tail twitching on rainbow ends (solved)

Hi,

This is my setup:
- Atom 500 with stock motor (1050Kv). 10T pinion, 78T Main gear.
- Silverline VBAR 5.3.4 pro
- Align DS510M cyclic
- Hyperion DS20xGCD tail
- YGE 90 LV v3 (Mikado version). Set for vbar governor mode.
- Hitec Aurora 9 radio with Optima 6 receiver.
- RPM set to 2650.

First I had my tail servo ball at 13mm (as per the heli manual) with tail endpoints at 100(CCW), 100 (CW) but it was giving me a slow wag during hover.
Changing gains didn't fix it. I moved the servo horn one ball in to 10mm with tail endpoints at 130 (CCW), 130 (CW) and the slow wag was gone.

For tail gain tuning, I set governor gain to 10. Set the tail P/I gains to 75 and tail precomp to 10 (collective), 3 (cyclic). Tuned the common tail gain till I no longer had wag in fast forward flight. Hurricanes are also nice with no wag.

Then I started to increase governor gain. At governor gain 20 I see "Raised vibration levels" in the log every 10 seconds. At governor gain 15 I don't see them.
Is this normal or something wrong with my drive train?
I've attached the vbar log. In the log, flight with gov gain 15 starts at pg. 26. Flight with gov gain 20 starts at pg. 29.

Another issue which bothers me more is that I see tail twitching during transition portion (ends) of rainbows. How do I dial that out?
Do I increase tail precomp or do I increase 'I' gain? Could governor gain be the cause? I've tried 5, 10, 15 and 20 and none of them fixed the issue.

I have my tail static pitch set to hold straight during rate mode. Torque precomp Zero Collective is spot on. Vbar setup file is attached as well.

Thanks in advance

regards,
Roger.



Edited 2 time(s). Last edit at 10/08/2016 06:18PM by stark.

Vibration entries during a flight are normal (blades etc.) as long as there is no issue like drift etc. - they depend on your flying.

Quote:

Another issue which bothers me more is that I see tail twitching during transition portion (ends) of rainbows. How do I dial that out?

Please check your stick calibration:

- setup collective panel
- fold blades
- move stick unless tips are on equal height
- fold back
- flight tail panel
- click "set"

Value?

regards (EN) / Gruss (DE)

Rainer Vetter

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Hello Rainer,

Thanks for the quick response.

I got a value of -3 for zero collective position.

regards,
Roger.



Edited 1 time(s). Last edit at 09/18/2016 10:17PM by stark.

Thats not too far off.

Can you please tell - in the time of the collective input - does the tail twitch CW or CCW?

regards (EN) / Gruss (DE)

Rainer Vetter

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I wasn't sure so I went to the field again to check. This time I flew with -3 collective zero and gov. gain of 15.

The twitching was still there. It looks like a fast oscillation (2 Hz) with a small amplitude. The heli seems to move in both directions CW and CCW about 2 times before settling in.
It is hard to tell which way it moves first but looks like it is CW first.

OK - so i would try to decrease the torque precomp on collective a bit ;-)

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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Reducing the collective torque precomp didn't help.

Instead, I tried increasing the collective torque precomp to 40 and reducing common gain to 60 and I gain to 50.
It got a lot better with this but still not perfect.

I'm not sure if the governor mode is causing this or something wrong with heli setup. To figure this out it would be nice to verify with governor mode disabled.
Is it possible to disable governor mode? e.g. in governor tab, Banked (expert) mode, option set to "throttle curve only"?
As I have only 6 channel receiver, I can set "preset channel from receiver" to fixed and "throttle input from receiver" to AUX and set the throttle curve in the transmitter radio.

By the way what does "fixed" mean? How to set the RPM setpoint when preset channel is fixed? It probably doesn't matter in "throttle curve only" mode but I wanted to get an understanding of it.

Fixed means - the max RPM is taken as RPM in this bank.

Disable gov - easy - just select "external gov" and set up from TX ;-)

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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Quote:

Disable gov - easy - just select "external gov" and set up from TX ;-)

I couldn't find "external gov" anywhere in Vstabi setup utility. Note that I'm using "separate channels, standard RX hookup".

