so i clipped a tree branch pretty hard last week with my 5inch freestyle build and ever since one of the motors has been making this weird grinding/rubbing noise when it spins up. its not constant, like it only really comes in around mid throttle and then kind of goes away at full send but that doesnt seem right to me.

ive already checked the props and they look fine, no visible cracks and they spin freely by hand. the motor itself looks okay from outside but i havent pulled the bell off yet. the drone still flies but its definitely pulling slightly to one side and betaflight is compensating a lot on that corner. pid output looks weird on the blackbox log but im not 100% sure what im looking at there.

anyone dealt with this before? wondering if its worth trying to just replace the bearings or if i should just swap the whole motor. the motors are t-motor F40 pro IVs if that matters

had almost exactly this happen with a different motor brand but same situation. the grinding at mid throttle is almost always a bent shaft or a damaged bearing, and honestly with a hard tree hit id just assume both. pulling the bell off will probably show you pretty quickly ? if you see any scoring on the stator or the magnets look chipped you're done, just replace the whole thing.

bearing replacement is technically possible but unless you have the right press tools its more hassle than its worth and you run the risk of damaging the stator trying to get them out. for what F40 pro IVs cost versus your time id just order a new motor. also check your motor screws and the arm itself, ive seen crashes like that crack the arm internally and it looks totally fine on the outside.

the blackbox thing is worth looking at closer tbh. if one motor is working harder than the others to hold attitude that tells you a lot. you can see motor outputs in the blackbox explorer and if that corner is pegged high compared to the others its definitely that motor.

also just curious did you check if any of the motor screws are loose? i had a grinding noise once that turned out to be a screw that had vibrated loose and was just barely touching the bell. felt like an idiot when i found it