Solved! Strange tail problem

I am having problems with tail drift on my Urukay Carbon. This becomes very visable in the hovering manouvers where i fly with 1400Hs and 1450Hs. The tail holds good in the wind and stops are good, but the tail drifts when i descent and apply positive collective pitch. The drift is relatively slow, but i can easily get a 90degree drift after 4-5 descends like the ones in the "flower" and "cup" hover manouvers. The pitch range is very limited and almost flat in the hover range, total pitch is about -2 to + 6 degrees.

The heli is set up with 105mm tail blades (2 bladed setup) and 1:5,297 tail ratio. There`s a MKS 990HBL tail servo, and both the servo arm and control arm on the tail is at 90degrees. I have tried all i can think of to fix the problem. Every tail gain, collective precomp, P and I gain, setting zero, adjusting linkage length, manually adjusting trim, autotrim, leaving optimizer on, 115mm blades. Nothing helps.

My friend uses a similar setup, but has a 3 bladed tail setup at 100 gain. His tail experiences none of this.

Help!



Edited 1 time(s). Last edit at 01/13/2019 08:52PM by Runarsk.

Well - is it only on this particular heli or on others with the same radio/pilot too? (to check out if it is a radio/poti issue or the pilot moves a little bit tail while giving collective, last could be easily proved when adding more Expo)

Which VBar is it and which Radio?
Could you add a setup file?

regards (EN) / Gruss (DE)

Rainer Vetter

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Good morning Rainer

This is only a problem with this heli and on low HS. At 1850HS the drift is gone. I'm pretty sure I'm not giving any input as expo is in the 70-80 range and agility is at 50. You really have to move the stick to see any rudder.

This is a new Neo vlink and VBC v1 (please send my new Touch asap haha)

I'll post setup file when i get home.



Edited 1 time(s). Last edit at 06/27/2018 10:37AM by Runarsk.

Hi again

The setup file is attached. In bank 2 you can see that i have done some tweaking on P and I gain in the tail parameters.

Hello,

there is no hint in the file ;-(

but - you may try some D part, start with a amount of 5 or 10 - be careful at tail stops, if it oscillates dial down a few points.

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.

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Seems I can set PID gains pretty high without any problems.

I've lowered acceleration from 55 to 30 and this seems to help but I can't quite figure out the logic.

Hi,

lowering acceleration (which can be compared to delay, on vintage gyros) adapts the time constant, which helps with heavier and more inert birds like our 800 XX or scale models, with their comparatively weak tails or general slower response. I think it's coincidence, on your bird.

You have very particular collective curves, and our DMA (tail precompensation) works like a V shaped curve from zero collective, adding anticipatory tail thrust, for the expected change in torque. Which isn't there, of course. So the precomensation probably moves the tail and is being fought by the gyro.

I would recommend a) setting zero collective in bank 1 and two, in the tail rotor expert panel (stick to the zero collective position (which is not center in bank 1 and 2) and click) and b) reduce DMA Collective and DMA Cyclic considerably or maybe even zero it out , in the hovering bank(s).

Kind regards

Eddi

Born to fly ...
forced to work.

I've tried your recommendation today but the tail is still drifting. I'm going to try a smaller pulley to get more tail speed.

Are you saying that I should change my pitch curve and have zero pitch closer to the center of the curve? The reason for the curve is to have a very calm collective feel in hover maneuvers.

Hi,

in general, it doesn't matter how your pitch curve looks like and where the center (0°) is. Just for the tail precompensation, it's important the VBar 'knows' if it's off stick center, so it can calculate it's V shaped curve from there. Or, as being said, you zero out the precompensation, in calm collective maneuvers it's not really required after all.

Could still be that the radio is outputting a very small signal which is just above the stick dead zone, though.

Can you monitor this drift on the bench, with the motor running (without blades)? If so, you could swap e.g. aileron and elevator channels and try again, so a different gimbal/potentiometer is in the loop for the tail. All on the bench only, of course.

Honestly I don't think it's a tail speed (or thrust, load) issue.

What you could also try is manually add some auto trim value to the tail, just to check.
Or add the smallest trim value to the tail stick (VBar needs to be initialized before doing that, else it would learn the slight offset as center).

Kind regards

Eddi

Born to fly ...
forced to work.

I will do some research based on this. My Touch is being delivered on Wednesday so any potential problems with my current Vbc would be solved.

