Tuning - Getting Started

I'm new to V-Bar (& FBL) - but not to helis (or control theory...)

I've put together a T-Rex 450 Pro with 5.1 Pro. I'm confident that the set-up is reasonable. The heli flies reasonably well, but needs tuning.

Is there a tuning guide ?

With a conventional gyro, I'd increase the gain up to oscillation; then back off. This doesn't seem to work with V-Bar, as oscillation never occurrs - making me think I'm barking up the wrong tree.

Auto-Tune is for fine tuning ? (Doesn't seem to adjust major parameters ?)

Anyway, I'm looking for a guide to initial tuning, etc.

You may find some tips for cyclic here:

http://www.vstabi.info/en/node/399


And tail here:

http://www.vstabi.info/en/node/1057


About the gain ... on tail you may see some oscillation but on main rotor it will be nearly always save ;-) - I use 60....80 gain on 450 size.

regards (EN) / Gruss (DE)

Rainer Vetter

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Thanks.

My game plan was broadly to start with the 450 defaults (but with both main gains backed off slightly to be on the safe side); then up the tail gain (as with a regular tail gyro); then do similar with the swash gain. Then I could consider playing with the more advanced parameters, or rate/style/etc.

Given that I now have a flyable heli, I think I'd like to look at the tail first.

So, from what you're saying, it seems the tail optimizer acts only on the two 'Control Loop' values; and that these are used as predictive hints.

I think I'll leave these as the defaults for now, and run the optimizer when I have the other tail values more sorted.

Similarly, the 'stop gains' sound like fine tuning for later.

Let's see if I've got the right idea with the fundamentals...

The yaw gyro measures the heli's actual yaw rate (degrees/s etc).

The rudder stick, in conjunction with the yaw rate parameter, sets a yaw demand. This is compared with the actual yaw rate to give an error value.

The tail pitch is a function of:

@ error * proportional gain [matches yaw rate to demand]

@ Integral of error * integral gain [matches integrals of rate, ie heading hold]

@ & the clever optimisations, including collective & cyclic compensation.

Are all of these scaled by the main 'Tail gain', or are only proportional & integral scaled ?

So, I'd guess I want to initially play with the main tail gain, proportional & integral to get a good tail hold without a fast or slow wag ?

Only P and I are scaled with the gain.

About the 450 tail in general .. which servo do you use?

regards (EN) / Gruss (DE)

Rainer Vetter

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Posting and answering - please use a PC and a standard keyboard. Answer all questions fully, take the needed time, don't forget probably requested attachments.

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RV Wrote:
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> Only P and I are scaled with the gain.

Thanks.

> About the 450 tail in general .. which servo do you use?

It's an S9257.

[This tail and servo were pulled straight off another T-Rex 450 Pro, which was flybarred, and had a Spartan DS760 driving the tail. This configuration behaved well. Having said that, there some mechanical issues for me to look at. I need to look at the 'zero' pitch, and the tail thrust bearings have been coming apart (!). So I need to get this sorted before going tuning...]

Another question. Does the effective servo horn length interact with the gain values - or does it come out in the wash when you set the servo end-points ?

9257 is pretty god, our recommendation for 450.

With more length it can be like a gain boost - if the servo has enough force -

We adjust the length to get throws around 100 for best results.

regards (EN) / Gruss (DE)

Rainer Vetter

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Posting and answering - please use a PC and a standard keyboard. Answer all questions fully, take the needed time, don't forget probably requested attachments.

Für Posts und Antworten bitte einen PC und eine richtige Taststaur benutzen sowie alle Fragen vollständig abarbeiten. Nehmt Euch Zeit, beantwortet Rückfragen in Ruhe und vollständig.
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Für Einzelkommunikation bitte ausschließlich Email verwenden! - PN, Messenger, Chat usw. werden nicht bearbeitet.
For single user communication please send a email only! PM, Messenger, Chat etc. won't be read.

Cheers.

The mechanical issues have now been improved. Increasing both P & I gains by 10 let me set a gyro gain that made the tail oscillate under duress, and then back off until this didn't happen. Which made me happy, and the tail seemed pretty good afterwards.

So, I definitely feel I've got started...