"1/2 A" & "1/8 A" airplanes These are the small ones...more popular now than ever.

Do I need rubber grommets?

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Old 09-09-2013, 04:37 PM
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shd3920
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Default Do I need rubber grommets?

I am building a Sig 36" wingspan Cessna L-19 Bird Dog. I will be using a Norvel .061 motor with mini servos.
I know when small planes such as this are electric you don't need the grommets. But for a .061 motor will there be enough vibration to need the grommets?
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Old 09-09-2013, 05:02 PM
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049flyer
 
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I have had problems with Hitec Hs55 servos hard mounted in 1/2a airplanes. Therefore I prefer to use HS81 servos mounted with grommets. If I were to use HS55 again in a small glow plane I would mount with grommets.

Therefore my opinion is yes, use grommets.
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Old 09-09-2013, 09:30 PM
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BMatthews
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Even small glow engines buzz like mini paint mixers. The rubber grommets is a good idea.
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Old 09-10-2013, 06:27 AM
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MJD
 
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And if they have the brass inserts, put the flange on the bottom, so it rests on the mounting plate and the servo "floats" in the rubber pinned by the flange and the screw head on top. If you put the flange up top, the brass can just drive itself into the mounting plate and compress the rubber too much - which takes away the nice vibration absorbing ability. I learned this way late in my RC career.. it is probably in the servo instructions which I don't recall ever reading. Anyhow the idea is not to compress the grommets beyond lightly snug.
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Old 09-10-2013, 09:27 AM
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Definitely use grommets on the servos. If your servos don't come with grommets you can always use fuel tubing. Either cut a small piece to wrap around the servo mounting tab, or a couple of small pieces to mount both above and below the mounting tab, use an Exacto blade to pierce a small hole in the tubing, and pass the screw through the tubing into the wood to secure the servo.

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Old 09-10-2013, 01:39 PM
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Quote:
Originally Posted by MJD View Post
...... it is probably in the servo instructions which I don't recall ever reading. Anyhow the idea is not to compress the grommets beyond lightly snug.
I've seen the over-compression happen too many times --- once the grommet is flattened, it is almost like a solid mount.

Ditto on MJD's comments on using the brass eyelets.
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Old 09-10-2013, 08:17 PM
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Definitely use them. They also give just a bit and can save you from stripping gears in a bind or unscheduled landing.
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Old 09-13-2013, 06:37 AM
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I try to be pessimistic, but why bother?
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Old 09-19-2013, 01:03 AM
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I hate to ask, but why are you wearing a hospital gown to build model airplanes?
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Old 09-20-2013, 02:01 PM
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Quote:
Originally Posted by CafeenMan View Post
I hate to ask, but why are you wearing a hospital gown to build model airplanes?
I met a guy while flying C/L back in the 1980s who invited me to come to his house and look at kits, built planes and engines he had for sale. This guy was obviously hobbled with an injury and had problems with his hands too. He looked to me like his "flying days" were behind him.

I showed up at his house with some cash in my wallet just in case he had something good. His house was littered from the front door to the back and from the floor on up with broken planes, unflown planes, engines, boxes full of spare engine parts, closets full of unbuilt kits, planes on tables yet to be finished...it was 100% control line stuff.
I kind of "searched" in my head for a polite way to ask him HOW he amassed all this stuff, but don't remember exactly how I phrased the question. He alluded to being in some sort of accident that had a big "pay day" and that part of the deal included an allowance for building C/L planes as part of his rehab..!!!!!

Last edited by combatpigg; 09-20-2013 at 02:05 PM.
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