Minor crash, no visible damage, props not broken. Now when I take off, one of these happes. Either a) One motor won't start and I see an error "motor obstruction", or b) One motor won't start but the drone will try take off and immediately tip over and crash again. If it does not crash, it shuts down and will not attempt a spin up again unless I power cycle the drone. All motors spin freely and I don't see any debris or physical indicator that the bad motor is damaged. I took the lid off - I don't see anything obvious, but I don't know what to be looking for other than something broken or dislodged. Please help on how I could fix this myself if possible. I'm an electrical engineer, so I'm comfortable doing surgery.