FS_option logic to avoid crash

I just had a couple of crash due to current setting on FS logic. Here the events:

  • Drone has low battery voltage: RTL is triggered and aircraft starts to climb
  • pilot abort RTL by changing flight mode to Loiter
  • Drone has now critical battery voltage, LAND is triggered and aircraft start to descent ( let’s says from 10m)
  • RX lost link and system read RC fail-safe ( sbus trigger fail-safe), drone start RTL procedure, climb back to 20m then battery is too low and crash.

I would like to change setting is such a way that if system is already in land mode, will continue but also if battery is OK and RX lost link, normal RTL is triggered.

As alternative, change setting in such a way that if critical battery voltage is triggered, RTL from fail-safe is ignored

@rmackay9 could be this a bug? Rx failsafe with RTL get higher priority that critical battery failsafe that is set to Land mode

The flight controller did exactly what it was supposed to.

Your mistake was aborting the original Low Battery RTL.

Sorry but I don’t agree. If system is in critical low battery, RC failsafe should be ignored or at least have the option to do


Think about what you are saying…

If a if a low battery fail safe is over ridden by a loss of RC fail safe you want to be able to switch back the the low battery Ffail safe so the aircraft will land.

You cannot do that because during a loss of RC, the RC link is NON OPERATIONAL.

If you disable the loss of RC fail safe, during a loss of RC condition the aircraft will continue to fly all of the way to the scene of the crash.

The bottom line is, it is apparent to me that you have the low battery fail safe set too low. This leaves insufficient battery capacity for a safe RTL.

There is an option already exists just for the case you faced
See the “Continue if landing on any failsafe”. If you set this flag then any failsafe will be ignored if you in LAND mode.

LOL. I’ll have to remember that one :grinning:


I don’t want switch anything. I want that if system is in land mode due to failsafe, it should ignore Rx failsafe set for RTL.

@sergbokh can you confirm that with fs_options “continue if landing on any failsafe” system will act as I need ?

I think so. It was introduced to cover at least following scenarios:

  • If operator has manually switched to LAND, then he indeed want the vehicle to land and don’t want landing to be interrupted by RC failsafe (that is pretty possible if landing away of the operator location)
  • If LAND is engaged by a failsafe event

I personally tested the 1-st scenario, but not 2-nd.

Many thanks! Will change the parameter and test with land trigger by RC and triggered by failsafe

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@sergbokh This gas been tested just now.

I can confirm that Land mode doesn’t change with both GCS triggered and failsafe triggered RTL

Log to the file for confirmation https://drive.google.com/file/d/1DGjoDLZsqpZOb5YLouRJAHg16K7nKolh/view?usp=sharing

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No , i think you are miss understand , you said critical batter after Rx failsafe it means you change rtl when battery is critical and after Rx fs so it means once again rtl proceed.

Yesss it’s absolutely right

Regarding less the low or critical battery failsafe, if in failsafe and Land mode is selected, with the correct fs_option is possible to act in such a way that Rx RTL failsafe is ignored

Go to fs option and set Rx lost = land mode problem solve

I am thinking out loud, but maybe it could be discussed, as some work has been done but it seems that it is not completely consolidated. There could be a fs inheritance, that could go from hover, srtl, rtl, land… so if one system triggers a more strict type of fs then it changes from one to another. If the fs type is less strict in this inheritance, ghen it is not changed. It could be the same for not allowed modes. In this case if the system cannot change to smart rtl then automatically it would change to the next more strict mode, maybe rtl. Then the fs options could be easier to set.

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Like all safety features, fail safes are there for a reason and each has its own priority for a reason.

IMHO, defeating ANY safety feature demonstrates a reckless disregard for the safety of others.

You do what you like. I’m not having any part of it.

this doesn’t make any sense, because in case of RC failsafe while with good battery, i could lost the drone

I think you didn’t get my point.
I would let choose any fs option, as it is now, but if two failsafe modes are triggered, the selected mode should not be the last triggered, but the most restrictive.

If battery is critical low RTL shouldn’t be launched at all if it requires to climb. As I understand You are trying to cover scenario when battery is getting low and You are far far away from launch site and are forced to land somewhere else. Lowering the altitude is causing RX loss in this case?

Correct, and this is solved by setting fs_option to “continue if landing on any failsafe