Mavic crash against wall

[7thstring]

Hi all,

I'd like to hear from you to see if I made a mistake or if my drone is faulty.

I just got my MA Combo last Friday, previously had experiences with cheap drones, no GPS whatsoever.

After flying for a couple of hours in my backyard and in the park during the weekend, no issues whatsoever, even tried tracking and apas in trees, etc., yesterday I had the nice idea of trying to film my employees with the rocket preset.

I went on the terrace, noone around for safety, and tested the drone for a dry run to avoid injuries. The terrace is at the first floor between two 12m buildings.

I made a compass calibration as required by the app, checked the GPS quality (10 sats), used auto-takeoff (with precision mode if I recall) and started flying. As soon as I reached the top of the building a crow seemed to be irritated by the drone and started flying around it, possibly with the intention of attacking it. I therefore decided to land it for safety and after lowering the drone manually, I decided to demonstrate RTH to few employees observing from windows.

It all went fine until about 5 meters above: the drone went nuts and directed itself towards the wall of our building. I tried to cancel RTH to no avail (only later I learned that the quickest way is to toggle sports mode on/off), but also thought the front sensors would do their job. Needless to say (otherwise I wouldn't be writing this) that they didn't! And the drone crashed into the wall.

I managed to recover it by pulling the joystick backwards and downwards and hand-land it, so the only damage was to propellers, but I'd really like to know what went wrong.

The only mistakes I understand I made, apart from not being able to interrupt RTH are:
- failing to bring the side bumpers along (furthermore due to the intention to film my employees), perhaps that would have avoided the damage to propellers
- not checking if the RTH home was accurately set

But neither justifies the behaviour of the drone. Even if RTH home had been set inside the building by mistake (talking absurd), it should have not crashed into a concrete wall in my opinion. Unless there is a reason why RTH turns off sensors, which I believe shouldn't happen.

Log attached, after reading it I only see it went ATTI for a second, but otherwise GPS coverage was sufficient.

Thanks in advance for your comment and support, I would really like to know if it was the pilot's or drone's fault and in such case if I should have done anything differently, apart of the 2 points above.

 

[RayOZ]

Did you check the number of bars in the GPS signal? I assume you were between buildings, in shadows? GPS won't be very accurate if satellite signals are being blocked. I don't know for sure if shadows in building would affect obstacle avoidance.
I know using my phone's GPS to navigate in the city, the GPS is not very accurate when there are a lot of tall buildings around me. I assume it'll be the same with the MA.

 

[7thstring]

Sure I did, as per the report there were at least 10 sats as said below.

made a compass calibration as required by the app, checked the GPS quality (10 sats),

Sure the log show ditching to 4/5 sats for few seconds but that doesn't justify the glitch.

 

[HelloTello]

The probable cause for the crash could be the ATTI mode. The MA will change to ATTI mode with insufficient GPS coverage. All sensors and intelligent flight modes are disabled in this mode.

 

[7thstring]

It did switch to ATTI after the signal dropped and curiously VPS lost the reading, however for less than a second. May I suggest reading the log?

The interesting thing is that at 1'41.8" I seemed to stop RTH, therefore the only instant it went ATTI (at 1'42") it was already on its way towards the wrong home location (which by the map looks tob e correctly set when still on the ground and with 10/9 sats, after I the compass calibration ritual), doesn't look enough to permanently disable sensors, at least to my newbie eyes, does it?.

 

[RayOZ]

Sure I did, as per the report there were at least 10 sats as said below.


Sure the log show ditching to 4/5 sats for few seconds but that doesn't justify the glitch.

GPS quality does not equal to number of sats. I don't remember the details, but you can google search. If you are between buildings, your MA is can 'see' 10 sats, but they are close together that the accuracy is reduced.

 

[7thstring]

So basically between buildings better not to use RTH and only land manually?

 

[RayOZ]

I won't fly in close quarters where possible. It's like flying indoors, greater chance of crashes.
If you really want to fly between buildings, have Tripod mode on, and manually fly. If you read the manual, the RTH behaves differently depending on how for it is away from home point. So if GPS position is compromised, it might not behave the way you expect it.

