stronger control rod

I have my elevator servo mounted externally in the tail useing a 4-40 rod linkage. At idle on the ground the rod vibrates causing it to bow about
1/4" to each side. This makes the elevator flutter. I'm assuming once the plane takes off the flutter goes away because the plane seems to fly just fine. But what I'm worried about is damage to the elevator servo causing a failure in flight. The rod is about 6" long, is there something better that I could use which wouldn't flex so much? Or would a hi-tork servo be strong enough to hold it?
P.S. I'm already using a Sullivan anti vibration mount for the engine.
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Normen Strobel
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On Tue, 22 Jul 2003 12:56:51 -0400, "Normen Strobel"

You could swap in a fiberglass or carbon fiber tube for the majority of the existing rod, using 4-40 threaded ends. Hard to bow a tube. Cheers, Fred McClellan the dash plumber at mindspring dot com
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On my 1.20 Ultra Stick I use a tail mounted Hitec 605 servo and a 8" piece of 1/8" welding rod threaded 4-40 on the ends for the clevises.
Another option use a 3/16" thick-walled aluminum tube with 4-40 inserts at each end for the clevises.
Or fiberglass or carbon fiber tubes.
Prehaps use a 6" piece of brass tubing slid over the pushrod to give it some more rigidity.
On Tue, 22 Jul 2003 12:56:51 -0400, "Normen Strobel"

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I like your idea of sliding a brass tube over it. How thick is a 4-40 rod? I don't have a caliper on me. Is a welding rod that much more stiffer than a 4-40?
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Normen Strobel
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A welding rod is much stiffer, mainly because they are 1/8" diameter, and also a little heavier. But they are copper coated to help keep the steel from rusting.
There is a website ww.rodchuck.com that give a lot of information on using welding rods for pushrods and they alos sell the threading dies and a special holder for proper alignment.
I purchased my 5-40 & 4-40 die from www.microfastners.com about $4 each.
To thread a 1/8" welding rod you must first use a 5-40 die then re-thread 4-40, the RodChuck website gives all the details.
I would take the 4-40 rod with me and buy a piece of brass tubing that fits it. Most hobby shops and hardware stores have an aluminum/brass tubing display.
They are two types of threads cut & rolled, with each the diameter of the 4-40 rod is different but the same size brass tubing should fit both.
On Tue, 22 Jul 2003 20:13:47 -0400, "Normen Strobel"

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Install about 5 inches of Sullivan heavy duty plastic nyrod on the 6 inch elev 4/40 control rod.......Chas.
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On Tue, 22 Jul 2003 12:56:51 -0400, "Normen Strobel"

    Have a look at bicycle spokes. I find the ones I'm getting from the local bike shop to be stiffer than the DuBro 4-40 rods even though they are smaller in diameter. They're 2mm and will take a 2-56 die. The existing threads will take nylon clevises. Since the threads are cut rather than rolled the rod is bigger than the hobby 2-56 stuff.
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Your getting 1/4 inch each way (1/2 inch total) of oscillation in a six inch piece of 4-40 rod?? You must have some hellatious vibration going on. I would also be concerned with everything else in the tail with that much vibration. First I would try to figure out why there is so much vibration. I would use carbon fiber rod with threaded inserts for the control rod.
John VB

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inch
vibration.
You said it! If this was a 12" or longer rod (bad idea anyway) that >might< be one thing, but to see this kind of amplitude of vibration on a 6" rod is an omen. What's going on? And I'm not sure I agree with it "going away" in flight, I'd be nervous as heck about this. If this is elevator flutter/buffeting causing the flexing, then you need a lot more rigidity and strength. If it's vibration, then the vibration needs to be addressed.
I have tapped and bonded 4/40 ends into carbon tube (about 1" inset, thouroughly degreased and with decent epoxy) of appropriate diameter which is off the shelf at our LHS, and been very happy with the rigidity. They don;t seem to want to come apart or rattle.
Cheers,
Mike D
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I believe the vibration is because my 4 stroke vibrate exessively at low RPM. When I Rev the engine on the ground the vibration of the rod lessens.
I wish the local hobby shops around here carried carbon fiber tubes. I'll have to order some, probably from central hobbies with the 4-40 end inserts.
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Normen Strobel
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You could probably go to a sporting goods store and buy the same material in the form of a 3/16" graphite arrow shaft.
But you would still have to acquire some inserts.
On Wed, 23 Jul 2003 14:24:34 -0400, "Normen Strobel"

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On Wed, 23 Jul 2003 15:27:35 -0400, snipped-for-privacy@yahoo.com wrote:

Inserts ?
I use 1/8" welding rod and hard wood dowel stock which slip-fits into the shaft to make inserts.
Drill a 1/8" hole through one side wall 1" from the end of the shaft.
Cut a 1 1/2" length of dowel and groove it to fit the welding rod.
Bend the end 1/4" of the welding rod 90 degrees.
Butter the bent welding rod and grooved dowel with epoxy.
Insert the bent tip of the buttered welding rod into the shaft and poke the bent tip out through the 1/8" hole, then stuff the grooved dowel down into the shaft, locking the welding rod in place.
Ain't goin' _anywhere_.
Cheers, Fred McClellan the dash plumber at mindspring dot com
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Don't worry about it.
Just don't use metal control rods which are 2.5, 5, 10, 20, or 40 inches long. Cheers, Fred McClellan the dash plumber at mindspring dot com
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They work just fine, too. Got a bunch myself.
Original poster was pondering aluminum tube vice CF.
I was trying to dispell the myth that metal tube control rods are a strict no-no because of RFI. T'aint so . . . Cheers, Fred McClellan the dash plumber at mindspring dot com
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On Wed, 23 Jul 2003 14:24:34 -0400, "Normen Strobel"

Why not make your own and learn something new ?
Surf to http://www.acp-composites.com/ or https://www.cstsales.com/Carbon/carbon_push_rods.htm Cheers, Fred McClellan the dash plumber at mindspring dot com
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It's vibrating 1/4" on a 6" length. Wow. That's a lot of vibration.
I'd switch to a tube-type pushrod. Anything solid, unless very large in diameter and very heavy, will have a tendency to flex.

That's probably why it's vibrating so much. IMHO, "isolation" mounts often make the vibration from the engine worse. All they do is allow the engine more freedom of movement. There's still a point where the vibration shock ends up going into the airplane, no matter how it's mounted. The farther the engine moves before it "hits" the airplane, the more kinetic energy it builds up. That means it's actually hitting the plane harder, putting more stress on the airframe.
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