this has been bugging me for weeks now. running a 5" freestyle build, t-motor F40 pro motors, and no matter how tight i get the prop nuts they always seem to work themselves loose after like 10-15 minutes of flying. not loose enough to fly off (yet) but i can feel the vibration come back during rolls and ill land and spin them by hand and yeah, definitely moved.

im using standard m5 prop nuts that came with the motors. running 5149 triblades mostly. ive tried threadlocker on the shaft threads but it made it nearly impossible to change props after a crash so i stopped doing that. a guy at my local field said something about prop nut direction mattering for CW vs CCW motors but honestly i cant remeber which way mine are threaded and the motors dont have great markings.

its not a huge deal safety wise i guess since they havent flown off but the vibes mess with my HD footage and my tune feels off when it happens

the CCW/CW prop nut thing is actually really important and thats almost definitely your issue. the way it works is the prop nuts should self-tighten as the motor spins, so on motors that spin clockwise you want a counter-clockwise threaded nut (so it tightens as the motor spins up). if you have them backwards they'll actively work themselves loose under load which is exactly what youre describing.

look at the bottom of your motor bell or check the t-motor product page for the F40 pro, they usually mark CW and CCW. front-right and rear-left are typically one direction, front-left and rear-right the other. if you have the wrong nuts on you just need to swap them, most motor kits come with both types.

seconding the prop nut direction thing, had the exact same problem and thats what it was for me. also worth checking if your motor shafts are worn or slightly stripped, on older motors ive had the shaft develop a tiny groove that makes it harder to seat the prop properly and it just never locks down right after that.

also ? slightly off topic but since you mentioned HD footage, if youre getting vibes even when props are tight you might want to look at your RPM filter settings in betaflight. sometimes a worn bearing will cause resonance at specific throttle levels and it shows up worse on cam than it feels in the sticks. dynamic notch filters can help mask it but its better to just replace the motor at that point