 

[7thstring]

Thanks RayOZ, that's basically my learning. I thought I hadn't checked the home location properly but by the logs I did, but that's another learning as well.

I've gone through the manual mutliple times, also before purchasing the device (OT: this is the only reason why I was led to the Air instead of the Pro Platinum, which I already ordered) and this is the reason why I confidently pushed RTH, because I knew that given the low altitude and short distance it wouldn't have had to reach OTH height and I merely expected it to lower and adjust its position to reach the table I used to launch (it was more of a demo to colleagues than anything, I could have simply landed it myself... that's what makes me feel nervous about the situation).

 

[Jameslavis]

Ya I never use RTH. It’s a dangerous game and the sheer number of RTH incidents is pretty high. To me, it’s only use is to RTH on its own day it loses signal. I will never hit that ****.

 

[Maxheadspace]

So basically between buildings better not to use RTH and only land manually?

Before manufacturers came out with sensor avoidance, I lost several drones to RTH mishaps, such as snagging a tree that happened to get in the way. It taught me the habit of relying on RTH only as a failsafe, not as an option for bringing my drone back from a normal flight. I think it's still a good practice, and this incident is a good example.

 

[aokusman]

Before manufacturers came out with sensor avoidance, I lost several drones to RTH mishaps, such as snagging a tree that happened to get in the way. It taught me the habit of relying on RTH only as a failsafe, not as an option for bringing my drone back from a normal flight. I think it's still a good practice, and this incident is a good example.

100 percent with you. I have had my MA for two months and I have never used RTH. I try to fly LOS as much as possible and limit my distance to 4000 ft.

 

[7thstring]

Before manufacturers came out with sensor avoidance, I lost several drones to RTH mishaps

That's precisely what puzzles me though... the AIR indeed HAS sensors and didn't see a wall in front of it. On the Mavic Pro I see there is a toggle for enabling or disabling sensors during RTH (I think it was enabled by default), but on the Air I haven't seen anything like it.

 

[7thstring]

100 percent with you. I have had my MA for two months and I have never used RTH. I try to fly LOS as much as possible and limit my distance to 4000 ft.

With my Mavic Pro, just a week old, I went almost 2 kms away, beyond LOS obviously, and never engaged RTH. The issue with the AIR is that LOS or not, it's just not reliable. The connection is cr*p. I returned it, after I almost feared I could have lost it just because if was on the other side of the building (less than 100m away). Luckily failsafe RTH worked fine but I never had such issues with the Pro.

 

[InvisibleName]

That's precisely what puzzles me though... the AIR indeed HAS sensors and didn't see a wall in front of it. On the Mavic Pro I see there is a toggle for enabling or disabling sensors during RTH (I think it was enabled by default), but on the Air I haven't seen anything like it.

Yes you can disable the collision avoidance in Go 4 during RTH of the MA. Haven’t got mine with me, but I think it’s in the menu with the drone symbol

 

[7thstring]

Yes you can disable the collision avoidance in Go 4 during RTH of the MA. Haven’t got mine with me, but I think it’s in the menu with the drone symbol

Ok but it's enabled by default isn't it?

 

[InvisibleName]

Ok but it's enabled by default isn't it?

I believe so

 

[7thstring]

I believe so

So there is almost no explanation for what happened anyway... RTH failed but sensors should have prevented the crash. It deliberately went into the wall.

 

[melmartin]

I think taking off with 10 satellites is part of the problem. Personally, I would take off with at least 14. Around the forum some people say not below 11. It's not just the number of satellites, but their position. Satellites close to the horizon aren't likely to be good for navigation. The more you have, the more accurate your fix will be. I often get 17 flying here in Arizona, and that's a comfortable, reliable number.

 

[InvisibleName]

So there is almost no explanation for what happened anyway... RTH failed but sensors should have prevented the crash. It deliberately went into the wall.

If @sar104 takes a look at your log I’m sure he’ll confirm that you had a compass error cause your crash