Manual tuning FF formula in the wiki don't make sense

ArduPlane Plane Simulation
1

Hi! New guy here, so hope this is the correct place to ask…

Been reading the page regarding manual tuning :

https://ardupilot.org/plane/docs/new-roll-and-pitch-tuning.html

It suggest finding FF (pitch for example) using the following graph:

(proposed FF) x PIDP.Act x AETR.SS

And comparing it to AETR.Ele x 0.01.

In my understanding, the action of the FF path in the controller is from PIDP.Tar, so the graph should be

(proposed FF) x PIDP.Tar x AETR.SS

What am i missing?

Thanks!

2

Hi B12V,

(proposed FF) x PIDP.Tar is used in the controller to calculate what position the elevator should be set to (AETR.Ele), but there is no guarantee that this will produce the pitch rate PIDP.Act equal to the target PIDP.Tar, since the FF gain may not be tuned properly.

We know that in flight, the actual elevator deflection (AETR.Ele) produces the actual pitch rate (PIDP.Act), and the ratio between these two is what the pitch FF gain should be.

So, the FF gain can be determined by plotting (proposed FF) x PIDP.Act x AETR.SS and comparing to AETR.Ele x 0.01, and then trying different values of the proposed FF until the graphs align. This is best done during sections of flight when the demanded pitch rate is high.

Hope I could shed some more light on this…

3

Ok, i understand my mistake now

I thought PIDP.Act is the out of the PIDP (as in “action”) and not the signal (“actual”)

That makes alot more sense :laughing:

Thanks!