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Old 03-16-2012, 03:42 PM   #1
jnissen
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Default Tail wag issue?

I have tried to read up on tail wag issues, but have not managed to get rid of it so far. I sent the following to Jan, and thought about posting it here afterwards so here goes (should probably have done it the other way around but ...):

First of all let me say that I love my TDR, and like it very much already. There are unfortunatley some issues with my heli.


I have some tail wag issue on my TDR (delivered in november) which has been there from the first flying, and I cant seem to get it out of the way. Today I discovered that there is some uneven play on the tail grips, where one can be moved +1mm and the other cant be moved at all. I found a thread at helifreak (http://helifreak.com/showthread.php?t=338587): "How loose is your tail", and the pictures resembles mine very much (the bearings are at different "heights").


I do not think this should give me a tail wag though, and I havent reassembled the tail grips yet (just a few hours since i was out an flew and discovered it).


What happens is that it wags back and fort kind of rythmically for about 6 inches (somewhat depending on headspeed). I have tried different gyro gain in radio and different settings in VBar (Express, so minor adjustments there will amount to setting the endpoints I think).


I have a Futaba 8FG radio, set with Gyro: GY & AVCS, gain at the moment around 30% (ending VBAR at about 80 depending on setting in VBAR), and no matter what I change the gain to it will still wag about the same (somewhat more/less and somewhat faster/slower depending on setting).


I have tried to read up on tail wag issues (in general), but electronical and mechanical and have not found anything I might apply to my setup/build.



I have mainly ruled out electronically issues (I think) and any bindings from the servo to the tailhub, but a few issues mechanically remains.



I do think the tailhub is not running as smooth as my other heli (Trex 550), and have thought about reassemble the entire tail and if necessary try to sand the tail hub somehow with some fine grained sandpaper, and polish it later on. Should that be necessary or a probable cause for the tail wag?


The description in http://www.helifreak.com/showthread.php?t=252719 is about what I have. In the end this issues was that the tail hub was slightly bent and some motor issue (pyro 720 returned to Kontronik).


My configuration is with all mechanical from you, Futaba BLS 452/251, VBAR Express, your rotors, HeliJive 120 and Pyro 720 Black Edition, Futaba R6203SB sbus receiver, and a Futaba 8FG radio.


How probable is it that the tail hub is bent directly from you, or assembled wrongly and bent after flown 5-7 times? Is it possible that the motor might cause a tail wag issue? Can it still be some eletronical issue? Wrong settings somewhere in VBAR or radio?


I would appreciate any input for this issue very much (even pointers if any), but will understand if you do not have the time to spend! Anyway, Thanks in advance!
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Old 03-16-2012, 04:23 PM   #2
abanihani
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Don't have any more experience than you with the TDR but from my humble experience with the logos and other helis, the most likely reason for the tail wag is simply binding of the tail slider on the shaft. this is most likely related to the build, once you put the tail component in place every thing should run as smooth as silk, if not then there is a problem and often times it is very simple but you have to take the tail apart and reassemble it again to find out. my advise is before you start tweeking vbar electronically you have to rule out mechanical issues as electronic tweeking will only make things worse. once everything is working smooth mechanically then vbar tweeking take place. My routine for the tail shaft is to clean first with rubbing alcohol and then I use polished aluminuim magnesium paste and clean with alcohol after that, the slider should go over that as silk and drop fast with gravity when you tilt the tail shaft. after that you have to assemble the tail grips and make sure no binding when you move the tail hub as the slider is moving right and left on the shaft. In the past i had these issues commonly but as i gained more experience building I noticed that I over looked tiny little details in the built that affected flying performance. Touch the wood now i have been having a smooth and successful maiden on every heli i build with only vbar at default setting. Having said that I did not maiden my TDR yet, waiting for the batteries but will post my experience here once it is done. Good luck.
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Old 03-16-2012, 08:34 PM   #3
DT75
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I noticed a significant improvement in tail behaviour after upgrading from 5.0 exp. to 5.2 pro.
Mainly in FFF, but still... + there is the vibration analyzer.
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Last edited by DT75; 03-17-2012 at 06:06 AM..
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Old 03-16-2012, 11:37 PM   #4
Stolla
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doesn't sound right, first check if bearings are seated all the way, also remove thrust bearings and double check so side with smaller id goes towards blades,
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Old 03-17-2012, 01:30 AM   #5
helizen
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i built my tdr few days ago and i have the same tail wag problem..i am using hc3sx but different gain settings have not helped so far..initially there was unequal movement between tail blade grips..one grip was having almost no movement at atll while other had plenty..i used some shims to equalize the movement.. After few test flights the grip that had no movement developed some..i removed the shims that i had added earlier assuming that the bearings did not sit properly earlier..now these grips have similar movement..there is still some minor difference..