Or did you mean in Electric Governor, use -100 to 0 in AUX channel in transmitter to keep gov off?



Edited 1 time(s). Last edit at 09/20/2016 08:00PM by stark.

OK. Since I'm using standard RX hookup, I cannot provide "Throttle" channel to the VBAR. Only "Preset" channel via AUX port. This limits me so that I can't use throttle curve from transmitter in Electric governor mode when preset channel is less than 50%.

Or did I miss something?

I think only available option is to use "Expert governor", Select "throttlecurve only", select "preset" channel as Fixed, and "throttle" channel as AUX (CH5) and set throttle curve in transmitter.

What about connecting ESC master direct to RX Throttle for a test?

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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Edited 1 time(s). Last edit at 09/20/2016 10:07PM by RV.

Tried with governor disabled today. I didn't want to change wiring so I used the "Expert governor" "throttle only" with throttle curve in TX.
I had set tail collective & cyclic precomp to 0.
Headspeed was also around 2600~2700.

With a V throttle curve I can still see the wag during disc unload/load just like in governor mode.
If I use a flat throttle curve then it is reduced a lot but still there. The slight twitch could be due to headspeed drop. Probably it could be dialled out with milder v curve and proper tail tuning. But no governor is not my target so I won't spend more time in this path .

I'm suspecting that my tail servo is not a good match. Could very low servo dead-band be the cause? The Hyperion DS20 series seems to have a default dead band of 2uS. Would that explain why the slow wag in hover went away with moving the tail servo ball one position in?
http://www.rotory.com/fusionbb/showtopic.php?tid/76849/
I have ordered a Savox SH-1290MG for the tail. When it arrives I will test it and report how it goes.

Meanwhile is there something else I should try?
My current motor pinion is 10T with 78T main gear. My desired governed headspeed is 2600RPM. Motor is 1050Kv with 6S setup.
Should I drop the pinion to 9T to reduce tail kick on motor throttle?
The motor is quite powerful and I have very good SLS Lipos so I'm guessing the tail just can't keep up with the motor torque.

Can tail belt tension be ruled out. My tail belt is just perfect. Not loose or too tight.

Should I suspect the One-way bearing? At least on bench it seems to be smooth.

regards,
Roger.



Edited 1 time(s). Last edit at 09/21/2016 05:12PM by stark.

OK. It's been a while but i've not been idle. I've been chasing my tail the whole time.

So, tried a brand new tail servo Savox 1290MG. No improvement.
Put on a new tail belt and kept it tighter than before. Still no luck.

I decided to observe the heli more closely as to what was happening.
During pitch pumps, in negative to positive collective transitions with heli upright, not only the tail was kicking right but the heli was shaking on other axes as well.

On checking the head for any issues I found out that the swash servo mounting was not tight enough.
I beleive it was loose enough to move on heavy load on the main rotor disc.

After fixing this and moving the tail servo arm ball from 10mm to 13mm the heli shake was gone.
Tail precomp was reduced to 15/5 as well.

I didn't spend much time fine tuning the tail after that but I'm already quite happy that the shake & kick issue is gone.

Now for fine tuning the tail. Is it better to have lesser tail precomp and higher I gain or lower I gain and higher precomp?
Which parameter should I tune first?
1) First tune tail precomp with low common tail gain and doing mild pitch pumps.
OR
2) Keep tail precomp 0 and tune as high tail common gain and I gain as possible then add precomp.

Thanks for the support .

Hi,

precomp is kind of a static add, so I would first dial down overall gain a little and set precomp (climb outs for collective, stationary flips and rolls for cyclic), then dial in overall gain again.

With precomp set properly, the control loop is pretty much unloaded even in full collective climb outs or full deflection rolls/flips, and can concentrate on the finer work.

I would not touch I and P gain if I get it right with precomp and gain, the default values and the ratio are pretty good empiric default parameters which work on most helis pretty well.

Best,

Eddi

Born to fly ...
forced to work.

Hi, what did you end up doing to fix this issue? i am experiencing the same thing on both helis. Dead on.

Keep the board clean.

One Heli, One user, One thread.

Please open a own one and add more infos about the heli, equipment, setup file.

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.