Mavic does RTH without GPS signal!!!

[Alex ROV]

I am a bit confused by the way you indicate time. The flight lasted 14Min 32.8Sec. For reference are you using Ticks or something else?

I looked at the Graphs and I have seen this same pattern on my own Mavic when it is indoors. From the information I have looked at I came to the conclusion that if the IMU detects almost no movement it seems to keep the flight state in GPS mode even if the GPS signal has dropped out.

So far I have only seen this happen when the GPS drops out for very short periods and the craft has minimal movement. It might be DJI has programmed in a hysteresis effect in case the GPS lock is going in and out very fast. I think this flight demonstrates that happening.

I sampled the last bit of the Flight.

GPS Data

View attachment 13103
Movement during that period
View attachment 13104

Rob

I am also confused about his timestamp... The meaning of "32" at begining???

Your graphics are very good... I believe that between 828 and 837, when the red GPS line drops (by the end of my flight) that was the moment I crossed my window and flew indoors. At this moment RC screen changed to OPTI and Mavic became much more stable. I flew 30sec (+/-) before landing and shutdown (manually).

I believe your hysteresis theory is very right!

 

[Robbyg]

I am also confused about his timestamp... The meaning of "32" at begining???

Your graphics are very good... I believe that between 828 and 837, when the red GPS line drops (by the end of my flight) that was the moment I crossed my window and flew indoors. At this moment RC screen changed to OPTI and Mavic became much more stable. I flew 30sec (+/-) before landing and shutdown (manually).

I believe your hysteresis theory is very right!

Thanks. BTW I like this thread because your Log file is one of those few that demonstrates the way DJI programmers think. When I saw this behavior the first time I was not certain but seeing it again makes me feel a bit more confident that it is a deliberate behavior that they programmed in.

Rob

 

[msinger]

I looked at the Graphs and I have seen this same pattern on my own Mavic when it is indoors. From the information I have looked at I came to the conclusion that if the IMU detects almost no movement it seems to keep the flight state in GPS mode even if the GPS signal has dropped out.

Do you think the Mavic was really in P-GPS mode though? The flight log indicated it was not using the GPS data, so it had to really be flying in ATTI mode. No?

 

[Robbyg]

Do you think the Mavic was really in P-GPS mode though? The flight log indicated it was not using the GPS data, so it had to really be flying in ATTI mode. No?

I think it holds those last GPS coordinates and uses the IMU to recalculate it's position for a short period of time. If the movement detected by the IMU exceeds a threshold limit it knows the coordinates that it is calculating is degraded and it throws you into ATTI mode. My guess would be that they determine the movement allowed based on the accuracy specifications of the IMU module.

Rob

 

[msinger]

I think it holds those last GPS coordinates and uses the IMU to recalculate it's position for a short period of time. If the movement detected by the IMU exceeds a threshold limit it knows the coordinates that it is calculating is degraded and it throws you into ATTI mode.

Or maybe we're just interpreting the flight log incorrectly? The OP seems to be indicating he saw the mode change to ATTI in DJI GO.

 

[Alex ROV]

Or maybe we're just interpreting the flight log incorrectly? The OP seems to be indicating he saw the mode change to ATTI in DJI GO.

No... OPTI Mode when flying indoors... That's the sequence, in details:

1 - Mavic on a plataform indoors, engines OFF, RC says "OPTI MODE - READY TO GO", 5 or 6 sats on GPS indicator;
2 - Engines ON, using manual start up;
3 - RC says "TAKING OFF";
4 - Joystick UP, Mavic goes up 40cm, RC says "ATTI MODE" for less than 5s and then changes to "OPTI MODE"

 

[msinger]

Right -- that's the point I was trying to make. You're saying you saw your Mavic was in other flight modes, but your flight log indicates it was in P-GPS mode the entire time.

 

[Grey Wolf]

I never let go on sticks when indoor, I have my experience flying submarine robots over 12 years and I know we shouldn't rely on auto positioning systems... I only flight indoor moving on my way to open area or coming back to landing point, always under strong direct winds and around obstacles. It keeps switching between OPTI and ATTI but it's AMAZING how much Mavic is stable, anyway!

You fly indoors under strong and direct winds?
Please explain!

 

[Grey Wolf]

Just to be safe, when you're flying into or out of the indoor space, you should probably set your Mavic to Land or Hover in case of Signal Loss, instead of RTH.

I always set my machine to hover, even outside, in case of signal loss.

 

[scooot]

I always set my machine to hover, even outside, in case of signal loss.

For us newbies can you explain your reasoning for this.
I am keen to learn but I would of thought if you are set to hover due to signal loss and the drone is without operater knowledge hovering over a body of water would the drone just drop in the water if signal does not return and the battery runs out.

