So now that I've flown the Mini quite a few times I've noticed some issues with the compass and barometer of the craft.

The orientation screen hardly ever seems to be accurate, if I don't calibrate the craft compass every single time I take off. This happens even at same places like on my own yard after I switch batteries. Usually it's fixed by calibrating the compass again and its stays good until next power down. Same place with fresh battery and power on -> compass way off. There are no metal or other magnetic disturbances around and I'm 100% sure that the mobile device's own orientation and compass is correct.
I don't know if drifting off compass is causing very inaccurate heading stability, as everytime I try to fly forward in a straight line the craft tends to yaw slightly off course. Same happens also when changing altitude without any yaw/pitch/roll inputs. Heading might also chance slightly or slowly by itself while hovering more than 10m up.
At first I thought this was 'cause of bad props, but I'm on my 3rd set now and still having the unstable heading issue. Since the wandering yaw stays pretty much the same on all three flght modes, I don't believe it's caused by the motors or props.

The other thing is the inaccurate barometer and/or aircraft has brain damage. 99% of the flights I've flown the app is showing negative 4 to 10m altitude on landing, even when landing higher than the take off point. Usually I start my flights on ground from a pad or suitable flat ground (which are scarse at this time of year) but I tend to palm the landing to protect the gimbal and props. Still the app altitude is usually way under the actual altitude, like several meters into the ground off. Tried this again today and after taking off from the ground altitude was correct at about ~2m on my eye level. Took it straight up to 70m and descended back to my eye level and app was showing  negative 9m.
Same thing happened while flying in S under 5m (actual height) and doing aggressive maneuvers, the altitude slowly dropped with every turn on to the minus side while actual height was pretty much the same.

Also noticed that after about 50m horizontal full speed dash at few meters up after letting off the sticks the craft braked, descended on it's own during and after the braking and all the time indicated height was going down also. I don't know if it would had hit the ground since I applied full throttle when it dropped under about 0,3m.
I guess this is related to the sudden altitude losses mentioned in other threads, but WHY does it still descent while already showing negative indicated altitude ON TOP of it's recorded homepoint AND it surely saw the firm ground under it?
This topped off to the fact that while flying under 10m my craft constantly wants to climb while flying forwards, climbing is way worse on S mode, and the opposite it wants to descend while revesing, also worse on S...
Haven't had the time or interest to go through the logs yet, but have to do that sometime soon.

No major issues happened because of these yet (only ruined shots ), but just wanted to find out if these are already documented issues which could be fixed by future updates or do I just have a lemon in my hands?

Also noticed my mini being a little unstable holding its hight. I will test the Barometer myselve ( going up and Down and watching out for negative values)
Cheers

Thanks DB, those are all steps I've already done. Also my device is capable of reorienting it's compass accordingly to match the phones actual orientation (portrait/landscape). Came to the conclusion that RC doesn't have much of an effect on the phone's compass while hiking to a location. So it has to be the AC compass going haywire...
Just would like this resolved so I could get decent material on straight line shots, but if the issue persist I guess I have to return this one.

I get how wind, attitude and such could throw the barometer off, but what I don't get is that the indicated altitude is correct in relation to the AC's actual movements? That would point that the barometer is working correct but the altitude of the craft is still changing, even when it's in range for the infrared sensors to give it the correct altitude. Major brain issues?
Why I thought the barometer was faulty is the totally wrong indicated altitude, but I guess that could also be a firmware/hardware issue...

Miixxa Posted at 1-19 10:34
Thanks DB, those are all steps I've already done. Also my device is capable of reorienting it's compass accordingly to match the phones actual orientation (portrait/landscape). Came to the conclusion that RC doesn't have much of an effect on the phone's compass while hiking to a location. So it has to be the AC compass going haywire...
Just would like this resolved so I could get decent material on straight line shots, but if the issue persist I guess I have to return this one.

So it has to be the AC compass going haywire...
If the drone's compass was the problem, you would have bigger things to complain about.
It's the compass in your phone that's the issue and recalibrating the drone's compass won't ever fix that.

Labroides Posted at 1-19 13:04
So it has to be the AC compass going haywire...
If the drone's compass was the problem, you would have bigger things to complain about.
It's the compass in your phone that's the issue and recalibrating the drone's compass won't ever fix that.

Well if it is the phone's compass then I don't know why it behaves differently while flying. Like I said I tested the phone compass with an actual compass on a hike to a location I wanted to film. No matter what was the orientation of the phone, it continued to indicat true north, even when attached to the powered on controller...
But have to test some more I guess.

And the AC compass isn't going all 180degrees out like in some cases here. Instead it seems to gradually slip out of alignment few degrees at a time. I can't think of another reason why the yaw is drifting on it's own and why the alignment is off for several tens of degrees after each power-on.

