No GPS, start in manual then switch to loiter?

Hi all.  So I'll be filming a lot in the mountains, canyons, where GPS signal is weak until you get up higher out of the canyons.

I'm curious how it would work if I start off in manual mode without GPS signal, then I get high enough to get signal and switch to the LTR mode.  Would this work?  Can I switch mid flight and lock on to GPS?  Or does it need to be perfectly still to lock on?

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  • Hey Justin I'm Alaska based and have experienced this same issue.
    What Erik is proposing w/ Alt Hold will work, but keep in mind that the elevation
    accuracy can get skewed based on temperature changes in the air. This may add confusion
    to any conclusions about when GPS 3D lock actually kicks in if it's intermittent through out the flight.
    You can set your preferences in Tower GCS to read HDOP and announce it every 30 sec.

    Alt Hold is a great fall back if GPS issues come up, only down side is your bird will be subject
    winds so be ready with the sticks as you climb out of the protection on valleys. Alt hold is only good
    for vertical axis hold. Also keep in mind that Stabilize is the only truly responsive & crisp flying mode.
    This is important at higher elevations bc air gets thinner as u go up so thrust & throttle won't be the same as ASL.
    It's also worth mentioning your battery is gonna loose it's spunk later into the flight so do the risky stuff earlier.

    I like to fly my Iris (non+) w/ payload & 10X5.5 props. It's a good idea to practice a few times taking control of the bird from a far distance in Stabilize just in case GPS goes poo poo. The method I was taught for this was to pitch forward and watch to see which direction the bird goes. This is going to feel counter intuitive bc you want to bring the bird back but stick with it and you will get a sense of direction. From there you'll know how to correct to steer it back. Plan ahead so you know relative distances to rock faces/peaks based on your anticipated flight path.

    Also, if you can, it's worth setting up your TX with Loiter to Althold/stabilize w/ one flick of a switch. This
    will shorten your reaction time & simplify steps in case the the bird goes haywire. The goal to minimize having to
    look away or down in these situations. 

    Personally, I wouldn't recommend tweaking HDOP parameters till your comfortable recovering at a distance. That would be like swimming long distance in open water w/o knowing a basic recovery position for rest & recovery.

    The site below is handy for planning around ideal HDOP for flights

  • You could also go into the parameters and raise the HDOP required value. I had a similar situation and raised it to 3 with no problem. 

    • High GPS HDOP : the GPS’s HDOP value (a measure of the position accuracy) is above 2.0 and the vehicle is in a flight mode that requires GPS and/or the circular fence is enabled.  This may be resolved by simply waiting a few minutes, moving to a location with a better view of the sky or checking sources of GPS interference (i.e. FPV equipment) are moved further from the GPS.  Alternatively the check can be relaxed by increasing the GPS_HDOP_GOOD parameter to 2.2 or 2.5.  Worst case the pilot may disable the fence and take-off in a mode that does not require the GPS (i.e. Stabilize, AltHold) and switch into Loiter after arming but this is not recommended.

  • That will work.  Start in Alt Hold.  Watch your GPS reception as you go up.  Switch to Loiter, but keep an eye on the Iris.  If it starts going haywire, be ready to switch right back to alt-hold.  Don't forget to switch back to Alt Hold on the way to land.

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