adamhiram
United States
Offline
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Thank you, this has been very helpful, and the videos in this thread have provided some great explanations of these errors.
I didn't think that's how ATTI mode worked - if I fly indoors with no GPS signal and VPS disabled, it doesn't just go forever when I throttle forward - when I let go of the stick, it throttles enough in the opposite direction to stop and hover. It can't hold its position perfectly and will drift if there is any wind, but it doesn't just keep going until I throttle in the opposite direction to stop it. It makes sense if perhaps the aircraft is unaware it is already moving forward at 30mph when it switches from GPS to ATTI mid-flight and continues drifting, but that shouldn't be the case for any throttle action in ATTI mode, should it?
One thing that caught my attention in the linked videos is when there is magnetic interference on the ground that isn't detected, but the compass is off once in the air. I had an issue with a specific part of my patio that must have a lot of rebar under it, but elsewhere doesn't seem to have that issue. More importantly, it never gets a compass error shortly after take-off. With this flight, it was at almost 400' with 2 pauses along the way to ensure there were no problems. The last time this happened, I had already flown about 1/4 mile away, took some images, and was half way back with a mostly depleted battery before it occurred. At least that time it found a GPS signal before the battery ran out, but it had already flown out of range and had to rely on automatic RTH.
It sounds like avoiding sport mode altogether would help here, or at least result in less severe outcomes in the event of an error, but it's also not really practical. For example, I flew one mission taking images about 1/4 mile away, which is the practical limit for any VLOS flying I can do. Without sport mode, it took almost half the battery just to get there and then obviously I needed to save enough power to get back. Flying in sport mode, I can get there in less than 2 minutes at full altitude, with plenty of time to take images and get back safely. Using only P mode, my range and therefor usefulness of the Spark is pretty severely limited.
Lastly, that preflight check doesn't seem to catch these issues. I always wait for GPS lock, check the number of satellites, and go into settings and check the sensors for any IMU or compass interference before taking off. Admittedly I don't do the thorough take-off checks you mentioned below every time, but again, it's not always practical to take up 1-2 minutes of a 10-12 minute flight with pre-flight checks. That being said, I always hover and maneuver around before ascending, and pause several times to check wind conditions and ensure I still have compass and GPS. This issue is never detected during those checks, and seems to happen for no apparent reason at the worst times. At least this time it was still in transmitter range and I had sufficient battery to make it back, but as I mentioned above, last time it was on an almost drained battery and had already drifted out of range. If it hadn't switched back to GPS mode and initiated a RTH before the battery completely died, it would have been gone.
Thanks again for the insight - I still don't fully understand what caused it or how to prevent it in the future, but at least I have a little better technical understanding of what's happening. I just wish I had more confidence that this will not keep happening until I ultimately lose the aircraft.
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