Where is the drone? Said my GPS.

[Noremac]

So today I decided to do a test.
I started the Mavic, took off to an elevation of about 4 feet and hovered. My goal was to leave it there until it auto landed due to low battery.
I wanted to see just how much battery life I can get. I got 21 minutes out of it and assume with the remaining 10 percent I might have got a couple more, getting close to the advertised 27 minutes. It was in normal mode with low noise props installed. Honestly a little disappointed with the life I got. Was hoping to get closer to 27. Oh well.
The interesting part of it was where the gps said it was during the hover. Before I took off it already said it was 4.7 feet away from the home point. During the hover not touching the sticks at all it said it moved a max of 25 feet away from the home point and continuously changed throughout the test. Elevation stayed rock solid at 3.3 and the vps toggled between 3.6 and 3.9.
Once again, I took off to about 4 feet and hovered until battery auto landed at ten percent. Didn’t touch the sticks once and the distance from home kept changing with a max of 25 feet.
I did watch until complete. Other than minor corrections to keep itself on point it did not move at all.
Another interesting point is that the flight log said a total flight distance of 359.8 feet.
Hmmmm? I wonder why it did this. Is it normal? What might be able to be done to fix it?
Thanks for hearing my rant.

 

[lisadoc]

How many satellites of reception did you have? That can make a big difference in accuracy.

 

[Noremac]

How many satellites of reception did you have? That can make a big difference in accuracy.

Sorry. I meant to throw that in there. During the test I had between 10 and 15 satellites.

 

[Phxbird57]

So today I decided to do a test.
I started the Mavic, took off to an elevation of about 4 feet and hovered. My goal was to leave it there until it auto landed due to low battery.
I wanted to see just how much battery life I can get. I got 21 minutes out of it and assume with the remaining 10 percent I might have got a couple more, getting close to the advertised 27 minutes. It was in normal mode with low noise props installed. Honestly a little disappointed with the life I got. Was hoping to get closer to 27. Oh well.
The interesting part of it was where the gps said it was during the hover. Before I took off it already said it was 4.7 feet away from the home point. During the hover not touching the sticks at all it said it moved a max of 25 feet away from the home point and continuously changed throughout the test. Elevation stayed rock solid at 3.3 and the vps toggled between 3.6 and 3.9.
Once again, I took off to about 4 feet and hovered until battery auto landed at ten percent. Didn’t touch the sticks once and the distance from home kept changing with a max of 25 feet.
I did watch until complete. Other than minor corrections to keep itself on point it did not move at all.
Another interesting point is that the flight log said a total flight distance of 359.8 feet.
Hmmmm? I wonder why it did this. Is it normal? What might be able to be done to fix it?
Thanks for hearing my rant.

that is interesting. today I took my Mavic out for a long flight. I ended up having to auto land about 9000ft away. When I was landing I seen a dirt road so I new I could drive there. the funny part I got the long & lat from my phone typed it in and want and found my drone. after getting home I was looking at the video which had stopped about 600 from where it landed. I started looking at the Long & Lat from my data file and it was off by 368 ft. and I rechecked the Long & lat from my phone and it eve was 36 ft off. close enough to fine it. I had 17 to 18 sat count. at the end.

 

[BossBob]

Civilian use GPS is prone to a little wandering of the reported position. There is an Android App called GPS Averaging which can show the error and average out the reported positions. While writing this email my phone, with 21 satellites in view, and 12 in use, I was getting an accuracy error of 6 metres.

 

[Noremac]

Civilian use GPS is prone to a little wandering of the reported position. There is an Android App called GPS Averaging which can show the error and average out the reported positions. While writing this email my phone, with 21 satellites in view, and 12 in use, I was getting an accuracy error of 6 metres.

Thank you for the info. I don’t recall this ever happening in the past. At least not while I was paying attention to it. So I figured I’d throw it out there to see what may be different this time vs others.

 

[Ping^Spike]

The Mavic doesnt support RTK mate, you're going to get variations

 

[BossBob]

By the way, your Mavic was probably using its visual sensors to hover in place at 4ft in the air so the whole of the “flight” was probably due to the lack of accuracy of the position of each individual gps fix leading to a spurious track.

 

[MariusF]

That's the point.. GPS in combination with the visual systems gives you a pretty stable position over ground.
But the distance travelled might be just from GPS - including errors.

Not getting the 27 minutes out of your battery might be because of just hovering.
As far as I remember the best aerodynamics and therefore best battery usage is while in continuous forward flight.

 

[BossBob]

Agree with the previous post. At 4ft there is plenty of room for a downward flow of air to set up underneath which would cause the Mavic to have to work harder to stay at the set height. The Mavic, and any other rotary winged aircraft, needs to be moving on to a fresh cushion of still air to get the most lift.

 

[FearlessRobb]

That's the point.. GPS in combination with the visual systems gives you a pretty stable position over ground.
But the distance travelled might be just from GPS - including errors.

Not getting the 27 minutes out of your battery might be because of just hovering.
As far as I remember the best aerodynamics and therefore best battery usage is while in continuous forward flight.

I believe hes roght with the 27 min if ita only hovering you get 20-21. 24-27 if flying. Not sure how ot works but thats also prime conditions that do not effect drone at all

 

[Noremac]

TThanks for all the info everyone.

 

[Exphantomflyer]

Side track, did I hear right, 27 minutes of flight ?

This I have to test, so what's the best speed to be doing to hit 27 minutes ?

 

[Kilrah]

The 27 "marketing minutes" you can only achieve in conditions that you're never going to encouter ever (supposed to basically be flying at optimal efficiency speed continuously with a brand new battery at sea level until a second before it falls to the ground due to low battery shutdown at 0%...)
20-21 is typical of normal flying and safe margins.

 

[Floater]

Min power speed is about 20 mph. Best range speed is about 30 mph. Hover requires about 95 W, 85 - 90 W at min power speed. The min power speed is pretty broad, seems to be on the data scatter from ~15-25 but rapidly escalates from there. The rather high drag configuration is expensive (power-wise) at higher speeds with about 180 W needed to approach 40 mph.

 

[Exphantomflyer]

The 27 "marketing minutes" you can only achieve in conditions that you're never going to encouter ever (supposed to basically be flying at optimal efficiency speed continuously with a brand new battery at sea level until a second before it falls to the ground due to low battery shutdown at 0%...)
20-21 is typical of normal flying and safe margins.

Well I did a test from 100% to 10% autoland, flying at full speed all the time and managed 26 minutes 11 seconds, so I guess 27 minutes would be achievable.

 

[Floater]

Well I did a test from 100% to 10% autoland, flying at full speed all the time and managed 26 minutes 11 seconds, so I guess 27 minutes would be achievable.

Sport or position mode?

 

[Exphantomflyer]

Sport or position mode?

Standard mode, averaged about 20mph all round

 

[f3honda4me]

Just a quick note, That close to the ground the drone is being held in place on all axis by the VPS.

 

[Jacknet007]

I got over 27 minutes. Flew around till critical low battery and then hovered 2 feet off the ground till battery was at 1% and landed. But it's not recommended to do that. I try to land with 20% to 30% left in the tank.