(Warning) Avoid this low battery RTH mistake

[Zdude70]

i never, ever shut the r/c or transmitter off while the vehicle (drone in this case) is on.

i had a friend make that mistake with my 14+ pound r/c truck. the lipos in the truck started getting low, i suggested we power it down to swap the batteries out, and he turned the transmitter off before i could get to the truck. it immediately took off, launched over a curb and got stuck in a neighbor's fence.

for me, it's always r/c power first, then the vehicle. on startup. reverse that on powering down.

 

[fran1o86]

Does anyone of you mess up with the RTH setting to set it to the controller location instead of take off location? Would have probably helped in this situation

 

[dbyantis]

Lol, if I may: You don't necessarily need to be a noob to abort RTH and land elsewhere if your battery is insufficient to make it back to home point. I believe the question here is did the Mavic take off on it's own after an aborted RTH?

This situation is more likely that the Mavic was still props spinning, when the RC was turned off, that initiated RTH for disconnect, not low battery, low battery was hit on the return flight, the Mavic will estimate the power needed to RTH, it is not clear if the estimate was correct at the time RTH initiated so Mavic may have assumed that it could make it home on disconnect and started that return, during the return battery ran low.

 

[Lake_Flyer]

This is proving to be quite an interesting topic.

Indeed.
I realise I shouldn't have been that grumpy to you. This is a great topic and a good learn.

Cheers
Jan

 

[rfc]

Maybe not. Looks like @Yannie ran into the problem that a lot of pilots (including me) have run into. For FW > 01.03.0900 the desired flight doesn't show up when using the DJI Assistant.

Doesn't the bird just show up as a drive in Windows (or Mac) when you plug it in to the 'outer via USB? It's been a while since I did it, but I thought I didn't even have DJI Assistant at the time, and just dragged the .dat files across.
Converting them/using them is another matter, but are they just gone after 01.03.0900?

 

[Qoncussion]

@Yannie ~ As I'm going to be testing this, I would like to get some more information from you about your settings. Do you know what your "low battery", and "critical battery" trigger values were set to? I know that the Mavic defaults to 30% for low battery, but you said you were at 18%, with no mention of the RC beeping when you landed near your car.

Can you post your logs? It's quick and easy to do. Just follow the instructions here:

DJI Flight Log Viewer

 

[Lapeer20m]

Nope. He is right. Not only the FAA, but also for hobbyist flying under Sec 336.

This applies specifically to part 107....from FAA advisory circular 107

"However, the person maintaining VLOS may have brief moments in which he or she is not looking directly at or cannot see the small UA, but still retains the capability to see the UA or quickly maneuver it back to VLOS. These moments can be for the safety of the operation (e.g., looking at the controller to see battery life remaining) or for operational necessity. For operational necessity, the remote PIC or person manipulating the controls may intentionally maneuver the UA so that he or she loses sight of it for brief periods of time. Should the remote PIC or person manipulating the controls lose VLOS of the small UA, he or she must regain VLOS as soon as practicable. For example, a remote PIC stationed on the ground utilizing a small UA to inspect a rooftop may lose sight of the aircraft for brief periods while inspecting the farthest point of the roof. As another example, a remote PIC conducting a search operation around a fire scene with a

small UA may briefly lose sight of the aircraft while it is temporarily behind a dense column of smoke. However, it must be emphasized that even though the remote PIC may briefly lose sight of the small UA, he or she always has the see-and-avoid responsibilities set out in part 107....."

The FAA recognizes that you may sometimes not ybe able to maintain sight of the aircraft and under Certian circumstances this is still keeping within the guidelines.

https://www.faa.gov/uas/media/AC_107-2_AFS-1_Signed.pdf

 

[BudWalker]

Doesn't the bird just show up as a drive in Windows (or Mac) when you plug it in to the 'outer via USB? It's been a while since I did it, but I thought I didn't even have DJI Assistant at the time, and just dragged the .dat files across.
Converting them/using them is another matter, but are they just gone after 01.03.0900?

Maybe you're referring to the external/removable SD card which just contains the stills and videos. It behaves like you described - after plugging in the USB cable a drive appears on the PC that is that external SD card.

The .DAT files are on a internal SD card and require the DJI Assistant 2 to see and retrieve them. Speaking for myself and at least some others .DAT retrieval has gotten progressively harder since 01.03.0900. I don't know if every Mavic owner has experienced this. DATs that you know should be there don't appear. Sometimes on subsequent DJI Assistant starts a missing .DAT will magically appear. Sometimes a .DAT that was appearing will go away. I've heard some say the problem was a driver issue and could be fixed with a procedure to remove and re-install drivers. I tried this and it seemed to help for a while - could just be a coincidence though.

