Although advertised as a beginner's guide, the guides were written by someone who does not speak English very well. Even if you need to replace the rotors, there are no instructions on the correct procedure. As a result, I lost the ability to take off after replacing the rotors. As I was about to toss the drone in the trash, I noticed that the box showed the main rotor blades rotated crosswise. I looked at my swap work and realized that I only had one rotor inverter while the opposite angle rotor was aligned with the other three. So I fixed the orientation and that fixed the drone. Keep in mind that NONE of these are documented in the instructions. Also, the controller must have a screw for the battery plate. Mine didn't have any.