What is the Difference between ATC_RAT_RLL_FF and ATC_RAT_RLL_VFF

ArduCopter Traditional Helicopter
1

Hello,

I would like to tune _FF for roll and pitch.
Which parameter do I control with the Tuning button when I enter the value 53 (= Rate Roll FF) there.

Do I change with it the value ATC_RAT_RLL_VFF or the
value ATC_RAT_RLL_FF?

What is the difference of the two parameters?
Is the parameter ATC_RAT_RLL_FF used at all for the traditional heli?

Thanks for a short clarification

Heri

1 Like
2

@heri they are the same. Multicopter changed it to FF and heli left it as VFF.
I don’t think you need to use the tune knob to adjust VFF gain. This is best done looking at data. I know there are probably other threads where I have discussed how to determine VFF. For pitch and roll axes, basically it come down to increasing it until the actual rate matches the desired rate using the log data. Actual roll rate is RATE.R and desired roll rate is RATE.Rdes. Actual pitch rate is RATE.P and desired pitch rate is RATE.Pdes. You should also see the p term in the PID log data reverse during the response. So as the requested rate is still going in one direction, the p term will at some point go in the opposite direction.

Hopefully that makes sense

3

look at the graph in this post of mine.

See how the P term makes a wave or sinusoid like shape where it initially goes in the direction of the input and then reverses.

4

Bill, thank you for your help. I will study the linked thread.

BR

Heri