title_body: How do you use the PID controller to compensate for a higher weight? How should you adjust the PID values if you add weight to a quadcopter (For example a GoPro), so that the flight characteristics stay as close as possible to how they were before?
  
  I assume that the Feed forward values has to be increased, probably more on the axis with the highest angular mass. But do you have to change for example the I gain as well if the added weight introduces more drifting?
upvoted_answer: I'm afraid there is no simple answer to this question. Adding weight to the quad will change the way it responds so in theory you would need to redo the tune from scratch.
  
  That being said, there are a few assumptions you can make.
  Since the weight goes up, the inertia goes up as well. So it will respond slower to stick movements and will have a bigger tendency to overshoot. To compensate for the slower reaction you can increase the P-gain and/or feedforward. To fight the overshoot (and the effect of the bigger P-gain) you will need to increase the D-gain as well.
  I assume I-gain will not be impacted a lot.