Drifting

[ddodell]

I am a novice pilot.

While flying today, I got to a position I wanted to photograph and noticed the Mavic drifting sideways while hovering.

I was at about 150 feet in altitude, and on the ground, the wind was negligible.

Never have seen this before, usually the Mavic is solid when hovering. I also noticed that I had 20 satellite lock, so that should have been plenty for accurate positioning. I did also check my magnetic settings before takoff.

Any suggestions?

 

[Drone Master]

I am a novice pilot.

While flying today, I got to a position I wanted to photograph and noticed the Mavic drifting sideways while hovering.

I was at about 150 feet in altitude, and on the ground, the wind was negligible.

Never have seen this before, usually the Mavic is solid when hovering. I also noticed that I had 20 satellite lock, so that should have been plenty for accurate positioning. I did also check my magnetic settings before takoff.

Any suggestions?

I would first start off with compass calibration first, then re calibrate the IMU.
Drifting is caused by several factors.
1, IMU needs re calibration.
2, compass calibration!
3, RC stick calibration!
And many others. Carpet versus tile for example.
Have you ever had a minor crash or incident with your Mav?

 

[locoman]

How much was is drifting and does the drifting continue. Sometimes, mine moves around a few inches while hovering, but comes back to the center point, sometimes it hovers rock solid. I think this is pretty normal. It could be what Drone Master said, but the only thing I have done was calibrate my compass and only when I get the message to do so, at startup.

 

[Dragonfly]

GPS, hmm, it doesnt matter how many satalites your Mavic is lock onto, what is important is the HDOP (horizontal dilution of position) of those satalites. Thats the position of where they are in the sky and strength and accuracy of their signal.
The GPS and GLOSNASS Civilian signal has a built in error of upto 15 meters to its center accuracy and it changes around its compass axis regularly.
Ideally we require 3, 4 better sats as high in the sky at different poles for best HDOP, the lower in the horizon the worse the HDOP (the less accurate the possitional information)
Its the HDOP and GPS data from 3 sats 4 for altitude that gives us our position, not how many we are locked onto.
Your GPS unit contains an Almanac of all the sats and where they are at any particular time of day or night and updates this everytime you use your GPS. It uses the Almanac to hotstart and connect to the satalites when you turn on your Mavic and will switch to the best and highest HDOP sats automatically as they rise and fall over your part of the sky.
The problem arises when there is bad data from the sats being used or the sats are not high enough or the HDOP is bad or maybe the Almanac hasnt been updated. Or you have encounted a sunflare radiation hit which interferes with GPS signal if strong enough.
Either way for some reason your Mavic temporarily lost GPS position data and drifted even thou it said it was locked onto 20.
It just says we should not rely on GPS or ground sensors when flying low and learn to fly our aircraft when in atti mode.
Its good to buy a cheap non GPS quad and learn to fly by sticks so one can control or know what to do when automation does not work.

 

[ddodell]

Thank you ... I'll go through recalibration. No crashes or incidents with my Mavic ... it has been a very reliable machine so far.

I've never done a RC Stick calibration. The others I've done a few times since ownership.

I would first start off with compass calibration first, then re calibrate the IMU.
Drifting is caused by several factors.
1, IMU needs re calibration.
2, compass calibration!
3, RC stick calibration!
And many others. Carpet versus tile for example.
Have you ever had a minor crash or incident with your Mav?

 

[ddodell]

Just an update ... I recalibrated the compass, IMU and RC stick ... all rock solid on the last two flights ... thanks for the advice.

 

[BudWalker]

GPS, hmm, it doesnt matter how many satalites your Mavic is lock onto, what is important is the HDOP (horizontal dilution of position) of those satalites. Thats the position of where they are in the sky and strength and accuracy of their signal.
The GPS and GLOSNASS Civilian signal has a built in error of upto 15 meters to its center accuracy and it changes around its compass axis regularly.
Ideally we require 3, 4 better sats as high in the sky at different poles for best HDOP, the lower in the horizon the worse the HDOP (the less accurate the possitional information)
Its the HDOP and GPS data from 3 sats 4 for altitude that gives us our position, not how many we are locked onto.
Your GPS unit contains an Almanac of all the sats and where they are at any particular time of day or night and updates this everytime you use your GPS. It uses the Almanac to hotstart and connect to the satalites when you turn on your Mavic and will switch to the best and highest HDOP sats automatically as they rise and fall over your part of the sky.
The problem arises when there is bad data from the sats being used or the sats are not high enough or the HDOP is bad or maybe the Almanac hasnt been updated. Or you have encounted a sunflare radiation hit which interferes with GPS signal if strong enough.
Either way for some reason your Mavic temporarily lost GPS position data and drifted even thou it said it was locked onto 20.
It just says we should not rely on GPS or ground sensors when flying low and learn to fly our aircraft when in atti mode.
Its good to buy a cheap non GPS quad and learn to fly by sticks so one can control or know what to do when automation does not work.

If you're interested in the GPS info such as HDOP and PDOP CsvView now extracts this info from the .DAT. CsvView can be obtained here
CsvView Downloads

The gpsHealth signal summarizes the HDOP and PDOP values and has a range [0 -5]. GPS+ATTI mode requires that gpsHealth be 4 or 5. gpsHealth will sometimes be set by the FC to be < 4 even though the HDOP and PDOP values are good. I suspect this is done because it's a way to cause the AC to switch to ATTI from GPS+ATTI.