hi guys. today i was flying over a gravel path and when landing the quad flipped and ended upside down (motors facing down), i turned off motors did a quick inspection and didn't notice anything unusual, however when i turned motors again one of them didn't started and i noticed a tiny rock (gravel) was stuck inside the motor. i tried to manually spin the motor and i found it difficult, however i turned on again the motor and it worked (i flied for about 20 more minutes). i know the tiny rock is still inside the motor, so my question is: should I worry about the rock? is there any chance that once the motor is spinning the rock causes it to stop with fatal consequences? thanks for your help.