Hi,
I'm very new to drone world, so please forgive if this is stupid question.

After several times outside I tried my Mavic indoor (big empty space)
First time I didn't have any problem. Light was sunlight from multiple windows but I don't rememeber if drone was in opti mode or atti mode.
Second time, yesterday, I was in artificial light condition (maybe too low), drone entered in atti mode. As soon it took off it began to fly backwards. Immediately I landed it (while flying backwards). I've recalibrated the compass then tried twice with same results.
I know that in atti mode the drone continue to fly in the same direction also when the pilot release controls but I just do the take off command.
Today I tried outside GPS mode, no problem. Then tried again indoor in ATTI mode with same results.

My question is what I have to calibrate to solve this problem? And how? I tried to find something about Atti mode in user manual but I didn't find any useful info about it except you have to flight with caution.

There is no calibration for Atti mode, when your bird loses GPS in Atti mode it just drifts with the wind, you need to learn to correct the drift with your sticks. All pilots should learn to fly Atti for those regular times when you will lose GPS. It is just practice but unfortunately you can't manually select Atti on the Mavic at the moment. I hope DJI make an update to make Atti selectable  in the settings.

Jimney Posted at 2017-1-10 10:14
There is no calibration for Atti mode, when your bird loses GPS in Atti mode it just drifts with the wind, you need to learn to correct the drift with your sticks. All pilots should learn to fly Atti for those regular times when you will lose GPS. It is just practice but unfortunately you can't manually select Atti on the Mavic at the moment. I hope DJI make an update to make Atti selectable  in the settings.

There is no "ATTI mode calibration," but if I understand things correctly, the aircraft's stability in ATTI mode (not counting the effect of wind) would be affected by the IMU, wouldn't it? So then, would a proper IMU calibration possibly lead to more stable ATTI mode flight?

A glass of vino should help calibrate for ATTI mode.  

Jimney Posted at 2017-1-10 10:14
There is no calibration for Atti mode, when your bird loses GPS in Atti mode it just drifts with the wind, you need to learn to correct the drift with your sticks. All pilots should learn to fly Atti for those regular times when you will lose GPS. It is just practice but unfortunately you can't manually select Atti on the Mavic at the moment. I hope DJI make an update to make Atti selectable  in the settings.

Thanks for clarification but I was indoor, so no wind!!!
I repeat to clarify. I was in ATTI mode, as soos as I took off  (no other input to RC) Mavic started to fly backward.
Should I need a controller calibration if in GPS mode everything is ok?

donachy78 Posted at 2017-1-11 06:54
Thanks for clarification but I was indoor, so no wind!!!
I repeat to clarify. I was in ATTI mode, as soos as I took off  (no other input to RC) Mavic started to fly backward.
Should I need a controller calibration if in GPS mode everything is ok?

I believe in ATTI mode, it can drift anywhere because the IMU only used the barometer to try to knows the altitude.  Anything could affect the movement such as propeller unbalance, etc.  If you fly a cheap drone, you will exactly knows things are unpredictable.

fai58 Posted at 2017-1-11 12:19
I believe in ATTI mode, it can drift anywhere because the IMU only used the barometer to try to knows the altitude.  Anything could affect the movement such as propeller unbalance, etc.  If you fly a cheap drone, you will exactly knows things are unpredictable.

Ok,
so, if I understand, you are telling that this behaviour is normal, isn't it?

It needs  to be about a meter or more above the floor.

donachy78 Posted at 2017-1-11 06:54
Thanks for clarification but I was indoor, so no wind!!!
I repeat to clarify. I was in ATTI mode, as soos as I took off  (no other input to RC) Mavic started to fly backward.
Should I need a controller calibration if in GPS mode everything is ok?

Wind exists indoors!

To be more clear:  There are MANY wind currents that exist indoors due to HVAC systems, thermal "hot-spots" or "cold spots" (like windows) and then the drone itself.  Just the act of cycling air (cooling OR heating air) pushes air throughout a room from a source to a return.  Add heat to that and you have up-drafts, add cool to that and you have down-drafts.  Even without any HVAC running and in a room without windows, the drone itself creates a downdraft of air that has to go somewhere.  When it hits an obstacle, it will create a change in direction and that can push the drone around.

So, drifting is pretty much GUARANTEED when flying indoors without any GPS or OPTI stabilization.  It is my understanding that OPTI mode can assist you from moving around IF the surface of the floor is not overly reflective and IF you have enough ambient light.  About the most you can count on from the Mavic is a steady altitude, and even that will change as conditions change in the room.

If there is no wind affecting the drone you could reasonably assume the drone would hover pretty much in the same place, with small inputs on the sticks for minor correction. However, as has been pointed out to you, there will be contributory factors that will influence the drone. Ground effect will build a cushion of air under the drone much like trying to balance something on an upturned bowl. The higher off the ground the lesser the effect, say four feet should be much easier. Convection from hot and cold areas will play their part but I assume from your description that this seems to be more acute than that. Prop or weight imbalance will play their parts too, so check the props look clean and you haven't stuck anything on the drone like an extra camera for example. The only thing left to do would be to calibrate the controller. It's the most likely cause from the description you have given that could cause such an imbalance if all else is ok.
Without doubt, the best way of experiencing unaided flight is the use of a cheap small indoor drone. Once you can fly the thing forwards and backwards, left and right and lastly, and probably the most difficult, nose in, then handling the Mavic will be a piece of cake.

I'd like to get some clarification on something that a couple of people have mentioned above... Should unbalanced props or other weight imbalances really affect the aircraft's stability, even in ATTI mode? My understanding is that the IMU, if properly calibrated, can always tell the aircraft whether it is level or not. So, if there's a weight imbalance causing the aircraft to tilt one way when all four motors are spinning equally, won't the IMU recognize the tilt and apply corrective measures to the motor controllers? That would be my understanding, but I may be completely wrong.

BTW, I realize that the craft can and will still drift due to other factors, but it should remain level, shouldn't it?

Gary Mac Posted at 2017-1-12 07:30
Wind exists indoors!

To be more clear:  There are MANY wind currents that exist indoors due to HVAC systems, thermal "hot-spots" or "cold spots" (like windows) and then the drone itself.  Just the act of cycling air (cooling OR heating air) pushes air throughout a room from a source to a return.  Add heat to that and you have up-drafts, add cool to that and you have down-drafts.  Even without any HVAC running and in a room without windows, the drone itself creates a downdraft of air that has to go somewhere.  When it hits an obstacle, it will create a change in direction and that can push the drone around.

Ok,
generally you could be right but I mean there wasn't any kind of wind currents that could cause this behaviour of drone. It starts to fly backward very fast, not just drifting!!!

I think that rick39 could be right about controller calibration.
Now my drone is in care at the DJI for a camera flare problem. I ask them to check also this behaviour. AnywayI will try as soon I will get it again