Opti mode, balcony launch, unexpected behavior

[borislip]

I've just launched my Mavic from the balcony, without establishing a good GPS signal first, thinking "it will get the GPS when its out, also establishing a safer RTH point this way".

The moment the Mavic was up in the air (hand launch), in opti mode, the remote started to warn me about max alt, the bird slowly descending to a very low altitude above the ground, and no joysticks input would cancel the descent. Luckily, i couls steer it away from the nearby bushes. About 10 seconds later it got GPS fix, the warning has dissapeared, and the bird flew as expected, allowing me to raise it up.

What in the world has just happened??! What "max alt"??! I am not in a beginner mode, my max alt is set at 120m (and without the GPS it shouldn't even know how high it is). Why did it behave this way? Did it just try to descent to the visual sensors range, no matter what??!

This kind of unexpected strange behavior is starting to undermine my trust in this machine. It starts to feel overcompicated, with no way to regain manual control in an emergency, and sooner or later it is going to end badly.

 

[gregw]

This is the way that DJI has decided to deal with "unauthorised" flight... e.g. when the Mavic doesn't know it's GPS co-ordinates and you are flying via OPTI, maximum altitude is 5M/16 feet. If you turn of VPS, then maximum altitude is 30M/98 feet. This was already demonstrated by an old Mavic video by someone who flew it off his balcony and the same thing occurred...

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The official DJI reply back then was that this issue is because the Mavic this guy had is a prototype and this won't happen with production Mavics... Official DJI Mavic ***Owner and Developer'sThread*** - Page 128 - RC Groups, but obviously, that's not true...

 

[Falcon1az]

Yikes.
It doesn't sound right. Very good reason to be very deliberate, thorough, and cautious when preparing (checklist), during, and after flight.
It wasn't in Sport-mode vice P-mode? Not that this would explain an altitude warning.
Current firmware?

 

[Marco Cantieni]

I can confirm that the max altitude in. VPS mode is approx. 5 meters related from your starting point. As soon you leave your balconies ground the VPS detects the new height it tries to adapt. This surprise can make your adrenalin flowing. This is a behavior DJI should explain in the manual.

Taking of from a balcony is also risky because you are mostly likely near to big metal structures and probably get a lot of interference from Wifis.

 

[borislip]

Yes, current FW. With VPS enabled. And this is absolutely ridiculous. Hope someone is going to find a way to hack this stuff. I've read somewhere the Mavic got a secret USB command to enable and ADB root shell, maybe finding that command would be a good place to start. AFK now, can't really do any Googling.

:-(

 

[borislip]

I can confirm that the max altitude in. VPS mode is approx. 5 meters related from your starting point. As soon you leave your balconies ground the VPS detects the new height it tries to adapt. This surprise can make your adrenalin flowing. This is a behavior DJI should explain in the manual.

Taking of from a balcony is also risky because you are mostly likely near to big metal structures and probably get a lot of interference from Wifis.

This wasn't 5m from the starting point. It weny about 5m agl, a good 10m below the launch point!

 

[Zoso]

I am curious why you decided to launch off a balcony situated with a massive amount of steel and undoubtably wifi interference ? Was it for testing reasons ?

 

[its2loud]

I am curious why you decided to launch off a balcony situated with a massive amount of steel and undoubtably wifi interference ? Was it for testing reasons ?

Yes. Same here. And also why you though it would be best (safest) to establish GPS signal once in flight. Seems like the Mavic behaved exactly as it was programmed to do considering the information it had.

 

[borislip]

I am curious why you decided to launch off a balcony situated with a massive amount of steel and undoubtably wifi interference ? Was it for testing reasons ?

Ive testes the communication before, by leaving the Mavic on that balcony and walking away with the remote. I've been fine up to 1km away, on the ground, with the Mavic at the balcony. So i've assumed as long as i can confidently hand launch, there is no danger in doing so.

 

[borislip]

Yes. Same here. And also why you though it would be best (safest) to establish GPS signal once in flight. Seems like the Mavic behaved exactly as it was programmed to do considering the information it had.

Because mid-flight it would record the RTH point at the location it got the GPS fix, while otherwise it would record the handheld position near the balcony, the worst place to try to autoland on. Sure, i could set the new RTH point later on, but i couldnt think of any harm flying for some couple of seconds in atti.

About doing what its programmed to do, sure thats what it did. Thats what it always does. Except that this behavior isn't documented anywhere, nor sounds logical to me at all. What seems logical is remaining in position as well as it could (GPS? Perfect!! No GPS, got optical focus? Use that! Got nothing? Run in atti mode!). Suddenly engaging an altitude limit? How is that an expected behavior??!

 

[dewster]

This is the way that DJI has decided to deal with "unauthorised" flight... e.g. when the Mavic doesn't know it's GPS co-ordinates and you are flying via OPTI, maximum altitude is 5M/16 feet. If you turn of VPS, then maximum altitude is 30M/98 feet. This was already demonstrated by an old Mavic video by someone who flew it off his balcony and the same thing occurred...

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The official DJI reply back then was that this issue is because the Mavic this guy had is a prototype and this won't happen with production Mavics... Official DJI Mavic ***Owner and Developer'sThread*** - Page 128 - RC Groups, but obviously, that's not true...

Big brother at the helm.

 

[borislip]

Big brother at the helm.

How does the big brother theory explain the difference between allowed altitude with and without VPS?

 

[Ozz]

My thinking is because its in Opti-Mode - it needs to sense where the ground is in order to keep stable.

You were too high up for the sonar etc sensors to see the ground correctly - so there is the max altitude warning.

This went away when it got the GPS fix.

 

[borislip]

My thinking is because its in Opti-Mode - it needs to sense where the ground is in order to keep stable.

You were too high up for the sonar etc sensors to see the ground correctly - so there is the max altitude warning.

This went away when it got the GPS fix.

Thata what i've assumed, AFTER seeing it happening. And i didn't expect that, what i did expect is a switch to atti after opti loses focus, not "descend and get opti back" behavior.

What if i'd fly high up in the air with GPS, and would lose it? Would it go opti and then descend just lile it did when launched in opti? This would be terrible!

 

[HFMan]

I think the reason altitude is limited is due to the ever imposing NFZ limitations. If you don't have GPS, they don't want you wandering into a NFZ at anything other than super low altitude.

 

[JLane]

Interesting. I already knew that height in OPTI mode is restricted to 5m (and 30m in ATTI) but I didn't realize that the Mavic would descend to that height if it suddenly found itself above that. Like you, I would have expected it to just fly in ATTI mode until it either got a GPS lock or you lower it manually into VPS range.

On a side note, I always thought the 5m restriction was odd and doesn't seem to be directly related to the capabilities of OPTI mode. For one thing, we know that the Mavic gives us VPS height readings up to 13m. Secondly, to record a precision home point, we are told to take the Mavic up to at least 10m. Seems to me like the Mavic is probably capable of flying in OPTI mode up to about 10m at least. It also doesn't make sense that the 5m limit is to do with unauthorized flight. If that were the case, they'd also limit ATTI mode to 5m, but they allow 30m.

 

[borislip]

Maybe the way precision landing works is by going to the GPS coordinates first, going down to 10m, and then using the VPS camera out of focus images it recorded while ascending in order to improve the landing precision. It wouldn't need to stay very precise at 10m, just get an approximate "lock". Being 1..2m off won't do much difference, and will bye corrected while descending, as the focus improves, so, technically, it is possible that the VPS stabilization altitude is way lower than a precision landing initial altitude.