Is it a software bug?

[lehar]

SW version: MultiWii 2.2
I think there's a bug in multiwii.ino

PTermACC = constrain(PTermACC,-conf.D8[PIDLEVEL]*5,+conf.D8[PIDLEVEL]*5);
I think it should be:
PTermACC = constrain(PTermACC,-conf.P8[PIDLEVEL]*5,+conf.P8[PIDLEVEL]*5);

[Sebbi]

Short answer:
no

Long answer:
A PID controller has a proportional term (P), an integral term (I) and a derivative term (D). MultWii uses a full PID controller for gyro based corrections, but only a PI controller for accelerometer based corrections. The D value is instead used to limit the influence of the accelerometer ... the D term is generally not used when the signal source is noisy and leads to jumps.

[alll]

... the D term is generally not used when the signal source is noisy and leads to jumps.

worth reading...
http://wearcam.org/absement/Derivatives ... cement.htm

[lehar]

okay, is there a document or a short description, how each PID works? (differs from a standard PID controller, etc. use D as some other than D parm)

[alll]

You are dreaming, some will say "it's all in the code"..., to my knowledge there is not (yet)

[rbirdie001]

Hi!
I don't want to open new thread for my obsevations when there is similar topic .
I think I may have a found bug in the MWI 2.2 code and it seems to be present even in next developement versions. It is in accelerometer I term influence in default "tradional" PID loop (option 1) in HORIZON and ANGLE modes. In short the I term of Accelerometer PI loop have incorrect influence while P term works as it should. See ilustration videos:
At first video is tricopter lying on the ground and tail is supported by a brick so ROLL axis is levelled and PITCH axis is tilted to front. It has loaded stock MWI 2.2 withou any modification.
In acro mode all motors are running equally because no movement so no gyro corrections.
In the first part I adjusted just P term for the LEVEL, I term was 0. When I activated (at 0:07) HORIZON, front motors speeded up and rear motor slowed down because P term tries to compensate tilt on PITCH but both front motors are still have the same speed (because ROLL is levelled). That's OK.
Then I adjusted I term constant to 0.069 which is more than default but still reasonable value and again activated HORIZON mode (0:28 and again 0:42).
You can see that motors first did the same as before but very fast right motor started speed up more than left one so it looks like that I correction to PITCH is incorrect because this shouldn't affect left/right motor balacing. Hear "narrator"

http://www.youtube.com/watch?v=z2rAY_X_u3w

For complete image I repeated tests with a quad in angle mode and for both axis - again I'm afraid that results is, that something is strange.
No narration here, but see the cursor. Always one axis is levelled and one is tilted. When only P term is applied, there is correct influence of ANGLE mode but after applying I term there is a strange behaviour.

http://www.youtube.com/watch?v=HOAfjeJoBiY

I did short tests with the newer PID algoritm (option 2) and it seems to work fine.
Because I'm not experienced in code, I hope that someone from programmers can look at it and possibly correct it or correct me .
Thanks!
Roman