Minor drifting?

[diggs]

I've got a question, when my drone is just hovering (no stick inputs) it drifts in the air a little bit (sideways and up/down). Pretty small values but maybe 30cm in total. Both outside with no wind and inside too. This is a replacement MM and I don't seem to recall this kind of drifting the first time?

Is that normal? Could it be a prop issue?

Can post logs if that is relevant...

[EDIT] who am I kidding, logs always add value so posting 'em

 

[lannes]

Was the MM hovering in bright conditions ?

According to the specs the hovering accuracy is:

Vertical: ±0.1 m (with Vision Positioning), ±0.5 m (with GPS Positioning)
Horizontal: ±0.3 m (with Vision Positioning), ±1.5 m (with GPS Positioning)

So it appears to be in spec

 

[Starz]

Normal based on what I’ve seen with the one I have. Can’t expect p4p performance out of a pint sized mavic.

 

[diggs]

Yeah, just seemed quite a bit more than my previous MM, so wasn't sure if I was imagining that or if other people were seeing the same thing. One more question, when you rotate the MM, do you find the drone flights in a bit of a circle, or stays in the one position pivoting in the same spot? I could swear my old MM would pivot on the spot, whereas this version ends up spinning in a small circle...

 

[new2mavic]

My Mini is as solid as my M2P when hovering indoor even after a big crash breaking the gimbal into several pieces.

 

[new2mavic]

In your flight log, the number of GPS is very small ( around 6 compared with 15 ~ 20 in good conditions ) so the position accuracy cannot be expected to be good.

In the first half of the flight , positioning was done visually with the camera at the belly. It will work well only if the camera lens is clean, lighting is good and the camera is looking at scenes with with high-contrast features. Suggest to try again in environments where all these criteria are met.

 

[slup]

Nah ... let's make this a bit more scientific now when logs are included ? ... let's see if we can find anything going outside the specs.

This can be good to know looking at the graphs further below ... (rotation arrows indicate positive direction)



Then so we know the circumstances ... the attached log is from a flight with a navHealth between 0-2, meaning no GPS lock, just VPS holding the position.

And the spec as quoted earlier:

Vertical: ±0.1 m (with Vision Positioning), ±0.5 m (with GPS Positioning)
Horizontal: ±0.3 m (with Vision Positioning), ±1.5 m (with GPS Positioning)


First looking into the height accuracy from a spot in the log covering roughly the first minute ... (click on the chart to make it larger)

Black = Z speed (ascend/descend)
Blue = Throttle stick input (max/min, 10 000/-10 000)
Yellow = VPS height in meters

Conclusion: No uncommanded height change above spec occur, all ascends & descends are commanded by throttle inputs.



Then something little to check the OP's info about flying in a circle not just pivoting when yawing ... and position accuracy in the horizontal plane (X & Y axis)

Blue = Yaw angle ( note 180/-180 degree axis)
Light blue = Rudder stick input (max/min, 10 000/-10 000)
Green = Aileron stick input (max/min, 10 000/-10 000)
Black = Elevator stick input (max/min, 10 000/-10 000)
Purple = X speed (forward/backward)
Yellow = Y speed (right/left)

As seen during the commanded rudder input mainly no X or Y speed is recorded ... just a very short blip with 0,1m/s right movement were the marker are in the chart but all within spec & a nice pivoting yaw movement.



Then a little later into the flight ... now with navHealth 2, but still no reliable GPS positioning just VPS hold.

Again initiated yawing by means of rudder command then in the middle only elevator inputs which makes the X & Y speeds increase a bit ... then again only yawing by means of rudder command.



Conclusion: No uncommanded horizontal movement above spec occur, all position changes are commanded by elevator or aileron inputs.

 

[new2mavic]

For your reference this is my Mini hovering over a 22cm x 28cm magazine. Indoor, no wind, no GPS, moderate lighting, hands off the RC. The gimbal is not working because it was shattered into several pieces in a recent crash but the camera survived. The horizontal drifting seems to be significantly less than 30 cm. There is no visually discernible drifting in height.

 

[m80116]

If you're quite shielded from direct GPS signal, like in a gully or under trees that is quite normal, especially if VPS is fooled by water or out of range.

The problem lies in the MM basic drone logics... it sticks to GPS when it isn't that good anymore (since there's no Flight mode w/out it, except ATTI when GPS is completely lost), a good choice for beginners but no so much when you want precise control of the framing and path. Be careful when it does so... I think it is wise not to fly under those circumstances.

 

[DanMan32]

None of the DJI quads provide means of turning off GPS and leaving VPS. I wish they would since that would be ideal for indoor flights where GPS might cut in and out.

MM will have some deviation, as long as it stays pretty much centered in one place. It shouldn't circle though if just yawing, except for the above mentioned deviation.

Perhaps recalibrate IMU and compass. Some have found replacing props improved stability. If replacing props, be sure screws are perfectly in place.

 

[diggs]

Thanks everyone for your replies and @slup for the analysis - it's such a thing of beauty and good to know my baby is within specs. The logs were from flying inside (and nice and bright), so it was relying on visual positioning rather than GPS, but always appreciate the feedback re: sats @new2mavic and @m80116 as I learned that lesson the hard way after having a crash with my first drone and then started researching what I should be looking out for in being a new pilot!

I wonder if I had somehow imagined the previous MM was more stable, as I've been out multiple times now with this new MM and it's taking footage/flying fine. @DanMan32 , yeah it's helpful to know what the standard deviation is for yawing and haven't had to change the props yet. Will make sure to focus on the screws placement when I do inevitably have to!

Love this community and very much appreciate all the feedback.