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QuickStop test
557 26 2-14 05:17
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JJB*
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Hi,

Did some testing with my MM ; fly forward/backwards in Sport mode and with 100% stick (approx 10 m/s) and release stick at once.
I did the test max fwd + relasing stick and max aft + releasing stick.
Situation : no wind (covered area), flying at approx 1.5 meter height above good reflecting surface.

What did i see ; fly height did not change during increasing speed, at stick release MM did climb and slowly returned to fly height.
What did i see more ; flying backwards full speed to a stop ; not as much climb than quick-stoppend from forward flight.

What does the flight log shows : baro height indication shows a up and down dip, VPS height does show the reality.

Shall i do this flying low above water?  uhh, not sure about that  ;-)



cheers
JJB





Quickstop.png
2-14 05:17
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ALABAMA
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Good testing!
2-14 05:28
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Woe
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Great test.
2-14 06:11
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Mortensldk
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Good Test.
2-14 07:08
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TDZHDTV
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Always interesting to review your tests, if you repeat test flying into wind I’m confident your Mini will climb and not correct itself, Maybe you could try?
2-14 07:42
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JJB*
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TDZHDTV Posted at 2-14 07:42
Always interesting to review your tests, if you repeat test flying into wind I’m confident your Mini will climb and not correct itself, Maybe you could try?

yes, next week i have some time to do more tests.

2-14 07:46
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Sigmo
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Thanks for doing this for us.  
2-14 07:49
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InspektorGadjet
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Good tests JJB,
Now the million dollar question, what if you are out of VPS range, say 10m or higher?
All the situations where my mini did this climbs and drops was from flying within VPS range (backyard), to a lower terrain (downhill) so by the end of the travel the mini was way over VPS range...
I wonder if that has some effect.

Also, my flights were around 100-150m distance, so if the "errors accumulate" it could explain higher climbs or drops.
Thanks again for the tests.
2-14 09:49
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HedgeTrimmer
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Great testing JJB!  

Any theory or guesses as to cause?   

Believe one person was suggesting MM's CPU was having problems processing all changes in information during sudden stop.
2-14 10:38
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jonny007
Second Officer
Germany
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Isn't a slight increase after an abrupt stop normal? The drone is tilted, the propellers turn quickly, then there is a stop and the drone is immediately level, but the speed of the propellers is not yet as low as it is during hovering. Hence the slight increase. I think every lighter drone has such a behaviour, what would be logical for me. Or am I wrong with these thoughtness ? And close to water surface better disable the vps sensors. ;-)
2-14 10:45
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JJB*
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jonny007 Posted at 2-14 10:45
Isn't a slight increase after an abrupt stop normal? The drone is tilted, the propellers turn quickly, then there is a stop and the drone is immediately level, but the speed of the propellers is not yet as low as it is during hovering. Hence the slight increase. I think every lighter drone has such a behaviour, what would be logical for me. Or am I wrong with these thoughtness ? And close to water surface better disable the vps sensors. ;-)

Hi jonny,

yes, i think this is 'normal' behaviour for a MM, having said that my MA does a better job keeping height when quick stopping like i did on the video.

My test was done with a reason ofcourse, some MM does climb and drop afterwards. Few cases on this forum dropping after quickstop but happend flying low over water.
So what is the influence of VPS height is this....

Flying out of VPS height range only the baro sensor signal is used to keep height, with accelerometer signal ofcourse.
Within VPS range...VPS do have some effect on height keeping * . But how much and what if this signal is not as steady when flying over water?

* hover your craft at 50 meters height in Sport mode, full stick down and do not release stick!
See the craft slowing down when getting into VPS height range and does stop the descend at 0.5 meter....

cheers
JJB
2-14 11:33
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JJB*
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HedgeTrimmer Posted at 2-14 10:38
Great testing JJB!  

Any theory or guesses as to cause?   

Hi HedgeTimmer,

I think that person was right, if you put more processing power in keeping the excursions less....
Guess its a summing up of different things, processing power, different drone body thus different aerodynamics, less weight (so you need to lower the upwards lift component faster than heavier drones)

And what is the effect of VPS height signal when flying over water.? see my other post in this thread.

cheers
JJB

2-14 11:39
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JJB*
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InspektorGadjet Posted at 2-14 09:49
Good tests JJB,
Now the million dollar question, what if you are out of VPS range, say 10m or higher?
All the situations where my mini did this climbs and drops was from flying within VPS range (backyard), to a lower terrain (downhill) so by the end of the travel the mini was way over VPS range...

when the storm left my country i will do some more tests, in and out VPS range, for longer period etc.

cheers
JJB

2-14 11:42
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InspektorGadjet
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JJB* Posted at 2-14 11:42
when the storm left my country i will do some more tests, in and out VPS range, for longer period etc.

cheers

Awesome JJB!
2-14 12:50
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The Saint
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it's hard to tell from your video but i get what appears to be a lot more tilt when taking off full speed ahead.  and then i get the same results as you, hardly at problems at full stop.  maybe if you get a chance you can try some of these tests with weight added instead of stock drone.  thanks for the test.
2-14 12:55
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Cal Evans
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Very cool.  Thanks for testing and sharing.

