My racing quad has been experiencing intermittent motor stuttering on motor 3, especially during aggressive maneuvers. Flight controller throws ESC connection errors despite multiple ESC swaps.

A multimeter can be used to measure the resistance of the motor windings and compare it to the normal value to determine if the windings are functioning correctly. Already checked continuity - all three phases show equal resistance around 0.8?.

When hand-spinning, I occasionally feel slight resistance/grinding. Could this be internal bearing degradation or debris? The motor gets noticeably warmer than others during flight.

What's the systematic approach to isolate whether this is motor, ESC, or FC related?

Also, physically spin each of the motors with your hand to listen for any gritty/grinding noises. If you hear this, it could mean there's debris in the bearings. Try compressed air cleaning first, then check if the grinding persists. If it does, bearing replacement is needed.

Had similar symptoms on my 5" build. If the motor still does not spin, the problem is most likely a damaged ESC. But since you've swapped ESCs, focus on the motor. The heat buildup suggests internal damage from the crash - likely time for replacement.

Intermittent issues are the worst to diagnose! It could also be due to problems with the motor windings, such as short circuits or open circuits, which cause uneven magnetic fields during rotation and result in a sticking sensation. Your resistance readings might not catch an intermittent winding fault under load.