Twice now on different quads in different places I have had a quad freeze up when it lost GPS signal. I can hear the ground station update to "bad GPS health," and then the quad goes nose down and to the right at high throttle. Quad one I was in auto mode and able to switch modes and regain control Quad two I was not. On the auto mission it was in RTL mode after completing the waypoint sequence. The second quad was in auto tune. I both set to GPS failsafe Land. I am wondering if the issue is something in the failsafe sequence? I don't have logs for the first one, and am waiting for the logs to finish downloading from the second one. But two different quads (qav 500, dji armed spider frame) different gps receivers on each, one with and without remote compass, different motors, and different batteries, but same issue. Anyone else had something similar happen? Or have an idea what is causing this?
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jg, I believe I'm having the same issue you had(http://diydrones.com/forum/topics/crash-out-of-nowhere), but I'm not completely sure. As soon as I armed the quad in stabilize, it shot straight up into the sky and crashed down on my roof. But looking at my logs, I had 8-9 sats so I don't have a clue. Should I just keep geo-fence disabled? It just did me a lot more harm than good.
Before that, we had copters that would go slightly off-level when flying dozens of circles with them (solution: dont't). Now we have copters that depend on fancy satellite signals being clean, or they may become unflyable and crash.
Either there is something I have misunderstood, or it was progress but in the wrong direction.
@jg,
Since I am running a Pixhawk on one of my Slash rovers, I am presently running two uBlox LEA-6 GPSs and have been recording GPS lock performance.
On several occasions the primary 3DR GPS/Compass has lost lock for a second or so while the secondary GPS has maintained a lock.
There is an effort underway for Pixhawk users to be able to take advantage of the two GPS configuration to help prevent GPS lock loss from causing erratic navigation control.
Regards,
TCIII ArduRover2 Developer
I went through the logs and didn't see any error codes. I do have a bunch of recurring ev 15,18, and 28 in the logs. Is this the apm thinking it is supposed to be landing, deciding it had not landed so rearming and trying to land again?
So I dug through the logs and I get GPS-1 error. Then a minute or two goes by and I get GPS-2 error. At the GPS-2 error the APM enters failsafe mode and attempts to RTL because it breached the GPS fence I had turned on. I didn't breach the fence but the new position that first loaded into the APM after the glitch must have been outside my fence. I had it set to 500 feet because I am flying in an area I don't want the quad to go far from. My guess is because it has no idea where it is, or where it is going it falls back to some standard angle hold, or what level is supposed to be without any inputs? The throttle out also pegs at 1000 when failsafe is engaged. I was below the RTL altitude so I assume that means it is trying to get to the 49 feet specified then RTL? My question is if a GPS fault is registered why is the APM relying on a GPS to RTL? Is it the programming currently on it? Why would it not switch to ALT hold instead or not engage failsafe at all? It does not make sense for it to switch to a mode that was triggered by the sensor used for that mode. I verified through HDOP and SAT that I indeed had glitches. I would go from 9 sats to 0, the right back to 9. first time must have not moved the position enough to trigger RTL. Second time it was at 0 sats longer and triggered the GPS fence breach failsafe.
When (not if) GPS fails there is only one sure thing the aircraft can do on its own, which is to land, and one sure thing the pilot can do, which is to take manual control, if the aircraft is in Tx range (if it's not, that's a whole different story...).
Taking manual control effectively means first of all being able to fly the aircraft manually, starting from a perhaps difficult point in regard to distance and orientation. It also means changing from auto to manual mode quickly and without fumbling. Something like forgetting that an autotune switch is thrown is not conducive to a successful save. That touches on the need to do a systematic preflight check of all systems, something that is often skipped over by most of us but that can save a lot of grief.
Bottom line: You are pilot in command at all times. When an automated system fails or glitches, it is up to you to have the skills, preparation and knowledge to recover the aircraft, or at least crash it safely. Maybe one day all of the nifty things auto modes can do will be super-reliable, say like the brakes on a modern car, where you need not be thinking about alternate ways of stopping. But in the meantime you need to be ready and able to take instant control, regardless of how many vendors tell you that all you need to do to become Sky King is push a button.
I know you don't know anything about me. But my piloting skills are not the issue here. I have been flying r/c for 25 years and fly 3d single rotor helis. I tried to save it, but when you are only 25 feet off the ground and something completely unexpected happens you don't have much time to react. I wasn't flying in an auto mode. I was manually flying running auto tune after I had hand tuned enough to get the quad to fly ok. The APM went into an auto mode by itself based on the geo fence I had set up. The auto mode it went into was reliant on GPS for navigation. So it isn't like auto mode when gps fails and you can set auto land or ALT mode. That is my whole point. Why would it go into a GPS guided mode with a GPS failure and not realize it shouldn't be in that mode. I have had this issue with the Geo fence failsafe breech twice with two different systems on two different quads. I turned off geo fence today and even with bad gps health the issue did not happen. I have gps issues around my home because I fly near trees and walls that block the signals sometimes.
I am guessing the reason I could not save the second quad from crashing was because I was in Auto Tune and forgot to switch it off. I don't know if switching modes would override what I think was an auto_land command from the gps failsafe event.
I'm under the understanding that in the event of a gps glitch it is meant to enter land mode.
that may not be correct but was my thoughts