Motivation and limitation
I appreciate a good flying Quad and I'm willing to spend some time on the bench to do a clean build and on the computer to get the tune to 90% of what the physical setup is capable off. It took me countless hours to get the hang of it but now I usually spend less than an hour (spread over 2-3 blackbox-analyzing sessions) to get my birds tuned. I don't push my D-terms to the border of oszillation because I wan't to be able to limp them home with a bent or broken prop.
There are very few people that are capable off tuning and willing to tune their multicopters properly and most pilots are happy to throttle through every propwash- and stall-situation because they have no idea how to get rid of it.
PID controller basics
Your flight controller is a small computer that runs (among other things) a routine (PID-loop) that messures the actual state of your Quad, compares it to the state you want it to be (stick input) and sends commands to the ESCs in order to reduce the difference of those two states (setpoint error) as quickly as possible.
Filtering
The gyro-signals on miniquad-FCs are inherently noisy. I have seen BBLogs where over 90% of the gyro signal was garbage. If we would allow the PID-controller to (re)act on the unfiltered data we would either burn out a lot of motors or run PID values so low that our quads would feel increadibly sluggish.
The job of gyro-filtering is to seperate the flight movements of the drone from vibrations that are caused by the spinning props and electrical noise.
PID
P(roportional):
I(ntegral):
D(erivative):
Feed-Forward
Act on the error you expect before it happens
Blackbox M*******r - can you read it?
Unless you are trying to tune out major kinks in your build (see later) you will have a much easier time tuning your rig by analyzing blackbox data. The available tools are excellent and pretty easy to use. I prefere to use Betaflight Blackbox Explorer (download) over PID-Toolbox (download) because I'm able to get a coarse overview/impression of the tune faster.
Both of those utilities will help you to evaluate:
- how your build behaves (noise profile)
- how much filtering is needed
- how good your PID-values represent your Quad