as Gary says, the KpIndex has been at 4 (check n3kl.org or uavforecast.com) and that could explain some of the problems.

    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  9. Andrew Pollock

    Andrew Pollock New Member

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    Hi Andy

    I really dont think, the KP Index is the issue, I saw someone flying a phantom nearby and he had no issues and was clearly flying in GPS. None of our other GPS gear had any issues either.

    I took the copter out for another test flight today with one of the pilots i work with. The company we fly for has 4 Altas and none of them are doing this. The GPS managed to get between 7-8 sats and during the hour or so we were flying it got a GPS fix and lock for maybe a minute. As soon as I flew with a bit of speed it lost it again. I checked the GPS antenna it it was secure.

    One other thing we noticed was that the copter was losing its level sometimes. To be fair we were flying fairly aggressively as we had no camera attached but it was drifting pretty badly. Sometimes we landed the copter took off 30 seconds later and it was still not levelling correctly. None of the motors had excess vibration.

    The other pilot has a lot of flight time on the Altas and he hasn't had these kinds of problems before.

    Unfortunately I dont have the machine with me at the moment so i can't check the flight data.

    At this point should i get in touch with freefly directly?
     
  10. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Andrew:
    All good data -- I think you're right. There is some other issue with the aircraft and opening a support ticket by emailing to support@freeflysystems.com is the most cost-effective thing to do with your time -- trying to trouble shoot this kind of behavior is going to drive you bonkers.

    Andy.

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  11. Steve Maller

    Steve Maller UAV Grief Counselor

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    I had numerous GPS gremlins with an older copter that bedeviled me just like this. I finally tracked the problem down to a voltage converter I had installed to power my FPV camera (I think). It was very noisy and was interfering with the GPS radio frequencies. Once I removed it and replaced it with a properly-shielded and filtered supply, the GPS problems disappeared.

    The problem could also be an video transmitter. Are you, by any chance, using a 1.3gHz FPV transmitter? They're notorious for emitting harmonics in the 2.4gHz range that's used by GPS.

    I might try removing everything from the copter (MōVI, FPV, etc.) and testing it. The problem could also be a defective component in the ALTA/SYNAPSE itself. But you should eliminate all the aftermarket stuff first before you send it back to Freefly.

    I also found that a radio frequency analyzer was helpful, but that was more for when I was doing more custom builds. I don't use it much anymore. :)
     
  12. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    That's a good idea, Steve. If there is a "noise generator" on the aircraft it could easily swamp the GPS signal.

    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  13. Andrew Pollock

    Andrew Pollock New Member

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    Thanks for the idea. The only thing on there is a 5.8 transmitter, from what i understand its the one that came with the machine. I have emailed freely support, I'm sending them some flight logs, hopefully they can figure it out.

    If anything of interest comes of it ill post here.

    Andrew
     
  14. Steve Maller

    Steve Maller UAV Grief Counselor

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    Where do you live? You might want to check around locally if there's an RC nerd (like me) who might have one of those frequency analyzers I mentioned who'd be willing to spend a few minutes with you and look at the RF environment around your ALTA for clues. If there's an AMA chapter they could probably be of assistance (assuming you're in the US). It should be relatively easy to sample the GPS RF bands for any noise emanating from your ship. Have you tried flying it without the MōVI on board using just the battery tray/landing gear? Could it be something on the MōVI? Some cameras are extremely noisy and could cause problems.
     
  15. Andrew Pollock

    Andrew Pollock New Member

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    Hey Steve

    Thanks for all the ideas, I'm actually in South Africa, which isn't ideal if this thing needs to be shipped back to the states, it actually just came back 3 weeks ago for the motor mount issue. We have flown it with no payload, the problem is still the same. I also think it should be able to work with the standard gear we use (connex, Teradek) as thats whats its made for, flying cameras. I'm going to send some flight data to freefly on Monday and we will see what they have to say. The company i work for has a total of 4 Altas and the senior pilot test flew the copter with me yesterday and agreed something was wrong with this particular machine.

    Hopefully it can be sorted without it going back to the states.


    I'll update here once i hear back from Freefly.

    Andrew
     
    #15 Andrew Pollock, Aug 13, 2016
    Last edited: Aug 14, 2016
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  16. Andrew Pollock

    Andrew Pollock New Member

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    Hey guys, we found the problem. It was the GPS antenna, it had come loose at the solder points. I think it was slightly loose and became worse over time. I was in touch with the guys at freefly and they were happy for me to resolder it which i did. Did a test flight this morning and its working perfectly.

    Im not sure how it happened, we are pretty careful with the gear but when moving a fully loaded machine around a knock to the antenna could do that.


    [​IMG] [​IMG]
     
    #16 Andrew Pollock, Aug 16, 2016
    Last edited: Aug 17, 2016
    Humberto Barchini likes this.
  17. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Good find, Andrew.
    Glad you managed to resolve it -- and thanks for posting the images in case anyone else has the same issues.

    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     

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