If the Quadcopter is a MIMO Nonlinear System, How Can it be Controlled using PID? I know that it is very common to control quadcopters using PID algorithms. I'm just wondering if it isn't a problem that the system is highly nonlinear as well as having multiple inputs and outputs. Does the model need to be linearized so that PID algorithms can be used?

Thanks in advance!
If the Quadcopter is a MIMO Nonlinear System, How Can it be Controlled using PID?


Exactly as you mention later:


  Does the model need to be linearized so that PID algorithms can be used?


Yes, that's correct.

To be a little more explicit, you need two things:


linearise the system (usually around a so-called "working point", e.g. cruise conditions)
de-couple the system (because a linearised MIMO is still a MIMO, you need a set of 4 SISOs)


Achieving the first is fairly simple, as I mentioned, you "only" have to select a working point. The second is instead a little more elaborate, and requires making assumptions on the flight conditions that will be encountered, plus it is not always possible, some vehicles have their dynamics so coupled that de-coupling is not an option (and thus simple PIDs tend to be not a viable option if you have to tune them manually).