I take a lot of post-sunset long exposure timelapse, which means the aircraft needs to stay in the same position for 15 minutes or more.  The Mavic does GREAT at this as far as holding horizontal position (even with wind!), but not so great in holding a precise altutide.  

At times it does a good job, but recently it drifted up and down as much as 3 feet, which ruined the timelapse.

I usually have to downward sensors turned off so I can do hand-catches, but does this affect altitude hold?  I read in one of the spec sheets that sonar is used for altitude hold, which left me wondering.  If turned on, would a person or car travelling under the aircraft cause it to rise? Is there anything else that affects this?

Thanks for any insight!

The sonar sensors only work when close to the ground - i believe within 10m from ground. Turning them off will not affect the drones stabilisation at all if you are higher than that. As for drifting up and down - yep i noticed that on occasion too - do not know why but i think perhaps whilst hovering as the weather passes over it there may be slight ups and downs in barometric pressure which may cause the drone to think it is a bit higher or lower and make adjustments accordingly. - so it could be the result of environmental conditions.

Bekaru Tree Posted at 2018-1-26 12:52
The sonar sensors only work when close to the ground - i believe within 10m from ground. Turning them off will not affect the drones stabilisation at all if you are higher than that. As for drifting up and down - yep i noticed that on occasion too - do not know why but i think perhaps whilst hovering as the weather passes over it there may be slight ups and downs in barometric pressure which may cause the drone to think it is a bit higher or lower and make adjustments accordingly. - so it could be the result of environmental conditions.

Thank you for the reply.  

I'm my most recent (and worst problem with elevation hold), I was at about 10 meters, over a parking are next to a street as cars slowly passed by (low speed limit) and downward senors were off.   It drifted vertically about 3 feet and back to start elevation about 4 times within 15 minutes, which is far too fast to be a weather condition, I think.   

Perhaps it was picking up passing cars... but my sensors were off, so I'm really confused as to why this happened.

SanDiegoAir Posted at 2018-1-26 13:26
Thank you for the reply.  

I'm my most recent (and worst problem with elevation hold), I was at about 10 meters, over a parking are next to a street as cars slowly passed by (low speed limit) and downward senors were off.   It drifted vertically about 3 feet and back to start elevation about 4 times within 15 minutes, which is far too fast to be a weather condition, I think.   

GPS isn't that accurate near the ground. Try turning back on the VPS (you can disable "Landing Protection" for hand catching).

May be tripod mode ????

If the drone drifting not because of wind speed then "IMU" calibration is needed.

VPS is not effective at altitudes exceeding 15M AGL - the precision at higher altitude is controlled by GPS. Calibrate the IMU before your next flight and try again in lighter wind speeds.

Under the conditions you mention, Mavic uses the built-in barometer. The ability to keep the same height can be read here: https://www.dji.com/mavic/info#specs  under "Hover Accuracy Range". As you can see, the heigth variation seemed to be within spec. If you want to avoid and destroy your timelapse, you must either turn vision on or raise Mavic's height so you can not see the height difference on your timelapse.

Regards Leif.