 

[Plawa]

For us newbies can you explain your reasoning for this.
I am keen to learn but I would of thought if you are set to hover due to signal loss and the drone is without operater knowledge hovering over a body of water would the drone just drop in the water if signal does not return and the battery runs out.

Question is what happens when you have LoS set to Hover but also "Smart return home" enabled.. in theory if it only has enough battery to come home it will automatically RTH... anyone care to test that?

 

[msinger]

Question is what happens when you have LoS set to Hover but also "Smart return home" enabled.. in theory if it only has enough battery to come home it will automatically RTH... anyone care to test that?

The "Smart Return-to-Home" feature only works if the Mavic is connected to the remote controller. When it disconnects, Failsafe RTH is automatically activated.

 

[adiru]

Not without a GPS signal. It would land right where it is instead.

if it had an IRU that was accurate enough in theory it could find its way back without GPS.
also why cannot it detect nearby wifi for rough location?
plus how difficult would it have been for dji to include onboard 4g?

 

[adiru]

Question is what happens when you have LoS set to Hover but also "Smart return home" enabled.. in theory if it only has enough battery to come home it will automatically RTH... anyone care to test that?

Have you tried this in the simulator?

 

[msinger]

Have you tried this in the simulator?

What exactly are you proposing be done?

 

[Plawa]

The "Smart Return-to-Home" feature only works if the Mavic is connected to the remote controller. When it disconnects, Failsafe RTH is automatically activated.

Have you actually tested that? Get the mavic maybe 100 ft away from home, turn the RC off and see what happens when it hits low battery.. but I guess in this scenario you will not be far enough to actually trigger Smart RTH before the batt goes critical.. and flying it out farther sounds like a recipe for a new "I lost my Mavic" thread.

 

[msinger]

Yes, I have personally tested all of the RTH scenarios. That's why I'm able to share my experience and knowledge with you

When you turn off the remote controller and Failsafe RTH is auto activated, the Mavic will start flying back to the home point (using the default RC signal lost setting). At that point, the Mavic will continue on its journey until it reaches the home point and auto lands. If the RC is reconnected, you can cancel RTH and take control back. If the GPS signal is lost, the Mavic will auto land at its current location. And if the battery reaches the critIcally low level, the Mavic will auto land at its current location. There are no other possible scenarios.

The Smart Return-to-Home feature cannot be initiated after another RTH is already in progress. It's impossible.

 

[Plawa]

Ok... But... Was that tested with LoS set to hover? Because you could still possibly hit a situation when it's hovering because it has lost signal and it's far enough that smart rth would kick in BEFORE any other automated landing scenario..

Not being a ****, just genuinely interested in what the behavior is..

 

[Alex ROV]

You fly indoors under strong and direct winds?
Please explain!

YES! I do... It sounds strange... And probably it is... I take off inside my apartment and find my way outside and as I live right across the beach there's always some wind blowing inside direction, causing turbulence... I have to pilot and fight against the current and turbulence for a few meters. Think about Star Wars movies when the aircrafts take off from inside the mothership and flight to outside... It's something like that...

I consider myself not that bad on joysticks after 12 years flying submarine robots, hehehe... Just the first time when I landed I had some very hard and very long seconds as I found out that Mavic goes completely WILD while she waits for the pilot to "slide to land" on screen... It looks like she disables all the autos (neither OPTI nor ATTI) and relies only on GPS (which I didn't have indoors) while that message is on screen... And to make it worse, once we "slide to land" she goes down too much softly, barely touching the ground, having no grip on surface until the engines cut off. Lesson learned: landing assistance is now OFF...

 

[Plawa]

YES! I do... It sounds strange... And probably it is... I take off inside my apartment and find my way outside and as I live right across the beach there's always some wind blowing inside direction, causing turbulence... I have to pilot and fight against the current and turbulence for a few meters. Think about Star Wars movies when the aircrafts take off from inside the mothership and flight to outside... It's something like that...

I consider myself not that bad on joysticks after 12 years flying submarine robots, hehehe... Just the first time when I landed I had some very hard and very long seconds as I found out that Mavic goes completely WILD while she waits for the pilot to "slide to land" on screen... It looks like she disables all the autos (neither OPTI nor ATTI) and relies only on GPS (which I didn't have indoors) while that message is on screen... And to make it worse, once we "slide to land" she goes down too much softly, barely touching the ground, having no grip on surface until the engines cut off. Lesson learned: landing assistance is now OFF...

Any reason to actually use slide to land? I never ever use that even under ideal conditions...