A more complex kind of question.

[MavicKhan]

Something is bugging me, as I do not quite understand it and find it crucial to fully get how the Mavic works in order to be a competent and safe operator.

The iPad Mini 2 i bought 2nd hand specifically to work with the Mavic does not have GPS.

If I fire it up in the field and connect it to the controller, the map section of the DJI Go 4 app shows blank.

Makes sense, since there is no GPS nor wi-fi for the iPad Mini to connect to.

If I then start my Android Tab, which features 3G/4G, activate the wi-fi hotspot functionality and connect the Ipad Mini wi-fi to this ad-hoc generated hotspot, the DJI Go 4app on the iPad loads the map.

This makes sense, because the DJI Go 4 app is fetching the map info over the wi-fi connection and then, in turn, over the 3G/4G connection established by the Android Tab.

When I then fire up the Mavic, it goes through it’s initialization little dance and the app reports “the home point has been set” and shows the “H” on the map.

This also makes sense. The Mavic is getting a GPS position and it’s transmitting it via the controller to the app which marks it accurately, function of the correctly displayed map.

The app then keeps showing the correct position and orientation of the device throughout the flight, because it is receiving that information from the controller which, in turn, receives it from the Mavic via the radio link.

Now, on one of my very first flights, after reading the manual and duly instructed by all the information I could get here and in other good resource sites during the time I was waiting for my unit, I went to a site I knew would be a bit windy and pretty contaminated with radio-electric interference, function of the multiple cell towers installed in the place.

I made several careful test at very low height, evaluating the correctness of the “magnetic interference” messages, saw the unit changing from “P” to “ATTI” for brief moments on account of said interference, ventured to gain a bit of additional height and, surely enough, saw the drone drifting with the wind while on “ATTI”, me having to go into “Sport” mode to fly it back after it had drifted a couple hundred yards away.

(..Heart pounding all the way, for sure, but it had to be done so I could get confidence in the whole system...)

Now, what I don’t understand is:

If the Mavic entered “ATTI” mode and drifted away, it means it no longer had a valid GPS position but, yet, the app was still correctly showing the UAV position on the map throughout the entire flight.

If the Mavic lost GPS, it could not calculate its own position and relay it back to the app, via the controller.

Also, if the iPad Mini does not have GPS, it cannot conversely convey to the Mavic some sort of home positioning so the UAV can compute bearing and distance from that “enriched telemetry” (...something that would be far-fetched, anyway).

If this is all true, how can the app then keep displaying an accurate Mavic position while it is in “ATTI”?

If that was only a brief fluke due to the fact that the GPS signal might have been coming in and out warranting position calculation but not “P” mode engagement, am I correct to assume that, if a “real” (as in lengthy) GPS loss with a durable reversion to ATTI, coupled with a “loss of communication with the controller” occurs and the craft isn't able to perform the Fail Safe RTH (as outlined in the manual) its position and heading won’t be valid ones, on the map, making it impossible to recover the craft BVLOS?

Thank you for any inputs.

MK

 

[Mattman]

TL;DR

 

[Mako79]

Lets ignore how your ipad is getting map data. Its just an overlay of roads/streets/grass etc.

How many sats is showing on your sat count?
If >7 then the Mavic will be logging and sending location data back to the mavic continuously provided you are still receiving 2.4ghz,
There is a high possibility that your mavic is switching to ATTI because due to erroneous compass data. You can tell if this happening by the GPS counts. If your sat counts is like 14 and the mavic is switching to ATTI then highly likely you have done a bad compass calibration at a location full of magnetic influence.

I would suggest going to an open grassy field and doing a clean compass calibration, once and once only. The only other time i would do one is if there is a software update or if i have traveled 70km east/west.

 

[F6Rider]

The Mavic was drifting with the wind because in ATTI is is still getting GPS data, it is just not using it to hold position when you release the sticks. So you are in manual flight mode with the Mavic only holding altitude, but not position. And unless the wind speed was close to 20 MPH there was no need to switch to sport mode, unless you did it just to get back faster. I so wish DJI had not taken our ability to switch to ATTI when we wanted to, as every pilot needs to learn to fly in manual, although to be fair it's not full manual as it will hold altitude well.