There is also the fact that the newer Mavics don't have an internal SD and the .DAT files are saved on the internal flash drive. But, mine has the internal SD so I'm not sure what's happening.

 

[Yannie]

@Yannie ~ As I'm going to be testing this, I would like to get some more information from you about your settings. Do you know what your "low battery", and "critical battery" trigger values were set to? I know that the Mavic defaults to 30% for low battery, but you said you were at 18%, with no mention of the RC beeping when you landed near your car.

Can you post your logs? It's quick and easy to do. Just follow the instructions here:

DJI Flight Log Viewer

Hi guys, I'll keep this response quick:

a) I've been reluctant to post my flight logs because it reveals too much private information. (Please see below)
b) There were no DAT or TXT files on the drone SD card. I have already analysed all the DAT and TXT files found on my phone. As you'd expect, these logs stopped the moment I disconnected my drone.
c) On the whole, I've found DJI Assistant 2 very useless. I'm not able to see any data within the app (should I be able to?). I can just export black box data.

Here is the flight log of the flight.
This flight was about 6 weeks ago, with many uneventful flights since. You'll have to forgive me if some of my earlier recollection of the event was inaccurate in my initial post.
I have deliberately removed all the GPS coordinates for confidentiality.
What I can tell you is: the take-off point was also the 'home point'. The landing point was not the home point.

https://docs.google.com/spreadsheets/d/1RNXHUiKRyH-5iIKl0PrN-f38RCmQir5np8ApCzAixKU/edit?usp=sharing

As I mentioned before, these logs are from my phone. The logging stopped once my phone was disconnected. There is nothing on the drone's SD card. I haven't been able to extract anything useful from the DJI Assistant 2 app.
- I am interested in what information is held in the TLV, MAP and INFO files in the Analytics directory. I have files with these extensions which have a later time stamp than the rest. Maybe they will provide more information.

I look forward to seeing what comes of this and whether other people can reproduce this event.

Cheers,

Yannie

PS Lake: Thank you, no hard feelings. I'm sorry for my part too!

 

[BudWalker]

The OP posed the question pertaining to a low battery and would the Smart Battery system fly it back home even after it had landed. A few posters asked about a related question - would a RC disconnect cause the Mavic to RTH even after landing. I tested this.

If the props have stopped then a RC disconnect will not cause an RTH. Here the pink area is an RC disconnect. The motors stay stopped.


But, if the Mavic has landed and the props are still running a RC disconnect will cause an RTH. Here the motors are idling. After 3 secs of RC disconnect (pink area) RTH is initiated (brown area) and launch occurs.

 

[Yannie]

Maybe you're referring to the external/removable SD card which just contains the stills and videos. It behaves like you described - after plugging in the USB cable a drive appears on the PC that is that external SD card.

The .DAT files are on a internal SD card and require the DJI Assistant 2 to see and retrieve them. Speaking for myself and at least some others .DAT retrieval has gotten progressively harder since 01.03.0900. I don't know if every Mavic owner has experienced this. DATs that you know should be there don't appear. Sometimes on subsequent DJI Assistant starts a missing .DAT will magically appear. Sometimes a .DAT that was appearing will go away. I've heard some say the problem was a driver issue and could be fixed with a procedure to remove and re-install drivers. I tried this and it seemed to help for a while - could just be a coincidence though.

There is also the fact that the newer Mavics don't have an internal SD and the .DAT files are saved on the internal flash drive. But, mine has the internal SD so I'm not sure what's happening.

Thanks BudWalker. I have a standard Mavic Pro (not platinum). I use the external SD card slot within the drone. My current understanding is that this device also has internal data storage for the black box data, is this correct? If you ever find a way to get the DJI Assistant 2 app working properly, please let me know!

 

[Yannie]

Hi guys,

I had a near miss. I just wanted to alert you of this so nobody loses their Mavic Pro.

I was filming a lake.
I parked my car on one side of the lake and I launched my drone from the opposite side of the lake.

I completed my filming and knew the drone's battery was pretty low at around 18%. Time to wrap things up.
I thought I would be clever and just land my drone near my car, so that I didn't need to carry it back to the car.
I landed it via the video feed and confirmed that it was actually stationary on the ground.

