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Hello,
Just to add some more data on the stack![]()
The wikipedia article on PID is quiet nice, but PLEASE don't start asking for ziegler nickols methods or things like that, it does NOT apply.
The main thing to understand is that we are not looking for the best response (is there any, anyway ...), but the right feeling.
The PID very basics :
- P(roportional) is the "main gain", it reacts to the error (the error being the difference between the desired speed - stick position - and the real speed sensed by the gyroscope). Too much P gain and the system will oscillate quiet fast, not enough P gain and the overall reaction is sluggish.
- I(ntegral) is the "lock gain", by integrating the error, it allows to not only fight perturbations, but also to come back where it was (without I gain in the wind, you have drift). Too much I gain and you'll get bounce back (caused by integral windup, go check on wikipedia), not enough I gain and you'l get drift or inconsistant rotation speed (piro consistancy).
- D(erivative) gain is the "smoothing gain", it basically "ho shit I'm arriving too fast on the target, time to slow down a bit". Too much D gain and the system will brake too early, not enough D gain and you'll get bounce and hard stops.
- F(eed forward) gain is the "pass through gain", the unit does pass through a ratio of the input - stick position - directly to the servos without even taking care of the gyroscope (by the way you can use the BRAIN on a flybar heli using only feed forward gain on cyclic). Too much F gain and the heli will start very hard and the unit will have to counter the F gain to stabilize speed, not enough F gain and ... well, you'r safe, F gain is mainly about feeling.![]()
- Agility : don't ask, it's one of the secrets of the BRAIN ... Low agility will feel like robotic, more like the beastX, high agility will feel more like a flybar helicopter, with its benefits and losses.
- Stop gain : I guess we will just throw this one away in a futre update![]()
- Tail dynamics : think P3 on BeastX.
- Pitch and Cyclic precompensation : this is why a one axis gyroscope will never be as good as a FBL unit on the tail ... the FBL unit know the pitch and cyclic position at any time, and more pitch/cyclic means more torque to counter, hence the unit can counter it BEFORE the sensor even sensed it (before there is an actual error).
The real problem when tuning a PID (moreover a PID with some ... optimizations), is that each gain is linked to the other, you cannot tune one gain then the others, one by one, if you change one gain, it will have impact on every other gains optimum values.
Start with a default preset, then change (a few % at a time) ONLY one parameter, to feel the difference :
- P will make the heli feel more rigid
- I will make the heli feel more locked
- D will make the heli feel more smooth
- F will make the heli feel more aggressive
- Agility will make the heli feel more natural (more robotic is you decrease it)
- Tail dynamics will help to prevent gear stripping (lowering it)
- Asymmetry will help get same speed and reaction on both tail directions
- Pitch/Cyclic precomp will make the tail not deviate when doing hard climbouts and fast rolls/flips.
Hope this helps.
Thomas.