 

[MavicKhan]

Lets ignore how your ipad is getting map data. Its just an overlay of roads/streets/grass etc.

How many sats is showing on your sat count?
If >7 then the Mavic will be logging and sending location data back to the mavic continuously provided you are still receiving 2.4ghz,
There is a high possibility that your mavic is switching to ATTI because due to erroneous compass data. You can tell if this happening by the GPS counts. If your sat counts is like 14 and the mavic is switching to ATTI then highly likely you have done a bad compass calibration at a location full of magnetic influence.

I would suggest going to an open grassy field and doing a clean compass calibration, once and once only. The only other time i would do one is if there is a software update or if i have traveled 70km east/west.

Thank you for your input but the answer is not quite what I was looking for.

My Mavic operates flawlessly (...until now, at least). My question was a conceptual/design one, about how things were designed to operate.

MK

 

[MavicKhan]

The Mavic was drifting with the wind because in ATTI is is still getting GPS data, it is just not using it to hold position when you release the sticks. So you are in manual flight mode with the Mavic only holding altitude, but not position. And unless the wind speed was close to 20 MPH there was no need to switch to sport mode, unless you did it just to get back faster. I so wish DJI had not taken our ability to switch to ATTI when we wanted to, as every pilot needs to learn to fly in manual, although to be fair it's not full manual as it will hold altitude well.

Thank you. Just what I was trying to get at.

So, we still get correct position and heading info on the map in ATTI because it still receives GPS info?

This begs a question, though:

If GPS calculated position is accurate enough to still send it to the controller, why does the craft switch to ATTI?

You wished another functionality would be available, I only wish things could be clearer in the manual for those that already exist.

If you do a search, "ATTI" appears only 3 times in the manual.

In the first two, as sideways notes to another function:

(1) Under Tripod Mode: "Only use Tripod Mode where the GPS signal is strong or light conditions are ideal for the vision system. If GPS signal is lost and if the vision system cannot function, it will automatically switch to Atti mode."

(2) Under Forward and Downward Vision system: "The aircraft will switch from P-mode to Atti mode automatically if neither the GPS nor the Forward and Downward Vision system are available."

The last entry only serves to makes things even more confusing as, under "Remote Controller LCD Screen Menu Information", "Remote Controller Status", the "ATTI MODE" label is listed as denoting "In P-ATTI" mode.

One reads it and, if it was not for outside information, for sites like this one, one would wonder, what does the "P" stand for in "P-ATTI"?. What does it actually do?

I feel that if a manufacturer is going to produce and sell flying devices, devices that fall under aeronautical jurisdiction, it better hire some more competent manual writers or they are opening themselves to all kinds of liability.

MK

 

[F6Rider]

Thank you. Just what I was trying to get at.

So, we still get correct position and heading info on the map in ATTI because it still receives GPS info?

This begs a question, though:

If GPS calculated position is accurate enough to still send it to the controller, why does the craft switch to ATTI?

You wished another functionality would be available, I only wish things could be clearer in the manual for those that already exist.

If you do a search, "ATTI" appears only 3 times in the manual.

In the first two, as sideways notes to another function:

(1) Under Tripod Mode: "Only use Tripod Mode where the GPS signal is strong or light conditions are ideal for the vision system. If GPS signal is lost and if the vision system cannot function, it will automatically switch to Atti mode."

(2) Under Forward and Downward Vision system: "The aircraft will switch from P-mode to Atti mode automatically if neither the GPS nor the Forward and Downward Vision system are available."

The last entry only serves to makes things even more confusing as, under "Remote Controller LCD Screen Menu Information", "Remote Controller Status", the "ATTI MODE" label is listed as denoting "In P-ATTI" mode.

One reads it and, if it was not for outside information, for sites like this one, one would wonder, what does the "P" stand for in "P-ATTI"?. What does it actually do?

I feel that if a manufacturer is going to produce and sell flying devices, devices that fall under aeronautical jurisdiction, it better hire some more competent manual writers or they are opening themselves to all kinds of liability.

MK

If it says that you are in P-ATTI mode, your aircraft will not stabilize the horizontal position but only the vertical one with the barometer above ground sensor range. This is due to a weak GPS signal and/or interference affecting the compass in most cases. Some pilots have stated that they get this mode while still having plenty, >6 satellites locked in, this has not happened to me but might be a software glitch.