The only thing that reduced this tail wag was using some oil in the pushrod supports and tail rotor shaft..i noticed that without this its a little hard to move the pitch slider using pushrod..i also find that the slider moves easily in the central area of the shaft..moving towards the tail hub or blade holders is comparatively difficult..but oiling did reduce this wag significantly..i tried triflow grease but it's sticky and made the situation worse..the wag goes away with high headspeed which is logical..on my logo the pitch slider moves smooth as silk but not on tdr
I have kept this issue aside for the time being as i am struggling with another issue where my servos jump significantly and unexpectedly in a flight..very scary..i have crossed checked everything voltage..carbon fiber detuning etc..i find it has something to do with dsmx and hc unit..nothing clear yet
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Old 03-17-2012, 04:40 AM   #6
shaman3
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During the initial build of my TDR I also had the issue that the pushrod did not move smoothly through the pushrod holders.
It turned I made the mistake of heating the shrink tubing too much (heatgun).
As a result the material kind of swelled. Oiling it only made matters worse, as the oil got kind of sucked in by the tubing material and the pushrod could be merely moved at all after that...
I had to remove the original tubing material and replaced it with some polyolefin one I had in stock. Turned out much better, the pushrod could be moved without any resistance.
So +1 on checking that.
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Old 06-20-2012, 03:06 PM   #7
jnissen
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Default Issue solved (for now!)

I got a psychic knock out kind of from this issue ;-)

I havent event tried to fly since I posted it just getting angry and annoyed at the heli.

Today I finally pulled myself together and managed to start the disassembly of the tail. Called a friend for some support in all regards.

That part went ok, and it seemed like I had all parts assembled right (orderwise!) first time.

When I put put it back together there was some slight change in the one bearing, which now was set as deep as the other was earlier.

Went out in the garden and fired it up and the tail was as good as expected!

In short the bearing was not put all the way in on one side of the tail rotor...

A heating gun is a valueable tool I may say ;-)

The effect of this was that it did bind kind of. At least it did not slide as easy back and forth on the tail output shaft as it should when the one rotor was pulled outwards as much as it is allowed, and the other one was not pulled outwards anything. I would not have guessed that when both are moving outwards those few mm (1-2 possibly at max), it would slide back and forth on the tail shaft easier!

Thanks to all for pointing out the (possible) errors and my own stupidity, not wanting to understand the other thread I refered too.

And a big thanks to my helping (and mainly solving!) hand during this operation!
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Old 06-20-2012, 05:43 PM   #8
jhunter
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I agree with no oiling or greasing of the shrink tube. It swells after a while and makes the matter worse.
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Old 06-20-2012, 08:52 PM   #9
DT75
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A blow dryer do not do the same job as a heat gun...

You could have heated the grips in the oven at 120 deg. C or so, for 15 min. too...

Glad you got it sorted.


BTW : "Location: USA"...?
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Old 06-21-2012, 06:42 AM   #10
Groucho_
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Quote:
Originally Posted by Dumbthumb75 View Post
A blow dryer do not do the same job as a heat gun...
Actually, Someone here had suggested that I use a hairdryer, and I used it for the exact issue of the tail grip bearings not seating all the way in... It worked fine...

I noticed this while building though, not after flying.
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Old 06-21-2012, 07:21 AM   #11
DT75
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Quote:
Originally Posted by Groucho_ View Post
Actually, Someone here had suggested that I use a hairdryer, and I used it for the exact issue of the tail grip bearings not seating all the way in... It worked fine...

I noticed this while building though, not after flying.

Sure, if you have the patience... It did not work for him.

I was referring to his post on a norwegian forum.
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