Maximum height with no GPS

[Borghi]

I was trying to do some flying at the bottom of a gorge and I didn't have a GPS signal. This was expected as there was very poor visibility of the sky. When flying I could only go 15 or 20 ft high and received a message stating that the height limit has been reached. What is the height limit if you cannot get a GPS signal? Is this something that can be changed in settings?

 

[old man mavic]

it is because the drone has no GPS that it relies on the downward sensors for indoor flying to keep it from moving all over the place in atti mode so it would seem that the same thing applies if it looses GPS outside as well

what you had to do was fly up the gorge till you aquired enough satellites to get your GPS back

 

[Mossiback]

Turning off the downward sensors should remove the limit that you hit. Having said that, make sure you can see it to maintain RC connection. If you lose GPS and connection with the RC consider it gone.

 

[old man mavic]

i dont think it is possible to turn off the sensors at this time on the MM

 

[Borghi]

I was just going to ask how to turn off downward sensors. I also have a Tello that has no GPS. I can fly up to 100 feet high using just downward sensors. I’m hoping I can do this on the Mini too. Of course I would keep the drone in line of sight. Needed the extra height so I could film a tall waterfalls.

 

[old man mavic]

I was just going to ask how to turn off downward sensors. I also have a Tello that has no GPS. I can fly up to 100 feet high using just downward sensors. I’m hoping I can do this on the Mini too. Of course I would keep the drone in line of sight. Needed the extra height so I could film a tall waterfalls.

what you could do to get the full waterfall is find a position and height where you can maintain GPS and then use the gimbal wheel to pan the camera slowly down to get the full length of the waterfall in, you could either go from bottom to top or top to bottom using that method

 

[DanMan32]

I was just going to ask how to turn off downward sensors. I also have a Tello that has no GPS. I can fly up to 100 feet high using just downward sensors. I’m hoping I can do this on the Mini too. Of course I would keep the drone in line of sight. Needed the extra height so I could film a tall waterfalls.

I don't think the VPS is effective that high on the Tello. You're pretty much in atti mode at that point.

 

[Keule]

What is the height limit if you cannot get a GPS signal?

The manual:

Is this something that can be changed in settings?

No

 

[chriscuk]

So if the downward sensors are active it'll go half the height of if they're not active BUT you can't de-activate them... daft
The other day I wanted to get the bird up in the air really quickly to take a look over a neighbors fence. I didn't need GPS but no matter what mode I selected I couldn't get the extra height to get past the trees so had to fly it the long way round down the street etc. By the time I got to their garden it got GPS and I came home the quick way.

- I needed to look into their garden as their house alarm was going off and wanted to see if anyone was in the back of the property.

 

[scro]

I don't think the VPS is effective that high on the Tello. You're pretty much in atti mode at that point.

I've got a Tello and it is usually pretty good at keeping VPS active at 30m altitude. The only times I've seen VPS drop out is if it's too dark or the AC flies over featureless ground (eg smooth grass, snow or water), and in these circumstances VPS loss can happen at much lower altitudes.

The MM's VPS allegedly works to 30m altitude max (ref pg 15 of the manual)

 

[old man mavic]

So if the downward sensors are active it'll go half the height of if they're not active BUT you can't de-activate them... daft
The other day I wanted to get the bird up in the air really quickly to take a look over a neighbors fence. I didn't need GPS but no matter what mode I selected I couldn't get the extra height to get past the trees so had to fly it the long way round down the street etc. By the time I got to their garden it got GPS and I came home the quick way.

- I needed to look into their garden as their house alarm was going off and wanted to see if anyone was in the back of the property.

i didnt need GPS that statement says it all really,because you took off without a GPS lock ,the drone was in atti mode and there for you were restricted to the reduced height requirement, if there were no vision sensors as soon as the MM hade gone up over the trees and there had been any wind then it would have been blown off course you should never fly before you have a GPS lock if you had waited a few seconds longer until the GPS and the homepoint message had been given you could have flown up over the trees and got to the garden quicker

 

[chriscuk]

I've had the drone sat in the middle of my driveway for a couple of minutes (easily 2, sometimes 5) without GPS lock and the same for the field where I usually fly (more like 90secs -> 2mins). I've flown the drone around the house enough to have an okay grasp of how it moves without the GPS assistance. As for the windit would have been unfortunate but it was a calm day with virtually no wind. I also wasn't getting 15 or 30m in height as that'd have been easily enough to clear the house or trees. I was stuck at more like 6-8m and this was over grass. I only needed to clear two gardens and one row of trees on my garden

I have been getting a lot of sensor issues recently which isn't filling my with confidence and sometimes it's quite noticeably dropping altitude when flying. Not something you'd see on the screen or the height display but it's rather obvious when you're looking at it that it'll often drop a couple of meters vertically before climbing again. I was doing a quick test on the driveway hovering at 2m and checking the stats it showed that at one point it was 4m above the ground and another it had dropped to 1.2m. All through this time it was relatively stationary. It might have moved 10cm in either direction but no more.

My first few flights where I was happy to send it out far or up high have now been left with wanting to just keep it close until I figure out what is wrong with its positioning.