 

[f3honda4me]

If there is magnetic interference such that causes a compass issue it will go into ATTI even with full gps. P mode requires gps AND compass. If compass is not working due to an issue all the GPS satellites in the world won't stop the craft from going into ATTI.

 

[MavicKhan]

If there is magnetic interference such that causes a compass issue it will go into ATTI even with full gps. P mode requires gps AND compass. If compass is not working due to an issue all the GPS satellites in the world won't stop the craft from going into ATTI.

I understand that...even from old reports here...that is why I wanted to test things out, back in mid December.

What I don't understand is: If the magnetic interference is enough to compromise "P" mode, how come position and heading references are still being transmitted to the tab, via the controller?

MK

 

[f3honda4me]

I understand that...even from old reports here...that is why I wanted to test things out, back in mid December.

What I don't understand is: If the magnetic interference is enough to compromise "P" mode, how come position and heading references are still being transmitted to the tab, via the controller?

MK

Position would still be transmitted. That's GPS. Heading would be compass. In ATTI mode it doesn't mean the drone necessarily can't tell where it is pointed. It's still going to tell you what it thinks its heading is. It simply isn't able to tell if it's correct, hence ATTI mode.

In other words this is normal.

 

[kiteboy]

I understand that...even from old reports here...that is why I wanted to test things out, back in mid December.

What I don't understand is: If the magnetic interference is enough to compromise "P" mode, how come position and heading references are still being transmitted to the tab, via the controller?

MK

Hi,

It switches to Atti when the data being received is not accurate enough to ensure safe autonomous flying (just holding vertical and horizontal position is still autonomous) this doesn't mean it isn't getting any info it is just that a certain threshold have been programed in the firmware and it decides that it is safer to switch to atti and let the pilot knows it have to control the drone himself

That's why it is still able to show position and bearing!

This is not like the usual car or mobile phone gps this is making millions of operations by the second just to hover in place and not drift.

I while back I helped a friend to build an 450 from DJI and you could se the output (verbose) of what the drone what's actually doing just sitting on a table powered on and it was so fast that you just couldn't read anything! (I remember that the GPS feed had 6 or 7 decimal positions) And that one had only gps and regular sensors! Imaging that adding the VPS, obstacle avoidance, HD feed, sonar, etc!

 

[MavicKhan]

F3honda4me and Kiteboy, great input, thanks.

So, when under "Failsafe RTH" the manual issues the warning "Aircraft cannot return to the Home Point when the GPS signal is weak (displays grey) or unavailable", we might still be able to manually recover it, if the GPS and Compass is still not compromised enough and the position and heading are still displayed in the app, correct?

MK

 

[kiteboy]

I think you could! But with the redundancy embedded in the mavic it would be an extreme situation, it might exit autonomous flight modes but I think RTH would work even, it would be a risky but interesting test!

I always try to be aware the heading and approximated position when flying! And try to look at the screen to look for terrain remarks that allow me to have a little bit of confidence in case something go wrong

 

[f3honda4me]

If you are in ATTI mode for one reason or another, return to home will NOT work. I've seen many "fly always" from people who did this only to watch their drone disappear because they don't understand this important fact.

 

[Andrew F]

Position would still be transmitted. That's GPS. Heading would be compass. In ATTI mode it doesn't mean the drone necessarily can't tell where it is pointed. It's still going to tell you what it thinks its heading is. It simply isn't able to tell if it's correct, hence ATTI mode.

In other words this is normal.

Yes. It has enough GPS to sort of know its location, but the software has determined a lower confidence level such that it switches to the ATTI mode. More control over this would be nice (like a user set confidence level) and 100% agree a manual ATTI mode is really a must have.

 

[MavicKhan]

If you are in ATTI mode for one reason or another, return to home will NOT work. I've seen many "fly always" from people who did this only to watch their drone disappear because they don't understand this important fact.

Yes, that is well established.