Do you have a smartwatch? Also is your device in airplane mode?

Miixxa Posted at 1-19 13:19
Well if it is the phone's compass then I don't know why it behaves differently while flying. Like I said I tested the phone compass with an actual compass on a hike to a location I wanted to film. No matter what was the orientation of the phone, it continued to indicat true north, even when attached to the powered on controller...
But have to test some more I guess.

As Dirty Bird said, try calibrating your phones compass while it is attached to your controller. There are metal parts in the controller that can influence the compass. The compass in the aircraft has nothing to do with thissue, it can be miles away and having no effect at all.

As to the barometer issue, Dirty Bird is correct again, it is probably pressure variations in the barometric sensor. Barometers are not particularly accurate, never have been in the history of aviation, which is why the full size ones can be udjusted. You should never rely on them for accurate height measurement, which is the reason why DJI put sensors on the bottom of the aircraft to measure ground proximity.

deathsquad Posted at 1-19 13:24
Do you have a smartwatch? Also is your device in airplane mode?

Nope and yes.
Didn't even have a belt in my trousers or metal buttons on my jacket..that's how paranoid I was.

And @Geebax, thank's for your input but could you have at least read all three of my comments...

It might be interesting to know how that incorrect measurement might affect RTH altitude. Also I need to verify that RTH altitude can be set during flight without altering the home point.

If I alter the HP during flight I get noticed about the RTH altitude being updated, unlike when I just modify the RTH altitude alone.

m80116 Posted at 1-19 16:40
It might be interesting to know how that incorrect measurement might affect RTH altitude. Also I need to verify that RTH altitude can be set during flight without altering the home point.

If I alter the HP during flight I get noticed about the RTH altitude being updated, unlike when I just modify the RTH altitude alone.

Well I can answer that, it affects it just like you would think. Luckily it tends to be off to the negatives, so it just makes the actual RTh height even higher than set height.
Tested this by flying next to a tree top, looking the height and setting the RTH on the height of said tree, did some flying and activated RTH to return just by that same tree. Just eyeballing it the RTH height was about 6-8m higher than the tree.
Imagine the problems if the indicated height would go off in the other direction...

And then there is this.  

Miixxa Posted at 1-19 13:19
Well if it is the phone's compass then I don't know why it behaves differently while flying. Like I said I tested the phone compass with an actual compass on a hike to a location I wanted to film. No matter what was the orientation of the phone, it continued to indicat true north, even when attached to the powered on controller...
But have to test some more I guess.

The phone compass issue has been already discussed in many posts.

You can check this on your own: it's not a problem of phone compass (you duble checked with an hand held compass and the 2 readings are coherent), but is a deviation due to some magnetic stuff inside the RC. If you just turno on your phone compass and the you move your compass toward thr RC (even if its switched off), you'll notice that the readings on the phone screen will be severely affected when your phone si close to the RC.

Hints: clamp your phone on the RC and then make a cell phone compass calibration: it should be fine,

As per barometer issue, they just measure air pressure variations which occurs whenever you change your altitude above sea level (or ground level).

But I remember as well that barometers, once upon the time, where used for weather forecasts, as the atmosferic pressure is a proxy of weather conditions.

Finally, bear in mind that a barometer is thermally sensitive: you should adjust the zero when is in thermal equilibrium with the environment where the measurement is carried out. I wonder if such errors are due to the fact that when you begin your flight, mainly in winter time (and moreover in Finland), your AC and its inner parts may be still at home temperature when you take off.

Someone suggested in this forum the store your drone in a refrigerator before leaving for a flight; it may be too much, but definitely having your drone in thermal equilibrium with the environment is fundamental.

Of course by means of electronics you can thermally compensate whatever you want; I don't know if DJI designers and engineers did it...

Thx emaneg!
This is starting to feel like banging my head to the wall, cause I've literally tested everything, even many things not mentioned here yet. Maybe I should take a video for you guys to demonstrate that the RC doesn't affect my device at least not in a way that's detectable...And even if it did, it's not gonna cause the unstable heading of the AC.

I know what barometers are and how they work, I've also wondered how an instrument that's basically just doing predetermined guesswork can work so well f.e. in cheap toydrones I have. But the altitude hold seem to work "fine" on 40dollar drones even when it has no other means of knowing it's height than the barometer alone. So why is the altitude hold so imprecice on a drone that costs ten times more and has dedicated additional height sensors...

The temperature difference is a great point, and like we see on the forum it can cause other issues also. I usually don't have issues with acclimation, since I mostly to do my flying in places that require exposing the drone to cold while getting there. I'd say that the drone would acclimate properly in flight, but I'm still getting same issues after 15-20mins in the air. Mini tends to generate lot of heat inside the craft so I don't know if that could mess with the instruments? But it's a valid point and I need to test if a longer "cold-treatment" before flight would help...