I unplugged my phone and turned off the Mavic controller. I completely packed everything away.

After about 5 minutes, after walking halfway back to the car, I suddenly heard my Mavic in the air!!

Confused and freaking out, I opened my bag and turned on the controller on again (without a smartphone). As soon as it connected to the drone, it immediately starts beeping, indicating that the battery was now very very low (eg, single-digit %)

Because the battery had dropped to a certain level while it sat idle on the ground beside my car, it had autonomously taken off again, climbed to the RTH altitude I previously set (100m) and heading 'home', over the middle of the lake.

It didn't have enough battery to make it home. Mid-way through it's RTH course over the lake, the battery reached the critically-low threshold and it began doing an forced-decent over the middle of the lake.

I could not override this descent - however I was fortunate on this occasion because I had a physical line-of-sight to the drone from where I was standing. I was even more fortunate that I was able to manually roll the drone sideways and steer this forced-descent onto a patch of dirt which happened to be beside this particular section of it's RTH course.
(again, my phone wasn't plugged in to the controller so I had no video feed; it was all manual)

On this occasion the drone wasn't destroyed, but this was a very, very close call.

I understand that the drone will return to home on low battery and lost signal...but I was surprised that it will do this even after the pilot has landed it somewhere else. This seems to be a loop-hole in the RTH algorithm.

If I ever want to land the drone at an alternative site, how can I land it and STAY THERE, even when the battery gets low? (assume I'm flying using just the manual controls, ie, without a smart phone)

Has this happened to anyone else?

Please be careful of this, guys.

EDIT:


Here is the flight log of the flight.
This flight was about 6 weeks ago, with many uneventful flights since. You'll have to forgive me if some of my earlier recollection of the event was inaccurate in my initial post.
I have deliberately removed all the GPS coordinates for confidentiality.
What I can tell you is: the take-off point was also the 'home point'. The landing point was not the home point.

DJIFlightRecord_2018-01-03_(11-39-13) (GPS coordinates removed).xlsx

 

[787steve]

This applies specifically to part 107....from FAA advisory circular 107

"However, the person maintaining VLOS may have brief moments in which he or she is not looking directly at or cannot see the small UA, but still retains the capability to see the UA or quickly maneuver it back to VLOS. These moments can be for the safety of the operation (e.g., looking at the controller to see battery life remaining) or for operational necessity. For operational necessity, the remote PIC or person manipulating the controls may intentionally maneuver the UA so that he or she loses sight of it for brief periods of time. Should the remote PIC or person manipulating the controls lose VLOS of the small UA, he or she must regain VLOS as soon as practicable. For example, a remote PIC stationed on the ground utilizing a small UA to inspect a rooftop may lose sight of the aircraft for brief periods while inspecting the farthest point of the roof. As another example, a remote PIC conducting a search operation around a fire scene with a

small UA may briefly lose sight of the aircraft while it is temporarily behind a dense column of smoke. However, it must be emphasized that even though the remote PIC may briefly lose sight of the small UA, he or she always has the see-and-avoid responsibilities set out in part 107....."

The FAA recognizes that you may sometimes not ybe able to maintain sight of the aircraft and under Certian circumstances this is still keeping within the guidelines.

https://www.faa.gov/uas/media/AC_107-2_AFS-1_Signed.pdf

Exactly correct. I forgot about the brief exceptions. I thought you might be thinking that VLOS was not a player for hobbyists, which would be incorrect. My bad.

 

[rfc]

Maybe you're referring to the external/removable SD card which just contains the stills and videos. It behaves like you described - after plugging in the USB cable a drive appears on the PC that is that external SD card.

The .DAT files are on a internal SD card and require the DJI Assistant 2 to see and retrieve them. Speaking for myself and at least some others .DAT retrieval has gotten progressively harder since 01.03.0900. I don't know if every Mavic owner has experienced this. DATs that you know should be there don't appear. Sometimes on subsequent DJI Assistant starts a missing .DAT will magically appear. Sometimes a .DAT that was appearing will go away. I've heard some say the problem was a driver issue and could be fixed with a procedure to remove and re-install drivers. I tried this and it seemed to help for a while - could just be a coincidence though.

There is also the fact that the newer Mavics don't have an internal SD and the .DAT files are saved on the internal flash drive. But, mine has the internal SD so I'm not sure what's happening.

Could DJI be intentionally doing this, to keep this potentially valuable "post incident" information in their hands only? I'd consider downgrading firmware for the sole purpose of being able to pull a dat file off the bird.

