title_body: Kk2.1.6 falling in mid air and losing control I am recently flying my DIY quadcopter built with lightweight aluminum bars and a kk2.1.6.
  
  It was a very good experience until it suddenly started losing control and it fell midair. It tried to gain control as just before hitting the ground and it rose up again for a brief moment before falling again. I also heard vibrations from loose nuts. What might be the reason for this odd behavior?
upvoted_answer: The loose nuts that you hear may be the prop nuts. If this is the case, the props are not held down with enough force and so will be slipping, not providing the torque or the RPM to be able to lift the drone.
  
  I would suggest tightening all of the prop nuts and all of the frame fixings and seeing if the issue persists.