First flight with new Touch didn't resolve the problem so no gimbal problem. I've also tried manually setting the tail trim against the torque but this has no effect.

Could it be the Neo?

Hi again,

does it do the same if you have a conventional collective curve, with zero collective at center stick?

I do not know what of my ideas you did try yet ...

I doubt it's the NEO, hardly any issues with the sensors since it has been released.
Simplest thing to do would be to mount a different one, for a cross check.

But I would not want to rule it out completely, it's just that if the cause was within the rather particular setup, we would only spend time and money on sending the NEO in, while a couple of productive tests could help shedding light on the thing.

Kind regards

Eddi

Born to fly ...
forced to work.

I'm at the field, so I just tried a conventional collective curve. No change there either. The drift is also present at 1800hs.

What I've tried so far:
Resetting collective zero in menu
Setting DMA to zero
New trim flights
Setting trim manually
Trying a new VBC
Checking for vibrations, none on the touch analyzer
Setting up tail from scratch, perfect 110-110 in setup with 2-3° against torque
Gain all the way up
P and I very high
D higher

Hi,

OK, this more or less only leaves the VBar, although it's rather unlikely. Sherlock Holmes might be right again, I guess you know the famous quote.

Do you happen to have a second NEO, for a cross check?

Please open a service request for this unit, I can also see that we can send a replacement, for the cross check.

Kind regards

Eddi

Born to fly ...
forced to work.

I have other Neos I can try, but thank you for your offer.

Can I just save the model setup and import to the other Neo without doing any more setup?

Hi,

yes, you can. Just make sure that a virgin NEO has at least once a setup made from either the PC Software or VBar Control (Create new Setup, click all the way through the wizard, just to make sure all factory parameters have been set).
Else, the servo's would not be enabled, even if you load a full setup from a different VBar.

Kind regards

Eddi

Born to fly ...
forced to work.

Ok now I'm just confused..

I swapped the Neo from my Logo 800 but the tail still drifts. I can't see a mechanical reason, many I should try another servo?

Hi,

I would first start over with a new, generic setup. Only as much as you need to fly the machine, nothing fancy.
Maybe there's something in the file we do not see.

In hovering, a servo should not make a huge difference, but of course that would also be an option.

Cheers

Eddi

Born to fly ...
forced to work.

I'll do a new setup as you say and report back.

Hi!

Did a New setup from scratch with no luck.
Changed to a new tail servo and made sure values are good.
Built a completely new tail
Changed the servos from older Aligns to new Mks 960.

Tail still drifts slowly ccw

Hi,

I'm quite lost I must say. Since two VBars show the same, but the one from the 800 did obviously not, on the 800, it more or less must be something on the model.

Can you please post the current setup where you still/again have the drift?

Cheers

Eddi

Born to fly ...
forced to work.

Well there`s not much else to swap out. The remaing electrics are one Kosmik 160 and a R2 Buffer Pack.

Attached is the latest setup i flew with 8 times last thursday. Everything works perfect except the tail.

What about the motor causing microvibrations?

Is it visible on the bench w/o blades?

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.

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I'm heading out to the field later so will check. Would those kind of vibrations be visible on the vibration analyzer?

Depending on their Frequency they may be above the measuring Range of the sensor.

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.
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Just tried spooling up on the bench without blades in all three HS 1400, 1450 and 1850 but couldn't see any sign of drift. There is virtually no vibrations in the analyzer at all, the value is 20-40 in the lower head speeds. The same when hovering.

One question - is the NEO used with a external sensor? (if yes - unplug it)

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.
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No external sensor.

Do you think this is caused by something mechanical? I'll try to get ahold of a different motor and check.

Hi again,

I still think, if two different VBars show the same effect on the model, it's not the VBar(s) but something else.
And if it doesn't happen with different models, it's most probably not the radio.
This more or less only leaves the model, the other electrics/electronics thereon, and the mechanics.

Kind regards

Eddi

Born to fly ...
forced to work.

I just flew a battery with a brand new motor and the drift is still there.

What I`ve done so far:
2 Neos
2 VBC
2 tail servos
2 motors
2 swash servo combos
Changing all the parameters described above
Checking vibration analyzer, see pics for screenshots

The things I havent tried:
Different wiring from Kosmik to Neo, they are bundled togeher now, both leads have ferrite rings.
Moving Telme away from motor wires
Another Kosmik
Changing every rotating part on the heli

Guess I`ll have to start in that order?