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RTH Inaccuracy...
1646 30 2016-12-29
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ocelot27
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Hello all,

So i've seen all the videos of Mavics precisely landing on exactly the same spot from where they took off if there is a good visual cue on the landing spot.  This has not been the case for me - I have chalked an asymetric white on black cross on my landing spot (driveway) about 3 x 4 feet and have all the settings (or at least I think I do) set correctly for the visual sensors to do their thing.  I have very good GPS signal but my RTH landings have been on average 5-10 feet off.  In one case I had to take control because the caft was going to descend on my garage building.  What gives???

-john
2016-12-29
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jetek
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Have you tried to calibrate the compass before take off?
2016-12-29
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ocelot27
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jetek Posted at 2016-12-29 11:52
Have you tried to calibrate the compass before take off?

Yes - also have an Inspire 1 Pro so I am familiar with the app etc - just not a regular on the forum... the inspire is much more accurate...
2016-12-29
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ocelot27
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jetek Posted at 2016-12-29 11:52
Have you tried to calibrate the compass before take off?

I should add, though I think it's irrelevant, I occasionally get an RF interference warning from the wifi in and around my house - this should not affect the VPS, GPS etc - only the controller link.  And, unfortunately, I haven't been out and about with the Mavic yet because I want to nail down it's flight characteristics/bugs before i go live with it.
2016-12-29
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Jake Phantom 3
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When you take off do you hover above your landing spot (about 10ft) for a bit so the Mavic can get a visual of what to come back to? If not, this should fix it.
2016-12-29
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ocelot27
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Jake Phantom 3  Posted at 2016-12-29 13:58
When you take off do you hover above your landing spot (about 10ft) for a bit so the Mavic can get a visual of what to come back to? If not, this should fix it.

I've been hovering a little lower (4-5 ft) then ascending with no stops right above the cross marker, flying around then testing the RTH - params set at 50m to clear trees...  What I don't get is that the GPS alone sholud get it closer than it has been - my Inspire lands within a foot of it's TOP.  I wish the software confirmed that VPS has recognized and stored the take off point much the way it confirms the home point - which really are one and the same.  Does anyone know how the VPS records this info - i.e. at what altitude, how long after lift off etc etc...
2016-12-29
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Jake Phantom 3
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Yea, GPS might have to do with it. I've had my P3S land within inches, and several feet away, depends on how many satellite's at take off I guess.
2016-12-29
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DJI-Ken
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Are you following the requirements for Precision Landing stated in the manual?
Screen Shot 2016-12-29 at 4.16.42 PM.png
2016-12-29
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ocelot27
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DJI-Ken Posted at 2016-12-29 15:18
Are you following the requirements for Precision Landing stated in the manual?

OK - I'm going to do one final test - take off from the cross marker, confirm HP after TO, ascend to 50m and activate the RTH - that should put the drone back on the cross marker, correct?

-john
2016-12-30
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Mullheliflier
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I have tried this with a 16" drone pad. The first time it landed exactly and I mean exactly where it took off from. Subsequent landings have always landed on the pad within six inches. When it comes down it will be out a bit then goes into precision landing mode and moves over and onto the pad. Amazing!
2016-12-30
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gnom
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How long and at what height do i have to hover over the homepoint to let the mavic take the pictures to land safely again after RTH? There are no messages from the app about that.


2016-12-30
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DJI-Ken
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ocelot27 Posted at 2016-12-30 09:46
OK - I'm going to do one final test - take off from the cross marker, confirm HP after TO, ascend to 50m and activate the RTH - that should put the drone back on the cross marker, correct?

-john

It needs to confirm Home Point before takeoff, not after.
2016-12-30
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DJI-Ken
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Mullheliflier Posted at 2016-12-30 11:57
I have tried this with a 16" drone pad. The first time it landed exactly and I mean exactly where it took off from. Subsequent landings have always landed on the pad within six inches. When it comes down it will be out a bit then goes into precision landing mode and moves over and onto the pad. Amazing!

