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Rudder flutter problem...

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Old 08-17-2010, 01:15 AM
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mc15601
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Default Rudder flutter problem...

I am pretty sure that the flutter in the video isn't supposed to happen but I'm not sure what is causing it or how to correct it?? It happens with both small movements, large movements, as well as, letting it snap back to neutral. I thought maybe it was the position of the control horn, but it looks aligned with the rudder hinge. This plane is a .61 Reactor Bipe, and the servo is Futaba S9650 (digital).

Anyone have any idea's?

[youtube]http://www.youtube.com/watch?v=ZkyBYSg_U58[/youtube]

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Old 08-17-2010, 06:00 AM
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da Rock
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Default RE: Rudder flutter problem...

Ideas?

Yes, swap out the servo and see what another one does. Older servos would do that when they needed cleaning.
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Old 08-17-2010, 06:23 AM
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Augie11
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Default RE: Rudder flutter problem...


ORIGINAL: da Rock

Ideas?

Yes, swap out the servo and see what another one does. Older servos would do that when they needed cleaning.
Yes, definitely check the servo. And make sure there is no 'slop' in the linkage and, if you're using a servo extension, try another one.
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Old 08-17-2010, 07:21 AM
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Dr1Driver
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Default RE: Rudder flutter problem...

Yup, looks like a dirty or worn out servo to me, too. They're usually not worth trying to clean and you'll probably never get all the dirt out. Scrap it.
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Old 08-17-2010, 07:24 AM
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vasek
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Default RE: Rudder flutter problem...

if swapping the servo don't help, from what i can see in your vid it could be the rudder is not rigid enough thus it's flexing/vibrating by itself(?)
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Old 08-17-2010, 10:19 AM
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mc15601
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Default RE: Rudder flutter problem...

The servo is brand new, just installed.  But I will try to swap it out with another when I get chance tonight.

Thanks for the replies!

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Old 08-17-2010, 10:24 AM
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mc15601
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Default RE: Rudder flutter problem...


ORIGINAL: vasek

if swapping the servo don't help, from what i can see in your vid it could be the rudder is not rigid enough thus it's flexing/vibrating by itself(?)
I don't think it has to do with the rudder not being rigid enough, although I can see why you would think that because the video gives you that illusion that it is flexing but it really is not.
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Old 08-17-2010, 10:49 AM
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Default RE: Rudder flutter problem...

If another servo doesn't cure it then having a bad or dirty servo lead can do the same thing. One thing at a time, change the servo then the lead to be sure what the problem was/is.
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Old 08-17-2010, 10:53 AM
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Default RE: Rudder flutter problem...

To me it sounds like you are letting the stick just snap back to center on the TX...

if this is the case then the servo is doing exactly what it is being commanded to do.
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Old 08-17-2010, 10:58 AM
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Default RE: Rudder flutter problem...

I bet a fully charged high voltage pack with enough slop that the servo is over centering. Happens with digital servos. I bet it does not do it with a pack that has been drained a bit like a flight's worth.
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Old 08-17-2010, 12:00 PM
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Default RE: Rudder flutter problem...

Hi!
Probably a bad potentiometer! Seen this many times during my 36 year in R/C flying. It's easy to fix! Just open up the pot and tighten the viper pot arm!
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Old 08-17-2010, 12:13 PM
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Rodney
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Default RE: Rudder flutter problem...

First off, this is not flutter, at least not in convention definition of flutter. Instead it is an oscillation which can be caused by several factors. The more probable in this case is a slightly sticky push rod that has a lot of friction to movement near the center position. It could also be caused by the rudder hinges not being in perfect alignment causing them to be at rest in the not-quite-neutral position and wanting to snap to a slightly off set position an neutral. It could also be a dirty potentiometer in the servo itself or a well worn one. If it is the servo, you should be able to see the servo jitter when the rudder push rod is disconnected from the servo. If, with the rudder push rod disconnected from the servo, the servo does not jitter then it has to be friction in either the push rod or hinges on the rudder and the servo has a clean bill of health.
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Old 08-17-2010, 02:55 PM
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Default RE: Rudder flutter problem...

Bad servo, or lead, but more than likely servo. Send it to Hobby Services and you will get a new one back.

David
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Old 08-17-2010, 03:40 PM
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Default RE: Rudder flutter problem...

I agree with Rodney; that is not flutter.

The amplitude of the oscillation shown in the video gets smaller with time, instead of bigger or reinforced by the airstream.

It is just like a deflected spring that is liberated.
The reason is the same as for the spring: elasticity of the whole system formed by servo, linkage, horn, hinge and control surface.
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Old 08-17-2010, 05:20 PM
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Default RE: Rudder flutter problem...

I just checked on the Futaba site...the S9650 servo is only recommended on electric powered cars......where a servo searching for center such as yours is, is no biggie.
You have the wrong servo..and it seems a little weak for rudder
Good luck
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Old 08-17-2010, 05:54 PM
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Default RE: Rudder flutter problem...

am I the only one that hears the flicking of sticks in the background.......??
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Old 08-17-2010, 07:27 PM
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Default RE: Rudder flutter problem...


ORIGINAL: exeter_acres

am I the only one that hears the flicking of sticks in the background.......??
No. But that is just one of the other reasons, may as well have a good list to look at.
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Old 08-17-2010, 08:46 PM
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Default RE: Rudder flutter problem...

Problem solved. Was a combination of a couple of things. First, I repositioned the linkage on the servo arm and control horn (I think this was the biggest problem), then I made sure there wasn't any slop in the linkage. Problem gone!

Thanks for everybody's help.
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Old 08-17-2010, 11:53 PM
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Default RE: Rudder flutter problem...

The easiest fix is usually the correct one on new equiptment.
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Old 08-18-2010, 07:49 AM
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Default RE: Rudder flutter problem...

I had this happen last year with a new digital servo on the rudder of a Venus II. It went away when I reduced the rudder throw by moving the clevis to the outside hole on the rudder horn.
I believe it's caused by a combination of a heavy rudder (lots of inertia) and the narrow deadband of digital servos. The rudder overshoots neutral because it's so heavy, the servo corrects, the surface overshoots and the whole process repeats itself.

After I reduced the throw I flew the whole season without any problems.
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Old 08-18-2010, 09:15 AM
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Default RE: Rudder flutter problem...

Common problem nowadays with digital seros and any large control surface.
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Old 08-18-2010, 05:12 PM
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mc15601
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Default RE: Rudder flutter problem...


ORIGINAL: j.duncker

Common problem nowadays with digital seros and any large control surface.
Yeah, I'm starting to realize this after being away from the hobby for awhile now. It's taken some getting used to the noise the digital servos make. You would think with the advancement of technology, and them being digital and all, they would be quieter than their predecessors. This is my first experience with digital servos and when I first tried them I thought the gears were already stripped!! lol But the noise will be drowned out by the motor so I'm not complaining, so long as they keep the plane in the air
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