MK

 

[erkme73]

Regardless of what causes the compass to deviate from the GPS data, when it happens the flight controller will take the compass data as gospel and will ignore the GPS data. When that happens, the GPS indicator will go from full strength (showing numerous satellites with all white bars populated) to a single red bar... Though the number of satellites may not change at all. Then you'll get the warning that GPS signal is weak, followed by the automatic switch to atti mode.

The reality is that the GPS signal is still 100% and you haven't lost it at all (as evidenced by the location positioning on the map). It's just that the flight controller has aborted the idea of using the GPS data for position hold due to the discrepancy with the compass data.

All that said, the real question is, what is causing the sudden compass data error that makes the MP abort using the GPS? That can be a number of things, including legitimate magnetic interference, poor compass calibration, or hardware failure.

If you find the you can cause the switch to atti or strong magnetic interference warning to occur under specific conditions with some regularity, I would proffer that you have a hardware issue.

I (and many others here) have had a documented issue where high rpm and motor load would cause the rear compass to experience enough noise that it would cause the flight controller to switch to atti mode. And, while DJI did issue a firmware update that would force the flight controller to switch to the less-noisy front compass, those with this issue could get their unit repaired or replaced under warranty. Having done so myself, I have not had any more strong magnetic interference warnings, and not a single atti switch over since the repair.

It is important to understand that when the GPS and compass data deviate, it takes some time (maybe 30 seconds) before the FC officially kicks the GPS data to the curb, and switches to atti mode. Until that happens the controls and hover stability may get wonky. Once in atti mode, however, you should be able to control the MP as normal - it just won't stay put.

Where I think some people have problems beyond controlling in atti mode is when the unit is switching repeatedly back and forth between GPS and atti. It's during that FC negotiation over which mode to be in that flight controls may not work as expected.

When that happens at a distance beyond VLOS, or when they sky has gotten too dark to get proper visual orientation, panic can set in and aircraft loss ensues.

 

[erkme73]

TL;DR

Crazy helpful post.

 

[Andrew F]

Regardless of what causes the compass to deviate from the GPS data, when it happens the flight controller will take the compass data as gospel and will ignore the GPS data. When that happens, the GPS indicator will go from full strength (showing numerous satellites with all white bars populated) to a single red bar... Though the number of satellites may not change at all. Then you'll get the warning that GPS signal is weak, followed by the automatic switch to atti mode.

The reality is that the GPS signal is still 100% and you haven't lost it at all (as evidenced by the location positioning on the map). It's just that the flight controller has aborted the idea of using the GPS data for position hold due to the discrepancy with the compass data.

All that said, the real question is, what is causing the sudden compass data error that makes the MP abort using the GPS? That can be a number of things, including legitimate magnetic interference, poor compass calibration, or hardware failure.

If you find the you can cause the switch to atti or strong magnetic interference warning to occur under specific conditions with some regularity, I would proffer that you have a hardware issue.

I (and many others here) have had a documented issue where high rpm and motor load would cause the rear compass to experience enough noise that it would cause the flight controller to switch to atti mode. And, while DJI did issue a firmware update that would force the flight controller to switch to the less-noisy front compass, those with this issue could get their unit repaired or replaced under warranty. Having done so myself, I have not had any more strong magnetic interference warnings, and not a single atti switch over since the repair.

It is important to understand that when the GPS and compass data deviate, it takes some time (maybe 30 seconds) before the FC officially kicks the GPS data to the curb, and switches to atti mode. Until that happens the controls and hover stability may get wonky. Once in atti mode, however, you should be able to control the MP as normal - it just won't stay put.

Where I think some people have problems beyond controlling in atti mode is when the unit is switching repeatedly back and forth between GPS and atti. It's during that FC negotiation over which mode to be in that flight controls may not work as expected.

When that happens at a distance beyond VLOS, or when they sky has gotten too dark to get proper visual orientation, panic can set in and aircraft loss ensues.

Which shows the importance of having RTH landmarks established so you can safely get your drone back. Prepare for the worst, enjoy the best.

 

[zimode]

If your in ATTI mode, will the Map view show which direction the Mavic is pointed.. as It would be hard to try to figure out from a distance if it's flying towards you or away from you.. ( I have a hard time seeing it when it's way out there.. and if I glance down to the controller some time I lose sight of it in the sky and frantically scan to see it..)