Skud75 Posted at 2016-11-26 00:37
Hello Boys,
i download the last MAVIC MANUAL and i read that the new distance for Landing inside t ...

Yes ... aircraft automatically descends and lands if RTH is triggered within 5 metres radius  of home point
Page 16

Hi DJI-Tim.

Could you say something regarding this topic and my problem with RTH?
http://forum.dji.com/forum.php?mod=viewthread&tid=74256

The instructions above keep referring to the throttle stick. Which stick is the throttle??? And yes, I've read both manuals of both the P3 S and 4k that I won and fly.

Which stick is the throttle??? In fixed wing mode 2 its the left stick. IN a drone its.....?

When flying with lots of tree cover, would it make sense to disable Smart Return to Home and set "Remote Controller Signal Lost" to hover in the advanced settings of the Main Controller Settings to keep the drone from ascending when RTH is triggered?

Thanks for the information.

guyclarkhand Posted at 2017-2-19 12:29
When flying with lots of tree cover, would it make sense to disable Smart Return to Home and set "Remote Controller Signal Lost" to hover in the advanced settings of the Main Controller Settings to keep the drone from ascending when RTH is triggered?

I would suggest you set an appropriate RTH height high enough to be well above trees. If you set it to hover when you lose signal, then it is possible that by the time you get to its last known location (it may have moved on a bit) that the battery charge will turn critical (10% by default) and it will just land in the trees or whatever is underneath it.

Aardvark Posted at 2017-2-19 13:00
I would suggest you set an appropriate RTH height high enough to be well above trees. If you set it to hover when you lose signal, then it is possible that by the time you get to its last known location (it may have moved on a bit) that the battery charge will turn critical (10% by default) and it will just land in the trees or whatever is underneath it.

Thanks for the response. I should clarify: I'm shooting beneath the tree cover, moving through a wooded area at about head-height, never letting the drone out of my sight. In that situation, it seems like the RTH function is a liability since anything that makes the drone rise without my control would lead to a collision with tree branches.

guyclarkhand Posted at 2017-2-19 13:28
Thanks for the response. I should clarify: I'm shooting beneath the tree cover, moving through a wooded area at about head-height, never letting the drone out of my sight. In that situation, it seems like the RTH function is a liability since anything that makes the drone rise without my control would lead to a collision with tree branches.

You are correct of course, hover would be the best course of action given what you've described. If you want the really tight shots you could always hold it in hand and walk through, the gimbal will do a great job in keeping the camera steady.

not sure if this has been answered in this thread ( got tired of reading all the childish bickering), . i did manage to see a real post about  negative alt in relation to homepoint and what would happen if rth was activated.  what if my rth alt is set at 30m and im flying at 30 m, will the drone rth at 30m or ascend to 60m before rth ? ( yes i rtfm, just asking for clarification)

timnwcove Posted at 2017-2-19 14:24
not sure if this has been answered in this thread ( got tired of reading all the childish bickering), . i did manage to see a real post about  negative alt in relation to homepoint and what would happen if rth was activated.  what if my rth alt is set at 30m and im flying at 30 m, will the drone rth at 30m or ascend to 60m before rth ? ( yes i rtfm, just asking for clarification)

All is in relation to the home point, so if you set RTH height at 30m and the aircraft is below that height when RTH initiated then it will rise to 30m above home point and return to home. If it were at 40m when RTH initiated then it stays at that height and returns to home, it won't drop down to 30m.
Something to be very aware of though is once RTH initiated do not operate the left stick at all, because if the aitcraft is above 20m but below its RTH height (which you set e.g 30m, 40m, 80m, whatever) then it will stop ascending to the set RTH height, and return home at whatever height above 20m the aircraft was at when left stick was operated. So if an RTH is initiated do not touch the controls until you have it in sight again.

Aardvark Posted at 2017-2-19 14:13
You are correct of course, hover would be the best course of action given what you've described. If you want the really tight shots you could always hold it in hand and walk through, the gimbal will do a great job in keeping the camera steady.

Thanks again, Aardvark.

