this has been bugging me for two days and i cant figure it out. was doing a slow cruisy flight in my backyard, like barely moving, just hovering at maybe 2 meters and the thing just dropped. no beeping, no low battery warning, just fell straight down. lucky it landed in the grass and nothing broke but now it wont arm at all.

betaflight connects fine, i can see all the sensor data, receiver is showing inputs correctly, everything looks normal on the screen. but when i try to arm i get the red light staying solid and nothing happens. checked the arm switch about a hundred times. its a 4s setup if that matters, was at maybe 3.7v per cell when it dropped which shouldnt be the issue i think.

dont really know where to start with this one

check the arming flags in betaflight, go to the motors tab or just type "status" in the CLI and it'll tell you exactly what's preventing arming. could be a gyro failure flag, could be a failsafe that got triggered and didnt reset properly, could be throttle not at zero when it's reading inputs. the quad just falling like that with no warning sounds like it could have been a brown out or a bad ESC connection ? worth checking your XT60 and the ESC power leads are all solid

3.7v per cell isnt that low but if one cell in the pack is weak it can sag way harder under load than resting voltage shows. ive had a pack read fine on the meter then absolutely crater under throttle and cause a brownout. the FC losing power for even half a second mid flight would explain the sudden drop and might have set some kind of failsafe flag that it's stuck on. plug it in and check the flags like the other reply says, but also id put that battery on a cell checker and do a proper capacity discharge test before flying it again