Smart RTH may be stupid (warning)

[larkin]

So, I turned on Obstacle Avoidance for the first time since my first flight. I did so because I wanted the Mav to watch itself while following us around in the park in active track mode. Just moments before, it was hovering like a champ in 20mph winds. After turning OA on and lifting off, the Mav immediately started to drift away uncontrollably and almost smacked into a concrete wall.

Why did it do this? Because Obstacle Avoidance is stupid. It is! Instead of limiting the Mav's forward ground speed to 15mph, which it needs to do for the front sensors to process and for the Mav to react fast enough to avoid obstacles, it limits the thrust that the props will produce to push the Mav in that direction. A forward movement speed limit of course should not affect its ability to maintain a stable hover in the wind. But it does.

So I always turn off OA as a safety precaution. But I'm here to deliver another warning I just realized is necessary. Even after turning off OA, Smart RTH is still enabled. This is a toggle in advance settings which turns on OA in the event of RTH (either the user pressed the RTH button or the drone disconnected from RC and RTH was the default action). This means if it's windy outside and your RC gets disconnected, you may never see your drone again.

Needless to say, I've disabled both OA and Smart RTH until DJI address this with a firmware update.

Sent from my XT1650 using MavicPilots mobile app

 

[Strafe1]

I don't have your issue. OA is almost always on and I have stable hover with or without wind. It's almost as if you turned of VPS sensors also. I don't think this is a generalized Mavic problem. Maybe some sort of interference?

 

[Robbyg]

I have OA on and have never had an issue like that in 15MPH winds. I have even put it into tripod mode and as expected it stayed still in heavy winds.

 

[Filmscum]

I also don't have this issue. Yes it limits the forward speed to 20mph and in a strong headwind that speed is diminished but with sensors on my mavic can and does indeed maintain a solid hover. Yes in windy conditions it isn't totally rock solid but mine in no way gets pushed around. Like Strafe1 said maybe check your VPS sensors?

 

[JLane]

Why did it do this? Because Obstacle Avoidance is stupid. It is! Instead of limiting the Mav's forward ground speed to 15mph, which it needs to do for the front sensors to process and for the Mav to react fast enough to avoid obstacles, it limits the thrust that the props will produce to push the Mav in that direction. A forward movement speed limit of course should not affect its ability to maintain a stable hover in the wind. But it does.

I think the problem is that, not only is forward speed an issue (for reaction times) but also forward pitch angle. The front sensors will work only up to a particular amount of forward pitch (16 degrees as per the manual). I think with any further pitch the front sensors will be pointing too much towards the ground, and won't properly sense objects in front. Given that limitation, the Mavic can't simply increase thrust to maintain forward speed, because if it increases thrust without also increasing forward pitch, it will end up ascending.

 

[Kilrah]

Instead of limiting the Mav's forward ground speed to 15mph [...] it limits the thrust that the props will produce to push the Mav in that direction

No, it limits pitch angle since cameras can't see forward at same height anymore if tilted too much. Pitch angle limitation results in airspeed limitation.
Ground speed has nothing to do with it.

 

[WolfgangStiller]

Rather than turn off OA (which means clicking through the menus) if you think the winds are too strong, just click the Sport mode switch (fast and easy). This does two things: disables OA and provides much faster max speed to fight strong winds. You can also quickly click from sport to P mode to get the benefit of OA again.

 

[Cyberpower678]

Don't have this issue.

 

[larkin]

Rather than turn off OA (which means clicking through the menus) if you think the winds are too strong, just click the Sport mode switch (fast and easy). This does two things: disables OA and provides much faster max speed to fight strong winds. You can also quickly click from sport to P mode to get the benefit of OA again.

The thing with that is you can't take-off in Sport mode and as soon as the thing starts to drift away the human goes into oh **** mode and it's hard to think to switch Sport on, but a good suggestion if you're high in the air already and the wind picks up.

Does the Mavic stay in sport mode though during RTH?

I think the problem is that, not only is forward speed an issue (for reaction times) but also forward pitch angle. The front sensors will work only up to a particular amount of forward pitch (16 degrees as per the manual). I think with any further pitch the front sensors will be pointing too much towards the ground, and won't properly sense objects in front. Given that limitation, the Mavic can't simply increase thrust to maintain forward speed, because if it increases thrust without also increasing forward pitch, it will end up ascending.

No, it limits pitch angle since cameras can't see forward at same height anymore if tilted too much. Pitch angle limitation results in airspeed limitation.
Ground speed has nothing to do with it.

The incline explanation makes a lot of sense. It also confirms that in certain circumstances, OA can work counter to safe flight.

Still gonna leave it off.

 

[JLane]

The incline explanation makes a lot of sense. It also confirms that in certain circumstances, OA can work counter to safe flight.

Still gonna leave it off.

Agreed. Although I've never had the problem with overpowering head winds, I have heard of people having the issue. OA is definitely not perfect, and I think a lot of us are finding that it's not quite the bee's knees that we thought it would be. I think I'll be leaving mine switched off, too.

BTW... Yes, the Mavic will perform the RTH in Sport mode if it's switched on (at least that's what I've heard many times from others who've tried it).

 

[WolfgangStiller]

The thing with that is you can't take-off in Sport mode and as soon as the thing starts to drift away the human goes into oh **** mode and it's hard to think to switch Sport on, but a good suggestion if you're high in the air already and the wind picks up.

Does the Mavic stay in sport mode though during RTH?



Still gonna leave it off.

I can take off in Sport mode just fine but you can switch to Sport just after take off so you can benefit from the OA sensors during take off. yes, it will fly in sport mode during RTH.