so i binned my 5inch freestyle quad pretty hard last weekend into a concrete wall, not my finest moment. snapped two props and bent a motor shaft on motor 3. i had a spare emax eco2 2306 laying around so i swapped it in, resoldered everything, looked clean.

problem is now when i spin up all four motors on the bench with no props, motor 3 definitely spins up slower than the rest and sounds slightly different. like a faint grinding almost? i checked the bell and it spins freely by hand, no obvious rubbing. the other motors all ramp up together nicely.

is this just a calibration thing in blheli or is the replacement motor actually damaged too? i checked my solder joints under a loupe and they all look fine. fc logs show the motor 3 output going higher than the others which i guess means the fc is trying to compensate already and that cant be good for long flights.

anyone dealt with this before? wondering if i need to pull the motor back out and check the stator or just toss the spare and order a fresh one

the grinding is your answer honestly. if it spins freely by hand but sounds off under power theres a decent chance the magnets took a hit or there are tiny metal fragments inside from the crash. sometimes debris gets into the bell gap and you dont notice it with a hand spin but once theres any load or speed it shows up. id pull the motor, pop the bell off carefully and just look. also check the shaft isnt slightly bent ? even a tiny bend thats not obvious by eye can cause vibration and uneven spin. a bent shaft will mess with your PIDs something awful too so worth ruling out before you tune around a problem that shouldnt be there

had almost the exact same thing happen with a replacement 2207 i put in after a crash. turned out my solder joints looked fine visually but one of the phase wires had a cold joint that was causing intermittent resistance. i reflowed everything and the motor matched the others. might be worth trying before buying a new one? though honestly if the motor was stored loose in a parts bin for a while it could also just be a slightly dodgy unit from the start, happens