Sudden movements forward and sideways

Andrew F · Jan 11, 2017

I was just trying to fly in a very snowy scene and my Mavic had two very sudden movements that startled me. I recovered but have retired inside to write this thread.

I started in ATTI / Vision mode under my porch cover with very little GPS signal. I then moved it out to get full GPS signal. It seems to me that right when it got full GPS signal, it suddenly and very quickly shot straight back at me. I had to apply quite a bit of forward stick to stop it from hitting me.

I stopped and restarted and tried again. This time it darted 90 degrees to the right - as if full right stick - for 1 second / maybe 10 feet. Pretty startling again.

I brought it back in, turned off all visual and downward systems and went full ATTI. No sudden movements this third attempt but even after acquiring full GPS (14 sats) and it automatically setting the home point, I was still getting a LOT of drift (3 feet a second and elevation changes), so I called it a day.

Has anyone gone from no sat signal to strong signal and experience what I've just had happen? Am I missing something obvious? My Mavic and battery were both warm. Might the temperature differential have caused the misbehavior? I won't try the ATTI to GPS approach again if that is a known trouble spot. I might try letting the Mavic cool down a bit before flying and see if that makes a difference.

Wacker2611 · Jan 11, 2017

I've heard a few similar stories to this, and not all ended up as happily as yours did! This is pure conjecture, but there is usually a common theme - that is, taking off before you've got a proper gps lock. Again, probably an urban myth, but the compass is intrinsically linked to the gps and you also might have been getting some magnetic interference in your porch?

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Andrew F · Jan 11, 2017

Wacker2611 said:
I've heard a few similar stories to this, and not all ended up as happily as yours did! This is pure conjecture, but there is usually a common theme - that is, taking off before you've got a proper gps lock. Again, probably an urban myth, but the compass is intrinsically linked to the gps and you also might have been getting some magnetic interference in your porch?

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Even if I was getting magnetic interference in the porch, once I got out and in the clear, that shouldn't have mattered - in my mind. I'm thinking the two darting behaviors were from the visual system getting confused by the snow and no details - but I can't imagine the programmers thinking such sudden movements made sense. Once I got full GPS, I expected normal behavior but clearly didn't have it. I'm wondering if the temperature differential was messing with the barometer. I'm going to try again but let the mavic acclimate a bit more to the ambient temperature and then use a landing pad in the snow and see if when I have full GPS it acts normal. If not, then I'll start the recalibration dance I guess.

Jixxer · Jan 11, 2017

My Mavic gets weird if I don't let it find all the sats before takeoff. I have started mine inside the house with only 3 sats, ( in other words Atti Mode ) once outside it picked up 8 more but still was not completely stable until I land and shutdown motors. After restart And home point initiated everything OK ..

LakeTravis · Jan 11, 2017

I can't speak from too much experience with taking off with the Mavic with just a few, or no, satellites. I learned way back in P2 days that (back then, before they used GLONASS sats) you should wait for at least 6 or 7 sat locks. Now I almost always have at least 10 or more. Sometime in the past, I started taking off and would just let whatever quad I was flying go up to about 6' and hover, making sure it is stable, spin it around once or twice, and then start with whatever I intended. Kind of like a (post) run-up in a plane to make sure all is good.

I have read quite a bit about Vision positioning being confused by whatever is below it that has no detail. Seems like snow would be a problem for it, especially when GPS is weak.

Last, but not least, I know that DJI, and everyone else says you don't have to calibrate the compass unless the system tells you to. But they used to tell you it was a good idea, it became a habit, it can't HURT to do it as long as the calibration is successful. I still do the dance, every time.

Andrew F · Jan 11, 2017

Thanks, for the input. I'm pretty sure the sudden movements were due to the vision system. Of course I didn't expect it to work well over the snow - actually I didn't expect it to work at all - but I was shocked at the sudden jerking motions. Those definitely fall in the "not good" category. I started the Mavic out in the open with the normal number of sats (I too usually wait for 10+) and it flew and acted perfectly so I am going to say starting with no or few sats and then gaining the sats is NOT as good as starting with sats. I figured (apparently wrongly) that once it had a bunch it would be happy. Not so today anyway. Cheers!

LakeTravis · Jan 11, 2017

Andrew F said:
Thanks, for the input. I'm pretty sure the sudden movements were due to the vision system. Of course I didn't expect it to work well over the snow - actually I didn't expect it to work at all - but I was shocked at the sudden jerking motions. Those definitely fall in the "not good" category. I started the Mavic out in the open with the normal number of sats (I too usually wait for 10+) and it flew and acted perfectly so I am going to say starting with no or few sats and then gaining the sats is NOT as good as starting with sats. I figured (apparently wrongly) that once it had a bunch it would be happy. Not so today anyway. Cheers!

That's kind of what I was getting at, but looking back to my last post, I guess I left out the part that would have said--I took off with only a couple sats and the Phantom 2 went "bat $hit crazy", I thought it was going to fly away and never be seen again, but I managed to keep an eye on it and get it to land. Some lessons you learn for free--others, not so much!

Andrew F · Jan 11, 2017

LakeTravis said:
That's kind of what I was getting at, but looking back to my last post, I guess I left out the part that would have said--I took off with only a couple sats and the Phantom 2 went "bat $hit crazy", I thought it was going to fly away and never be seen again, but I managed to keep an eye on it and get it to land. Some lessons you learn for free--others, not so much!

Yeah. A bit disappointed with the chaotic movements but lesson learned.