so i finally got around to fixing my 5inch after i clipped a tree line last weekend and it came down pretty hard on the left rear. snapped the arm partially but not fully through so i figured id just swap the motor and call it a day. replaced it with a spare 2306 i had sitting around, same kv rating, seemed fine.

problem is now when i throttle up past like 40% there's this nasty vibration on that corner, you can see it in the blackbox data and feel it in the frame. props are balanced, checked that twice. the motor spins freely by hand, no scraping, bearings feel ok. im wondering if maybe the arm got some internal damage i cant see? or could the motor screws be bottoming out on the stator or something dumb like that. i dont have another arm to swap in right now so trying to figure out if i can limp it along or if im just going to make it worse flying it.

running betaflight 4.4 if that matters, havent touched the filters yet because i wanted to see what the actual problem was first.

almost certainly the arm. carbon can take a hit and look totally fine on the outside but the fibers inside are delaminated and it just flexes way more than it should. the vibration you're seeing is probably the arm resonating at certain throttle points. you can sometimes feel it if you flex the arm by hand compared to the other arms ? damaged one will feel slightly different, maybe a tiny bit more give to it.

flying it more isnt going to help, youre just going to get garbage video and trash your filters trying to compensate. also wont do the motor bearings any favors. id ground it until you can get a replacement arm, theyre usually like 5-10 bucks depending on the frame.

also check that the motor mount holes on the arm didnt elongate a bit from the impact. ive had that happen where the motor looks tight but its actually got a tiny bit of wobble at the base and thats enough to cause exactly what youre describing. just try to wiggle the motor with your fingers after youve tightened the screws, see if theres any play at all.