Aardvark Posted at 2017-2-19 14:43
All is in relation to the home point, so if you set RTH height at 30m and the aircraft is below that height when RTH initiated then it will rise to 30m above home point and return to home. If it were at 40m when RTH initiated then it stays at that height and returns to home, it won't drop down to 30m.
Something to be very aware of though is once RTH initiated do not operate the left stick at all, because if the aitcraft is above 20m but below its RTH height (which you set e.g 30m, 40m, 80m, whatever) then it will stop ascending to the set RTH height, and return home at whatever height above 20m the aircraft was at when left stick was operated. So if an RTH is initiated do not touch the controls until you have it in sight again.

thanks so much for this straight forward reply.  

tim

A very Newbie. So please be patient !On my 5th flight on my phantom 3 professional.  Still in beginner mode . But can't seem to get my phantom to rth . When I press the button on either app or actual controller it just lands where ever it is.  I have set the home point but still it won't return.  I have even allowed the battery run down to the point where it should return , but still it just lands at its point at the time.I will fly again tomorrow and insure I'm 50m away from take off point , I seen a point that rth will just land if it's in 20m radius of take off . Can anyone else offer any help or settings I need to check . Thank you in advance .

Can i set home point after take off at some point a few metres away from take off point

In a hilly area will the drone maintain 20 meters above ground or run into the side of the hill.

fans56d4d7d4 Posted at 2018-6-23 03:51
In a hilly area will the drone maintain 20 meters above ground or run into the side of the hill.

Your Phantom can only maintain height at whatever level you set relative to the home point.
If you don't set an RTH height appropriate for whatever obstacles may be between where the Phantom is and the home point, you risk flying into any obstacles higher than your RTH height.

Labroides Posted at 2018-6-23 05:31
Your Phantom can only maintain height at whatever level you set relative to the home point.
If you don't set an RTH height appropriate for whatever obstacles may be between where the Phantom is and the home point, you risk flying into any obstacles higher than your RTH height.

Exactly .... your Altitude is ZERO referenced to your Take-Off point.

Therefore if you set your RTH height at 30m ... then if the ground slopes up - that slope will not be accounted for in your RTH ... if the ground or an object on it is higher than 30m than your TAKE-OFF point ... you will hit it unless you give UP stick to avoid.

Its worth looking at a topo map of your area if you live with hills / mountains ... to decide what is safe RTH.

Nigel

Will the drone maintain the preset RTH altitude up and over hills or will it fly into the side of the hill. ie. if RTM location is on the other side of a 40 meter hill will it continually climb to go over the hill keeping its 20 meters above ground as it flys or does it hit the hill half way up?

fans56d4d7d4 Posted at 2018-6-23 13:26
Will the drone maintain the preset RTH altitude up and over hills or will it fly into the side of the hill. ie. if RTM location is on the other side of a 40 meter hill will it continually climb to go over the hill keeping its 20 meters above ground as it flys or does it hit the hill half way up?

The RTH function has changed slightly over time with newer firmware.
The P4 series (and probably others) will retrace their route until control signal re-established. So if you've flown behind a hill, it will detect loss of control signal after three seconds, It should then retrace its path to re-establish communication. I have not tested this out in practice myself. If RTH Obstacle Avoidance is active then it should ascend to avoid any obstacles it encounters on the way home.

In the P4 series there is a terrain follow mode which works going uphill (max' 20 degree slope) but not downhill (you wouldn't want it to go down into a dip and lose control signal). But this intelligent flight mode is not part of the RTH procedure.

fans56d4d7d4 Posted at 2018-6-23 13:26
Will the drone maintain the preset RTH altitude up and over hills or will it fly into the side of the hill. ie. if RTM location is on the other side of a 40 meter hill will it continually climb to go over the hill keeping its 20 meters above ground as it flys or does it hit the hill half way up?

Will the drone maintain the preset RTH altitude up and over hills
No it won't.
Your Phantom has no way to know how high it is above the ground below it (unless you have a P4 and it's less than 10 metres above the ground).
Your Phantom only knows that home = zero and all heights are relative to the home point.

With regard to Obstacle Avoidance ... I thought if the obstacle is in front of the P4 .. it stops going forward ? Its only if the VPS sensors have input that it will climb over ? With VPS - that means you have to be darned close to ground ...

Not owning a P4 .. I ask.

I know that VPS on my P3P will not cause it to climb over an obstacle ... all it does is feed the height info to the FC. / give me hover/altitude hold indoors.

Nigel

Earlier the claim of auto landing at 5m was made ... actually not correct as the actual figure is :

If RTH is triggered at 20m (65ft) or less from Home Point - Auto Land will be initiated. RTH is only fully actioned at OVER 20M from Home Point.