=C=
2-14 13:30
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jonny007
Second Officer
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JJB* Posted at 2-14 11:42
when the storm left my country i will do some more tests, in and out VPS range, for longer period etc.

cheers

And the ultimate test: The same procedure that you performed, but with taped VPS sensors.
2-14 13:55
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Guorium
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No need to test it over water. I tested it on Jan 16. About 2 meter abover water, mini is at my eye level so I can visually confirm deviation in altitude, I am 170cm and my foot is about 30cm above the water.
First pic shows four forward flights.
S mode
Full speed forward (headwind)
Turn around  then full speed forward (tailwind)
A total of 2 return trips.

What I observed,
Visually the drone went up after I applied full stick forward, upon release the drone slowly descend to the initial height.
I see the data agrees with my visual observation. Additionally, VPS height data is lost at high speed, which is expected.

The second pic shows 2 return trips in P mode. This time I did not turn around, just flew backward on the return legs. Everything else is the same.

I did see the same behaviors as S mode when flying forward full speed.
The backward flight made the drone descend which was then corrected by the mini upon release of the stick.

2-14 16:42
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Guorium
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The third pic, S mode at 1.7m abover a sloping grass field (downslope on outbound). Cross wind from the right this time. Same procedure as pic 2.


VPS working better now even at peak speed.

Basically, JJB visually confirms VPS is telling the truth with video and data. He experiences leveled flight before stick release and altitude deviation after stick release. I had deviation before stick release and nothing after. Completely opposite. Could it be the wind? The water? I had both. I need to do more tests on solid ground today.
Capture2.JPG
2-14 16:59
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GaryDoug
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Interesting. I did a few similar maneuvers with my 2nd new Mini a few days ago just to test it and I don't remember seeing that issue. Unfortunately it looks like I recorded no video. Maybe I can do that tomorrow.
2-14 22:07
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Lucas775
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Great test, thanks for sharing.
2-14 23:18
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jonny007
Second Officer
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Another possibility ... the reason may be that the drone is tilted and the sensors do not look down vertically but also tilted. Let's say VPS only works optimally when the drone is in a horizontal position. If it is 2 meters high, the sensors do not show 2 meters in this state, but because of the inclination, e.g. 2.30 meters. Now the drone suddenly stops, is in a horizontal position and corrects the height to just 2.30m. Anyway ... you have to be mindful of this behavior, but it's not a major problem.
2-15 02:20
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Guorium
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jonny007 Posted at 2-15 02:20
Another possibility ... the reason may be that the drone is tilted and the sensors do not look down vertically but also tilted. Let's say VPS only works optimally when the drone is in a horizontal position. If it is 2 meters high, the sensors do not show 2 meters in this state, but because of the inclination, e.g. 2.30 meters. Now the drone suddenly stops, is in a horizontal position and corrects the height to just 2.30m. Anyway ... you have to be mindful of this behavior, but it's not a major problem.

Interesting thought. We should see 2.3m in forward pitch, then less when level, then 2.3m in backward pitch during an abrupt braking. So the VPS sensor should see a dip in the altitude trace. That is not what is shown in the data though.
2-15 03:14
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DJI Stephen
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Hello and good day JJB*. Thank you for reaching out and for creating this informative video for the DJI Mavic Mini. Great work and thank you for your support.
2-15 15:53
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BigBird-2
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Interesting, Thanks.
2-15 16:54
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GaryDoug
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GaryDoug Posted at 2-14 22:07
Interesting. I did a few similar maneuvers with my 2nd new Mini a few days ago just to test it and I don't remember seeing that issue. Unfortunately it looks like I recorded no video. Maybe I can do that tomorrow.

I did my tests today and got the same results. In S mode, it rises about 6-9 inches and slowly drops after stopping. It looks to be a designed action. In P mode, it still does it but to a lesser extent and lesser even for C mode.

I did notice that the more times I repeated the test, the more error there was in the reported altitude ending with an error of about 2 feet. In other words, when ending at 5 feet above the ground, it was reported as 3 feet....etc. I did not see that on the first few tests.
2-15 19:29
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JJB*
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DJI Stephen Posted at 2-15 15:53
Hello and good day JJB*. Thank you for reaching out and for creating this informative video for the DJI Mavic Mini. Great work and thank you for your support.

Hi Stephen,

Thansk, as said i am happy with my MM. Others have some uncontolled height droppings, so hope your engineers will look into their problems.

Could you tell me the role of VPS height signal (if within range ofcourse) in relation to keeping drone at current flying height?  I think this signal is also used for height keeping in assistance to the barometric height signal, so what wil happen if the vps signal is suddenly lost ? (does the sw thinks its flying suddenly higher so a steer down command is given?)

cheers
JJB

2-16 04:06
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