Height calculation - ATTI/Cinematic Mode

[sssoaring]

Hey Guys,

First time poster, please accept apologies if this isn't supposed to be here.

I got a new Mavic Mini recently and absolutely loving it and flying it around taking heaps of pictures. I was recently doing some experimentation and was flying it indoors (had the prop guards on thankfully ?).

I had some low light conditions where the drone would go into ATTI mode from time to time and controlling it wasn't an issue. The issue i faced was once when i was flying on top of my snooker table. It was mostly doing ok, but there was one point where the drone just randomly started powering up and kept climbing. Even though I held full down stick, it stuck to the ceiling and wouldn't come down. I was flying it quite high but about 20-30 cm below below the ceiling, and then it randomly decided to go up by itself. I'm not sure whether it was because of going from ATTI mode to Cinematic mode and not having enough variations in the snooker table from the downwards facing camera for it to think its low and climb or whether there may have been something else at play.

Luckily I had my prop guard on and i went and had to pull it down from the roof myself. Only after i pulled it down for a few seconds with down stick did it decide to turn off. I'm just trying to figure out what may have happened (unfortunately not enough information in the logs) and whether I might be missing something. I just don't want it flying away from me out of control when outdoors. Just wanting to understand how it works a bit better. I've heard a lot about flying it over water, but based of practical experience, has anyone found anything when flying over other smooth surfaces??

Thanks very much!!

 

[sar104]

Once it gets close to a surface above then the air flow into the props is going to pull it in - that's completely expected. If the question is why did it ascend to near the ceiling in the first place then that's harder to answer.

 

[scro]

When flying indoors there are 3 sensors that feed in to the position keeping control system:

1. barometer, for height
2. Optical flow sensor, for horizontal movement. This works a bit like an optical mouse
3. IR transmitter/receiver, for sensing proximity to the floor/objects and possibly also height.

The optical flow sensor needs some detail/contrast in whatever is below it to sense movement so may not see anything if above a snooker table other than flat green. This should only affect lateral position holding, not vertical. It isn't clear exactly how the IR sensor and barometer work together for altitude, particularly without GPS. Indoors, the barometer could be affected by doors/windows opening and closing, and draughts as these will affect the air pressure in the room. The IR sensor could be affected by transparent, very reflective and very non reflective objects, in a similar way to when flying over water.

 

[sssoaring]

Ok. Brilliant. Thanks for the explanation guys!

Just out of curiosity, does it also use GPS for altitude outdoors??

 

[sar104]

Ok. Brilliant. Thanks for the explanation guys!

Just out of curiosity, does it also use GPS for altitude outdoors??

Current understanding is that the FC doesn't use GPS altitude for flight control, but it does log it in the DAT files and put it into the EXIF data for photos.