Page 13 of P3S manual
Page 14 of P3A and P3P manuals.

The reason for this is the circle of error of GPS.

Nigel

solentlife Posted at 2018-6-24 07:13
Earlier the claim of auto landing at 5m was made ... actually not correct as the actual figure is :

If RTH is triggered at 20m (65ft) or less from Home Point - Auto Land will be initiated. RTH is only fully actioned at OVER 20M from Home Point.

The reason for this is the circle of error of GPS.
Can you explain your thinking on that?
I can't see how it makes any difference and the reason for the 20m feature is still a mystery to me.

Labroides Posted at 2018-6-24 15:34
... and the reason for the 20m feature is still a mystery to me.

My theory has always been that 20 meters is so close to the homepoint and therefore likely to be so close to the pilot that there's no point in having the AC rise to the minimum RTH height so as to safely horizontally transverse directly over the homepoint to land.  Just let it land where it is.  If there's a problem, the pilot can cancel the RTH landing in less than a second.  

Mark The Droner Posted at 2018-6-24 15:41
My theory has always been that 20 meters is so close to the homepoint and therefore likely to be so close to the pilot that there's no point in having the AC rise to the minimum RTH height so as to safely horizontally transverse directly over the homepoint to land.  Just let it land where it is.  If there's a problem, the pilot can cancel the RTH landing in less than a second.

I have an alternate theory that if you are within 20 Metres, you may be flying insde and do not want it rising up and hitting the roof.

Geebax Posted at 2018-6-24 15:49
I have an alternate theory that if you are within 20 Metres, you may be flying insde and do not want it rising up and hitting the roof.

Flying inside you often wold have trouble getting a stable GPS lock and the RTH would not work anyway, add to this that most people has flat roofs where a drone rarely have issues hitting flat on i would like to ditch that theory. Actually drones are brilliant used to get spiderwebs and dust down from the roof...

I really would like to hear a DJI engineers explanation of the reason for the 20m behavior as i can't imagine any good reason for this implementation.

Labroides Posted at 2016-11-25 06:03
Yes ... aircraft automatically descends and lands if RTH is triggered within 5 metres radius  of home point
Page 16

Page 16 of which manual please ??

P3P / P3A certainly has nothing about 5m on 16 ... but 20m on page 14.

P3S is page 13 ... again 20m.

??

Nigel

The Circle of Error is a term based on the GPS determination of probable position and its variance.

If you take a GPS plotter and leave it running for a period ... lets say some hours. You will see the plot jumps around significantly, and well outside of the claimed 2 - 3m.

My previous profession was a Professional navigator and was heavily involved in satelite navigation testing on ships ... through Transit (terrible !) and later GPS (bit of a bad name but one we all use). Been involved with Military and Commercial versions since .... as part of my Fuel assignments etc.

The Circle of Error for even the best system public can buy is 10m AVERAGE. I am fully aware that you can have handhelds and so on that give reasonably accurate position - but they are using averaging and what is termed 'jump to road' factoring. Good example of this is when your car Satnav gives you direction to turn of a highway. You choose to take other road .... the Satnav veers of onto the 'directed' road but then once it gets more than 20m (what a coincidence !) it suddenly jumps to correct road ....
The GPS you use is using various factors to reduce the error, such as in its computation of speed / direction - it will discard positions that cause large jumps.

But there is one area that the GPS is extremely poor on ... that is static or near home data. Back to my part about watching a plotter and the positional data.

I assume that DJI has decided on 20m as that is a safe distance well outside of the 10m circle. It is a factor that we as the pilot will expect to actually occur. If DJI made that circle less as say 5m or 10m ... then you really cannot g'tee action. Imagine 6m out from Home Point and RTH kicks in ... rises to RTH altitude you set (mine is 30m) then tries to land on HP !! Yeh well !!

I have to say that I am still amazed every time - the consistency of the P3 to arrive at Home Point ... but I always have in back of mind the reality of GPS ... so final landing is always under MY control.

Nigel

solentlife Posted at 2018-6-24 23:45
Page 16 of which manual please ??

P3P / P3A certainly has nothing about 5m on 16 ... but 20m on page 14.

I was replying to a query about the Mavic which automatically descends and lands if RTH is triggered when the aircraftis within a  16 ft (5 m) radius of the Home Point

solentlife Posted at 2018-6-24 23:45
Page 16 of which manual please ??