 

[Qoncussion]

The OP posed the question pertaining to a low battery and would the Smart Battery system fly it back home even after it had landed. A few posters asked about a related question - would a RC disconnect cause the Mavic to RTH even after landing. I tested this.

If the props have stopped then a RC disconnect will not cause an RTH. Here the pink area is an RC disconnect. The motors stay stopped.
View attachment 31211

But, if the Mavic has landed and the props are still running a RC disconnect will cause an RTH. Here the motors are idling. After 3 secs of RC disconnect (pink area) RTH is initiated (brown area) and launch occurs.
View attachment 31212

I too tested this in the field today, and reached the exact same conclusion - minus the pretty charts .

I also found when all of my sensors were on, including the landing protection option, the drone always knew when it had landed and killed its own motors immediately (no 1, 2 or 3 second lag - immediately) (ok, maybe a 1 second lag). However, when the bottom sensors were disabled, the motors continued spinning after touchdown, and an RC disconnect triggered a full on RTH.

I got some insight as to the state of the drone during one of the tests. I have just always assumed that when the craft is on the ground, under any circumstances, it would remain there until acted on by programming (shutdown motors or RTH) or by an RC command. With the bottom sensors off, the Mavic still thinks that it's flying. After one of the landings, with the props idling away at around 1,700 RPM, they began to idle-up - it started rising and slightly altering its position, about a foot off of the ground, moving in small increments from side to side; behaving just as it would in flight while trying to maintain its position in 3D space.

So finally, I landed with the sensors off, killed the motors and disconnected the RC. Once again proving that it will not autonomously fire up and attempt to do anything, if the motors are off.

 

[joejaxvic123]

Well done, guys!

 

[Yannie]

I too tested this in the field today, and reached the exact same conclusion - minus the pretty charts .

I also found when all of my sensors were on, including the landing protection option, the drone always knew when it had landed and killed its own motors immediately (no 1, 2 or 3 second lag - immediately) (ok, maybe a 1 second lag). However, when the bottom sensors were disabled, the motors continued spinning after touchdown, and an RC disconnect triggered a full on RTH.

I got some insight as to the state of the drone during one of the tests. I have just always assumed that when the craft is on the ground, under any circumstances, it would remain there until acted on by programming (shutdown motors or RTH) or by an RC command. With the bottom sensors off, the Mavic still thinks that it's flying. After one of the landings, with the props idling away at around 1,700 RPM, they began to idle-up - it started rising and slightly altering its position, about a foot off of the ground, moving in small increments from side to side; behaving just as it would in flight while trying to maintain its position in 3D space.

So finally, I landed with the sensors off, killed the motors and disconnected the RC. Once again proving that it will not autonomously fire up and attempt to do anything, if the motors are off.

Thanks very much for doing these experiments guys.

Would the drone behave differently if you descended to the ground with Sports Mode on compared with Sports Mode off?

What about the flying modes in the DJI GO app, such as Cinematic mode, Tripod mode, etc?

Also, when your sensors were disabled, are you able to confirm whether the drone continued storing logs and other data on it's SD card after the controller disconnected (and while it did the connection-lost RTH sequence)?

These sensor findings have really got me wondering...

Very interesting indeed!

 

[kidroc]

always use the auto landing then you have no worries.

 

[Lake_Flyer]

Could DJI be intentionally doing this, to keep this potentially valuable "post incident" information in their hands only? I'd consider downgrading firmware for the sole purpose of being able to pull a dat file off the bird.

They do everything for a reason. It is all part of a very well thought out strategy.
By doing this they prevent crash data (and possible clues to specific DJI IP) to end up at the web for everybody (and the competition) to study.

 

[BudWalker]

Could DJI be intentionally doing this, to keep this potentially valuable "post incident" information in their hands only? I'd consider downgrading firmware for the sole purpose of being able to pull a dat file off the bird.

Well there is no way to know for sure what DJI's intentions are. But, my impression is that these changes have nothing to do with preventing users from looking at the .DATs. Rather the changes were made for some other purpose and DJI just isn't concerned with providing continued user access to the .DATs. It's not clear to me that access to the .DATs isn't possible with the right set of drivers/OS/etc. And, if preventing user .DAT access was the goal then it certainly could be made much, much harder.

I happen to have two Mavics. One is on the latest FW. The other is permanently on FW 01.03.0700 just for the purpose of being able to retrieve .DAT files.