It does work great when it's set up properly and following the guidelines.
2016-12-30
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DJI-Ken
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gnom Posted at 2016-12-30 13:51
How long and at what height do i have to hover over the homepoint to let the mavic take the pictures to land safely again after RTH? There are no messages from the app about that.

The directions I posted above says ascend to at least 10m.
Wait until it locks the home point, then take off and only use the throttle and slowly ascend to 10m and if the ground is within the guidelines, it will do the precision landing.
2016-12-30
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Andrewmg08
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I personally have noticed a decrease in RTH precision after the latest firmware update!
2016-12-30
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Logger
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That's the secret.  If you want it to precision land always, climb vertically at least 10m (30') without rotating or doing anything else with the controls. The landing pads and so on are nice to have but IMO the initial vertical ascent to >10m is essential for it to work.  I have found it to work well and out the Mavic within a foot or  less of launch point. I also tend to do this initial climb when it builds its image library at less than full climb rate to give it a chance to capture whatever the required number of images are.  So this precludes the Apocolypse Now low level flashy departure move but gains a precision landing as a trade off.
2016-12-30
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Airwater
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ok but it is supposed to land within centimeters not feet from the takeoff point.
2016-12-30
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Logger
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Airwater Posted at 2016-12-30 17:47
ok but it is supposed to land within centimeters not feet from the takeoff point.

...and that is exactly what mine does.
2016-12-30
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DRONE-flies-YOU
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Andrewmg08 Posted at 2016-12-30 14:36
I personally have noticed a decrease in RTH precision after the latest firmware update!

Yep, possibly.  My Mavic thinks a truck looks the same as a patterned concrete walkway 5 feet away - THIS when I'm 100% testing the precision landing the other day.  
2016-12-30
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DJI-Ken
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Logger Posted at 2016-12-30 17:12
That's the secret.  If you want it to precision land always, climb vertically at least 10m (30') without rotating or doing anything else with the controls. The landing pads and so on are nice to have but IMO the initial vertical ascent to >10m is essential for it to work.  I have found it to work well and out the Mavic within a foot or  less of launch point. I also tend to do this initial climb when it builds its image library at less than full climb rate to give it a chance to capture whatever the required number of images are.  So this precludes the Apocolypse Now low level flashy departure move but gains a precision landing as a trade off.

That's correct, the manual says you must ascend straight up to at 10m.
2016-12-30
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DJI-Ken
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Airwater Posted at 2016-12-30 17:47
ok but it is supposed to land within centimeters not feet from the takeoff point.

Yes, when properly done.
2016-12-30
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colonel00
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So what is "acceptable" in regular RTH?  I haven't played with the precision RTH and honestly don't know that I'd use it that much.  However, for everyday usage, I'd think the Mavic should be able to land within a meter of the takeoff point or so.  Is this a fair expectation?

Recently home for Christmas, I took off from my driveway with at least two meters clear in every direction but when trying to show my father how RTH worked, I had to guide it back as it landed as it was well outside of that area.  I know GPS positioning isn't always pinpoint but what should be considered acceptable?
2016-12-30
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Heavysledz
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So how much does the GPS fix have to do with this because today I did just what the instructions posted above by DJI-Ken and when I performed a RTH it was about 12 feet off. I waited for the RC to audibly tell me it has stored the home position and then I took off vertically but didn't go the recommended 30 feet and the proceeded to fly around. I feel it was off because when I first took off, i only had 9 satellites and when I landed I had 13. So the stored coordinates for the home position likely changed based on the stronger GPS signal at landing vs takeoff. It is like when you are on Google maps and just sitting still and you see you position drifting around as the GPS signal gets weaker or stronger......Here is a picture of my GPS data fro the flight i am referencing:

GPS Flight Data

GPS Flight Data
2016-12-31
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bigcheese
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you have to initiate rrh outside of a small circle around the homepoint, as described in the manual... some meteres... because if you are inside it will just descend where it is ;) so fly away 50m an then initiate rth... does it tell you in the app about precission landing ?
for me this works perfectly...
2016-12-31
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bigcheese
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ok something like localisating landing spot... and make sure you have no faulty stick inputs in the replay, perhaps some glitch with the controller?
IMG_8488.PNG
2016-12-31
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Anthony566
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My RTH retuns within a few inches of the take off position and Always on my landing pad.
2016-12-31
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Heavysledz
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bigcheese Posted at 2016-12-31 04:53
you have to initiate rrh outside of a small circle around the homepoint, as described in the manual... some meteres... because if you are inside it will just descend where it is ;) so fly away 50m an then initiate rth... does it tell you in the app about precission landing ?
for me this works perfectly...

I think your right....I initiated it when I was pretty much directly overhead. I need to initiate it when I am further away and see how it does....
2016-12-31
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ocelot27
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DJI-Ken Posted at 2016-12-30 14:04
It needs to confirm Home Point before takeoff, not after.

yes - understood - I misspoke -- so it seems I'm not the only one experiencing RTH inaccuracy - whether it be VPS enabled or GPS enabled - my Inspire is never more then 0.5m away from the exact TOP -- my Mavic has needed aborts and corrections to get it to not descend on various obsticles around my testing area.  The point is, if you correctly input the RTH altitude to not hit tree tops etc then the drone should be able to land (with VPS OR GPS )in an area 5m^2 - is that not correct? - I just want someone to spell out what the expected acceptible error within both the VPS and GPS systems with regard to RTH.  I fly in woodland a lot and descending down in a clearing is often how I land - I won't use the RTH function if I can't rely on it to meet whatever criteria my landing spot has in terms of uobstructed verticle airpace.
2016-12-31
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ocelot27
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ocelot27 Posted at 2016-12-31 12:51
yes - understood - I misspoke -- so it seems I'm not the only one experiencing RTH inaccuracy - whether it be VPS enabled or GPS enabled - my Inspire is never more then 0.5m away from the exact TOP -- my Mavic has needed aborts and corrections to get it to not descend on various obsticles around my testing area.  The point is, if you correctly input the RTH altitude to not hit tree tops etc then the drone should be able to land (with VPS OR GPS )in an area 5m^2 - is that not correct? - I just want someone to spell out what the expected acceptible error within both the VPS and GPS systems with regard to RTH.  I fly in woodland a lot and descending down in a clearing is often how I land - I won't use the RTH function if I can't rely on it to meet whatever criteria my landing spot has in terms of uobstructed verticle airpace.

OK - did a bunch of tests with a slightly bigger marker on the landing spot (about 1 x 1.5m) and a slow initial ascent to 10m with no other inputs seems to be reliable - but I also recalibrated the IMU outside at ambient temp... I'm getting +/- 0.1-0.2m accuracy now at worst and spot on at best.
2017-1-1
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Logger
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Good the hear it is working for you now. Your level of accuracy it about what I see, when precision landing gets used. Preciosn Landing in Green pops up as it starts its final descent followed by "Precision Landing refining aircraft position" as it slews the mavic back over the target. I doubt your IMU recal effected it much. Never touched my IMU in the past 250 flights and Precision landing does a fine job when it works.  With Precision Landing turned Off I see about ~ +/-3.0m accuracy.  
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DJI-Ken
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ocelot27 Posted at 2017-1-1 13:25
OK - did a bunch of tests with a slightly bigger marker on the landing spot (about 1 x 1.5m) and a slow initial ascent to 10m with no other inputs seems to be reliable - but I also recalibrated the IMU outside at ambient temp... I'm getting +/- 0.1-0.2m accuracy now at worst and spot on at best.

That's correct, you want no stick input while ascending to 10m. And the slow ascent helps.Glad you getting closer landings now.
2017-1-2
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