P3P / P3A certainly has nothing about 5m on 16 ... but 20m on page 14.

I think if you look at what was answered to back then it explain it all.

Labroides Posted at 2018-6-25 02:38
I was replying to a query about the Mavic which automatically descends and lands if RTH is triggered when the aircraftis within a  16 ft (5 m) radius of the Home Point

Sorry ... didn't expect a Mavic query to be in a P3A / P3P section ...

Nigel

solentlife Posted at 2018-6-25 00:09
The Circle of Error is a term based on the GPS determination of probable position and its variance.

If you take a GPS plotter and leave it running for a period ... lets say some hours. You will see the plot jumps around significantly, and well outside of the claimed 2 - 3m.

The Circle of Error is a term based on the GPS determination of probable position and its variance.
I'm well aware of what the circle of error is and understand only too well how in/accurate GPS is.
I just can't see how it makes any difference to DJI's programming of the Phantom to land in place if RTH is triggered within 20 metres.

I assume that DJI has decided on 20m as that is a safe distance well outside of the 10m circle. It is a factor that we as the pilot will expect to actually occur. If DJI made that circle less as say 5m or 10m ... then you really cannot g'tee action. Imagine 6m out from Home Point and RTH kicks in ... rises to RTH altitude you set (mine is 30m) then tries to land on HP !!
The aircraft will ascent to RTH height if slightly more than 20 metres away but land in place if slightly <20 metres away.
Whether the GPS position is accurate or +/- 10 metres, I can't see how it makes any difference.
No-one has ever come up with an explanation behind their DJI's reasoning.
V1.0 of the P3 pro manual did not have this feature but by V1.2 in July 2015, it is in the manual.
The great mystery is:  Why did DJI add this?

solentlife Posted at 2018-6-25 00:09
...If you take a GPS plotter and leave it running for a period ...  You will see the plot jumps around significantly, and well outside of the claimed 2 - 3m.

Yes - I wouldn't say it jumps around but it does move around.  This was apparent with the old Flytrex app and log.  Here's a typical screen shot from the Flytrex app which records its telemetry info twice a second.  I had placed the AC on the ground with it powered up but motors off.  The AC sat on the ground for about eight minutes.  The Flytrex system doesn't care if it's flying or not, it just records its GPS position and shows it on the map.  And it shows a track.  You can see how the AC seems to have moved around.  The homepoint doesn't move of course, but the AC appears to move.  The truth is the AC hasn't moved an inch.  It's the GPS data that changes as the seconds tick by so that its assessment of the AC's location relative to the surface of the earth changes.  At this point in the screen shot below, I hadn't even started the motors yet.  And yet it has seemingly moved up to 16 feet from homepoint and has traveled 67 feet when in fact it hasn't traveled an inch.  This is invisible on the DJI app because it's apparently programmed to not show distance from homepoint until the launch.  

KedDK Posted at 2018-6-25 02:42
I think if you look at what was answered to back then it explain it all.

Another case of people not checking what section they are posting in ...

Mavic goes in Mavic section ... Standard / SE goes in Standard section ... Pro and Adv go in Pro / Adv section etc.

I blame the daft ALL section ... people just do not look at the TAB to the left saying what section post comes from.

Plus new owners coming in can get wrong info from this sort of mix-up as people generally do not read all posts in a thread.

Nigel

solentlife Posted at 2018-6-25 03:00
Another case of people not checking what section they are posting in ...

Mavic goes in Mavic section ... Standard / SE goes in Standard section ... Pro and Adv go in Pro / Adv section etc.

Don't shoot the messenger.

I still most of all would blame the missing info in the threads, see ex. this one found among one of the first doing a simple search, beside the age could give a clue it would not be a P4P, you simply has no chance to see in witch section it was posted.
The same counts for this particular thread as OP has no avatars and the article is about DJI drones in general even the top of pages show it was posted in a Phantom section.

For sure no matter what might be done we will see this again and again, people with problems will post in the first and best thread they find sounding just a little being about the same issue or subject. Just like we often will answer something matching our preferences and experience without really reading closely and between the lines what we answer or ask about.
In this actual case it was quite easy both to expand the quote or look up the question asked when wondering the answer and it would show right away it was an answer about Mavic's RTH behavior.

