Hi, I've made the same post on apm, however no one thought it was interesting enough to read, but I badly need some answers from knowledgeable people so doubling it here:
Last Sunday crash-finished my 50+ flight with the current setup. Unfortunately didn't have telemetry as it was a quick FPV fun flight w/o gimbal/gopro so no tlogs. Only APM logs wich I'll be attaching.
Here is the relevant info:
Tricopter 120*, 380kv/4s apm 2.6 w/ external GPS MAG 3DR combo.
running AC3.1.3. (after autotune completed was rock stable, loiter was excellent)
1.2ghz lawmate vTx at 1080mhz channel with a lowpass filter (proven no issues with frsky x8r at 1km)
was flying nearby for 14+ min, flipped RTL just to test -> works awesome, copter comes home, I take over the control and continue in alt hold, switch to loiter, decide to test it again, copter shoots full throttle in the opposite direction it was supposed to go, flipping back to alt hold-> no reaction, continues full throttle "south", flipping to stab, throttle down starts falling, trying to recover unsuccessfully. resulting in 2 broken props (only)
logs show: GPS Err2 right after RTL engaged. (now I know why it shoot "south") but what I do not understand is Err Fligh Mode-5 message right after GPS Err-2, why would a copter fail to enter a flight mode?
also, if anyone has an idea why GPS can throw an error with 11 satellites and HDop1.6 at the time of error rapidly going to 9sats and HDop 1.8 ? could it indicate a bad GPS? (usually I have 11 sats in the first 60 seconds at that very same spot, this time it was only 6 and than 9 later in flight and than 11sats after 10+min)
Replies
GPS glitch will be invoked if the change in location doesn't match what predicted path is. Check out
http://copter.ardupilot.com/wiki/gps-failsafe/
another "bone": I mentioned that I invoked RTL second time in a row, could it be that APM didn't know at that time where "home" was?
does anyone know why APM could fail to enter a Flight Mode?
I'm very curious why you'd get an error with 9 sats in view. That should be plenty.
this is what I was wondering about too.
Not if they are all in poor positions in the sky
If it can't use them, APM shouldn't count them. How are we to know how many is good? Especially if HDop is good too.
GPS satellites aren't geostationary, so they appear on the horizon, move across the sky, and then disappear over the horizon. A problem occurs as a satellite moves out of view, its signal suddenly degrades and then it disappears. The symptom of this is that the number of satellites will suddenly change and the hdop will increase. Also as the copter flys around, obstacles may interfere with the quality of the GPS signals.
Often there is a sudden shift in calculated GPS position when the GPS device changes satellites or if the signal suddenly degrades. This is usually small but can theoretically be quite large.
I was mostly feeling bad for this guy, nobody was responding to his question, so I tried to start the discussion.
kidding vibrations were 1-2, those big spikes are attitude changes....
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