 

[old man mavic]

the drones ability to get a GPS lock is dependant on the no of visible sats that it can detect in an urban environment this ability is greatly reduced by the proximity of buildings and also you could be getting magnetic interference from the surroundings as well if you stood very close to your car it can give a magnetic interference message because of the metal in the car you shouldnt have to keep doing the compass calibration if you get a good result when you are out in a none urban area i have only calibrated my MPP once in over a year and have flown in many different places during that time but please dont take off untill you get the green light on the app and the message about the home point it is important if you want to have a safe and trouble free flight just trying to help you thats all

 

[Dave Maine]

Also recall that the satellite fix in any location is constantly changing as the source satellites move around constantly. The drone monitors all of this, and will swap satellites in and out as the geometry changes. This is not a problem with the drone. It is the basic nature of GPS navigation systems. The location, from a GPS perspective, is rarely the same twice.

This variability is partially behind DJI’s mandate of a minimum number of satellites before allowing GPS based flight. To get an accurate XYZ location only requires 3 satellites if you have a perfect geometry and clear sight lines between the drone and satellite.

 

[chriscuk]

I appreciate that you are trying to help but I am fully aware of urban environments impacting GPS reception much like cloudy weather has an impact. Some of my tests that have taken over 2 minutes to get a GPS lock have been in a field a good 100m from any buildings and the only RF noise that I could pick up on the drone or my phone was my home WiFi. I didn't check for noise on 1.2ghz or 1.5ghz but it's the lock time that is really annoying I find. I sat there watching it go 5->9->10->12->9->10->12 satellites. I'm not sure but maybe the more expensive models have a-gps or something that gets them a better lock speed. If they at least cache its location they might get an assisted GPS log to help speed up location finding. It's why phones can get a much quicker lock as they'll have a complete database to cross reference rather than pure triangulation of the signals.

I take off from this point normally.

 

[scro]

Realtime uncorrected GPS positioning can be accurate to 1-2m at best, provided you have a signal from multiple satellites. You can get a location with just 3 satellite signals, but the accuracy isn't great (>10m typically) and no use for maintaining the position of a hovering drone. That's another reason why DJI require far more than just 3 satellites for GPS.

Survey grade GPS units can give cm level accuracy, but they need a static ground-based reference station for error correction.

Drones typically use VPS (and possibly inertial sensors) in conjunction with GPS to get better hovering accuracy. See the hovering accuracy specs that DJI publish and they typically quote +/-1.5m for GPS only, improving to +/-0.1m with VPS.

 

[old man mavic]

I appreciate that you are trying to help but I am fully aware of urban environments impacting GPS reception much like cloudy weather has an impact. Some of my tests that have taken over 2 minutes to get a GPS lock have been in a field a good 100m from any buildings and the only RF noise that I could pick up on the drone or my phone was my home WiFi. I didn't check for noise on 1.2ghz or 1.5ghz but it's the lock time that is really annoying I find. I sat there watching it go 5->9->10->12->9->10->12 satellites. I'm not sure but maybe the more expensive models have a-gps or something that gets them a better lock speed. If they at least cache its location they might get an assisted GPS log to help speed up location finding. It's why phones can get a much quicker lock as they'll have a complete database to cross reference rather than pure triangulation of the signals.

I take off from this point normally.

maybe you have a problem unit i have never waited that long out doors to get a lock i find that the drone needs around 10 before it gives the go ahead to fly ,i will say though that i think that DJI have erred on the side of caution with the MM compared to my MPP probably because of the lack of any sensors i can get my MPP to get a GPS lock in my living room near to the window it takes a little time but i can get up to 10 sats and the ok to take off message ,but,on the MM the best it has managed to lock on to is 4 in the same location

 

[chriscuk]

I think its just completely different hardware. All the way though the product lineup they detail the GPS unit's refresh rate and the expected maximum lock time.
I did fly somewhere the other day that was obviously a silly place. I was close to water, very large bridges and the place I decided was a good take off point was clearly a very large slab of concrete over something metal. I put the device down and waited a while but got zero GPS and a number of sensor errors and compass issues. As I picked it up to walk away the compass errors stopped almost instantly and then GPS started to come back.

When people talk about the massive accuracy of phone GPS they dont realise that most of this accuracy is actually GPS overlayed with the gyro to get better data. Higher refresh GPS devices are actually rather expensive. A phone as an example generaly has a 1hz gps module but people will use 0-60 apps that register to 100ths of a second. I've got a dedicated 10hz unit with gyros that gives better data but this simple device was rather expensive too.

I'd guess the DJI lineup differs in similar ways with the more expensive modules having more sensitive receivers and faster cold starts. I've not actually checked the warm start time for the mini - it might not even cache anything so wont have any form of warm start.

I'm now having memories of my old Flytrex data logger :O

 

[old man mavic]

i know what you are saying i purchased a spare gps module for one of my early drones as it was going cheap from bangood when it arrived i noticed it had a tiny battery similar to a watch battery attached to the board did some research and found that the GPS stores the sat info at any given point in a memory chip so it helps it to know where the sats are in the sky and it locks on to them quicker ,is it possible that to save some weight they have removed the battery on the module for the mini just a thought

 

[Mossiback]

...Some of my tests that have taken over 2 minutes to get a GPS lock have been in a field a good 100m from any buildings...

My MP gradually took longer and longer to switch into GPS mode. It had been a while since I have performed any calibrations so I decided to calibrate the IMU, which fixed my problem. My MP once again will rapidly switch into GPS mode.

I do not know if this will work on the MM.