Hi
I have a working f450 drone using a pixhawk 2.4.8 running copter 4.6.3
It has smart rtl failsafe set to 10.5v and it landed normally. The led turned yellow to indicate. The battery voltage actually climbed to 11.2v above the failsafe but the led was still yellow. I am actually able to even arm the drone but the led stays yellow. I also have video, I am attaching gdrive link
Please attach your parameters so that others can see your configuration. Have your tried rebooting the FC? I don’t think you can re-arm after the failasafe has occured even if the voltage rises back. Also, you won’t be flying any longer because the failsafe will kick back in in 10s as the voltage drops again while in flight
The failsafe is only cleared upon battery replacement. Otherwise you could get quite annoying transient recoveries that could disrupt manual recovery.
Arming with low battery isn’t inherently unsafe, especially if you have voltage telemetry. If you want to prevent arming there is BATT(x)_ARM_VOLT.
Yes the params are set correctly and it should not arm but it is able to arm which is wrong
The arm volt param is 10.8 if I remember
Even if the arming part is correct, the led should be blue or green to indicate ready to arm but it stays yellow which indicates not ready to arm as per the led codes
Yeah like I said, did you reboot the Pixhawk? I think once a failsafe kicks in you need to reboot even if conditions are met but I might be wrong
Be sure to use the Mission Planner initial parameters section to get the correct and exact voltage thresholds set to suit your battery type.
Yes I know the behaviour and it is set up corrxtly but I am just saying that the led behaviour is wrong according to me, yellow is failsafe then how is it able to arm and takeoff??
The arm volt is 11v, failsafe is 10.5 and crt failsafe is 10.3
Normal failsafe is land/smartrtl and crt failsafe is land
My question is not about flying since the voltage will sag and failsafe will trigger again or arming it, just the led behaviour
Does it become blue once you unplug and replug the battery? If so, I would think that is how it is intended to be
Led indicates that failsafe is active. Battery failsafe is not cleared unless the FC “knows” that the battery was replaced due to
a) being reset
b) receiving battery reset command when disarmed.
If failsafe is not cleared since I did not reboot or disconnect lipo etc how I am able to arm and throttle up
I think the intention is to show that the drone had hit a failsafe. You can arm because the voltage rose back up but the FC knows it had hit a failsafe. I think this is for situations like where if the pilot sees it turn back blue, they’ll think that it’s okay to fly again especially what they have is just a radio TX with no telemtry that would indicate a failsafe occured
Yes I meant that
But, it, according to me, should either not arm until battery replacement or led should turn to blue or green
It can cause accidents since pilot might turn off radio or something seeing it is not going to arm and then it randomly arms
Ardupilot doesn’t “randomly” arm. Especially if all the proper checks are turned on. That would detect the missing radio for example.
It would be handy if we could see the .bin log, but I suspect the same as what Lupus said - the LED indicates there WAS a failsafe.
From what I remember of the Arming code from last time I looked, arming is only prevented by current/active issues rather than something that resolved itself (battery voltage rose above arming voltage).
This is the log file and the video has already been attached in post 1
Battery failsafe is working as expected. The battery recovers quite a bit so you are able to arm again.
Be aware SmartRTL wasnt working because there was no valid position, and Land was the next option. RTL or any similar mode (Loiter) would have the same trouble.
The way that battery recovered from such a low voltage seems to indicate it might be too Low C for that copter, or it’s not getting fully charged. Either way I would stop using it once there is a battery failsafe and get it on charge before the next flight. Dont try to push it’s limits.
Exactly what battery do you have?
These are the correct voltage levels for 3S Lipo:
BATT_ARM_VOLT,11.00
BATT_CRT_VOLT,10.50
BATT_LOW_VOLT,10.80
If these give you an early failsafe then your battery is bad - dont change these values to try and correct for a bad battery or it will just get worse.
EDIT: 4 minutes is not a lot of flight time, you might want to get a better battery but keep the weight in mind or the motors will struggle.
For Arming checks I suggest you select everything except GPS, I assume this flight was indoor since there was no GPS signal at all.
In a future firmware version Arming checks are reversing : you will select the item you want to ignore. So that should be easier.
Really? Why not go to 3.3V per cell anyway. The OP will have need to get a new battery soon so let him as well enjoy a bit more flight time.. From the logs, I see only about less than 900 mAh was used out of 2200 mAh (although the max capacity should have gotten smaller now that the battery is old).
I thought the voltage limits would be lower for LiPos. I think the FPV world goes down to about 3.3V per cell
You could go lower with this copter if it wont fly very far away or high. The calculated values we use in MissionPlanner Initial Parameters and in the AMC allow for the copter to do an RTL after the low voltage trigger, or try to land when the critical voltage is reached.
With bigger payloads or longer missions even more conservative values have to be chosen if the RTL path is very long.
Famously a copter crashed into a boat in the UK after the pilot lowered the voltage failsafe levels to get more flight time, not allowing for how long the copter could fly (or not fly) once the low voltage was reached with a heavy broadcast quality camera on-board.
My spreadsheet (where the Initial Parameters came from) has a few battery types to select from, and also a conservative panel that may suit long-range missions or heavy payloads.
Download a copy of that sheet, dont try to use it online - it doesnt do that 
Sure… I forgot about RTL.