Even when there would not much doubt people get asked things that are obvious, notice how often the Admins ask a user what model they have even when posting in the section that match the only avatar shown at the profile, that's just the way we are.
Always look on the bright side of life, now you have helped making it even more obvious for newbees that this answer was specific for the Mavic, of course, provided they read the following posts.

The landing out within 20m makes sense to me - but I've been working / using GPS all my life since its first days after Transit....

I think the problem for most is that they assume great accuracy as that is what they appear to see with the later multi-channel units. But they also fail to understand that a 32ch GPS unit does not use 32 sats to calculate position. It will select the best and discard rest ... as it in fact only uses a set less number ... some use 8 ... some use 12 .. some use more ... but never all. A GPS gives 2D position info with 3 sats ... but needs 4 sats or more for 3D. Next is that a GPS only provides position info at an instant. That is then compared to previous position to derive speed and direction of movement. The calculation being a Great Circle ... but now I am dropping into my formal career world.
A good sat unit such as professional nav gear has user settable averaging and position data timing. this is to assist with programming out errors as you get further N / S in latitude for example. Most users though leave as default as this is good enough to make arrival at desired location.

Nigel

solentlife Posted at 2018-6-25 10:12
The landing out within 20m makes sense to me - but I've been working / using GPS all my life since its first days after Transit....

I think the problem for most is that they assume great accuracy as that is what they appear to see with the later multi-channel units. But they also fail to understand that a 32ch GPS unit does not use 32 sats to calculate position. It will select the best and discard rest ... as it in fact only uses a set less number ... some use 8 ... some use 12 .. some use more ... but never all. A GPS gives 2D position info with 3 sats ... but needs 4 sats or more for 3D. Next is that a GPS only provides position info at an instant. That is then compared to previous position to derive speed and direction of movement. The calculation being a Great Circle ... but now I am dropping into my formal career world.

Is GPS kind of inaccurate or is it because the US who run the GPS system are adding a factor that gives GPS receivers a deviating reading?
That's what I heard - the US military itself can pinpoint with GPS pretty exact since they know the deviation factor (which changes constantly)

There is an airport in the Swiss mountains, I think it's Sion. It's right behind a mountain range and hard for landings, esp. at night. And planes can land there using GPS.
They have a GPS receiver near the landing strip and obviously know it's position 100% accurately.

Then the system checks  which position for that receiver is given by GPS which is not as accurate.
That deviation factor is forwarded to a landing plane and the planes GPS reading is corrected accordingly.
That's an automated process of course. Planes can land within an accuracy of inches.

And now let's transfer all this to the Phantom :-)

Labroides Posted at 2018-6-25 02:56
The Circle of Error is a term based on the GPS determination of probable position and its variance.
I'm well aware of what the circle of error is and understand only too well how in/accurate GPS is.
I just can't see how it makes any difference to DJI's programming of the Phantom to land in place if RTH is triggered within 20 metres.

"The great mystery is:  Why did DJI add this?"

It may not be a mystery after all. I contacted DJI support Facebook/USA with that question.
(And another one beforehand. They come back within a couple of minutes with detailed explanations. Nice!)

Here is their answer:  

For your concern, the drone was programmed that way. RTH function is a safety feature that you can trigger if the drone needs to return to the home-point depending on the circumstances and the location. If the drone is near, then RTH is not needed, since you can use the RC to move the drone to a safer place, or to the home point.

To me it's an easy answer that makes sense. Why would you need the RTH function with ascending first (and maybe ending up in trees)  if the drone is so close while still being able to interrupt that 'Landing Here' procedure to maneuver the drone to a safe place?

  

Eric13 Posted at 2018-6-25 12:05
Is GPS kind of inaccurate or is it because the US who run the GPS system are adding a factor that gives GPS receivers a deviating reading?
That's what I heard - the US military itself can pinpoint with GPS pretty exact since they know the deviation factor (which changes constantly)

Is GPS kind of inaccurate or is it because the US who run the GPS system are adding a factor that gives GPS receivers a deviating reading?
That's what I heard - the US military itself can pinpoint with GPS pretty exact since they know the deviation factor (which changes constantly)
What you are describing was known as Selective Accuracy.
The US removed SA back in May 2000 and since then publicly available GPS is as accurate as military GPS.

Consumer GPS doesn't have pinpoint accuracy.
You need expensive survey grade GPS to get that.