Drone crashed

I have been working on my Quadcopter since last two or three months and i was very happy with the results until i encountered my first crash. Yesterday i went to take a test flight to test the new PIDs that i have gained from autotune. But it crashed within minutes after taking off. I don’t know what went wrong but i am assuming that one of the propeller just came off and it caused the drone to crash. I am attaching the log file below please help. I want to know the exact reason so that i can avoid that before rebuilding my QUAD.2020-10-07 15-36-28.bin (1.6 MB)

Motor 2 lost thrust, Motor 1 was shut down to compensate.

Ohhh. So I was correct. One of the propeller came off and resulted in a crash. Thank you so much mike.