1/4 Cub glitching caused by ? - RC Groups
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Jul 23, 2012, 09:53 PM
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RC Erik's Avatar

1/4 Cub glitching caused by ?

Hey guys and gals,

I finished a 1/4 scale Cub with the PTE36R gasser about a week ago and flew about 9 flights with no problem.

But today for some reason, it causes all the servo's (except rudder) to sway back and forth just while the engine is running. And nothing was changed from the last 9 flights.

I thought everything was ok by doing the following on the build process -

Separate ign. electronics from rx electronics.
mag collars on elevator extensions
gold-n-rod for throttle linkage

Am I missing anything? Suggestions? Thanks in advance
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Jul 24, 2012, 12:23 AM
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mikmerl's Avatar
When you say the servos are swaying is it an erratic twittching?

What system are you flying?
2.4 gHz is quite immune to ignition noise.

Jul 24, 2012, 12:41 AM
Registered User
Could you have a chaffed or loose power wire?
Jul 24, 2012, 10:00 AM
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RC Erik's Avatar
I am flying 2.4 with the Spektrum DX6i. The swaying servo's are not so erratic but more of a consistent back and forth motion. kinda like waiving your hand motion.
Jul 24, 2012, 10:33 AM
1/2 scale
Sounds more like a trans. or rec. problem rather than glitching. Glitching is usually quick erratic movements.
You can still get interference with 2.4, as in....original chinese spark plug, ignition plug wire cap not fully seated on the plug, etc.

Try unplugging all of the servos from the rec., plug one in at a time to see if the problem shows up.

Battery good????
Jul 24, 2012, 09:23 PM
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rjstrickjr's Avatar
Definatly check all the extentions for nicks and bare wires. Also look at the routing of the wires. After 9 flights I would be more apt to look at the ignition wires and see if any of the vibrastions has caused a nick and may be grounding somewhere, Insure that the extentions are not laying or wrapped around each other. Are the sevos digital? One more cause could be a sevo going bad and back feeding into the reciever. Like the previous poster said check each sero individualy.
Jul 24, 2012, 11:31 PM
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RC Erik's Avatar
Thanks for the good info. I will definitely check it out.

I do not think it has anything to do with the rx or tx. Just because the problem only arises when the PTE36R is running. If the engine is off, the glitching goes away.
Jul 24, 2012, 11:37 PM
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adrian222's Avatar
I would check for any metal parts that are loose eg,exhaust,landing gear these can cause interference when they rub.
Jul 25, 2012, 08:36 AM
Registered User
Make sure the spark plug cap is fully locked on the plug. A little movement there can cause the symptoms you describe. It may have been "almost" fully on for the first few flights and vibrated off just enough to cause the problem.
Jul 26, 2012, 09:07 AM
1/2 scale
rc eric.

Have you found the problem yet? When you do, please let us know. Someone may be able to benefit from this.
Jul 26, 2012, 12:16 PM
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mikmerl's Avatar
RC Eric that swaying motion you describe sounds like it may be servo centering problems and nothing to do with RF noise or similar.

It may be the potentiometer wiper.
Are the servos new?
Which servos are they?

Try taking one servo apart and giving the potentiometer a good squirt of contact cleaner. You donít need to open the pot just find a small opening that they usually have and give it a good shot with the extension nozzle. Work the pot a few times with your hand and let it dry thoroughly before reassembling the servo.

Jul 27, 2012, 11:40 AM
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RC Erik's Avatar
Update on the glitcing Cub -

I talked with Troy Build Models yesterday for about an hour on the symptons and my set up. We concluded that it was not a frequency interference issue but rather a vibration issue.

Everything works great with the engine off. Even with no fuel in it and ignition on I can turn the prop shaft back and forth on the magnet to produce spark and no glitches.

BTW - the servo's are Hitec 645 metal gear high torque for everything except throttle. Standard Hitec servo for throttle.

I am going to have to check all the connections on basically everything.
Jul 27, 2012, 05:29 PM
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mikmerl's Avatar
I am using 625MG servos in my Giant Super Sportster with great results. There are one for each aileron and one each elevator half. There is a 645MG for the rudder.

About 50 flights now with a converted 31cc Ryobi weedi in front for power.

You must have horrendous vibration levels for it to cause such havoc on your servos after so few flights.

The component most sensitive to high vibration levels in your servos are the pot wipers.

I too have a Hanger 9 ľ scale J3 Cub (about 100 flights) with five 30 year old FUTABA S-131 servos that have performed flawlessly. The ZENOAH 23cc engine is an old magneto ignition engine that will run all day if you keep the fuel coming without missing a beat.

Let us know what your findings are, this is really a head scratcher.

Jul 27, 2012, 05:46 PM
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RC Erik's Avatar
Thanks mikmerl.

I might have my idle to low causing excessive vibrations.

Quick question - When you were talking about your servos, what exactly is the pot wipers?
Jul 27, 2012, 10:55 PM
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RC Erik's Avatar
Update on the glitching pain in the you know what Cub.

Tonight I covered the rx - y-harness servo reverser - and both batteries completely with foam. No hard mounts now. And still glitches.

I changed out the receiver with another known good receiver - still glitches.

Tomorrow I will swap out the ignition unit with a known good one and see what happens. If that still doesnt do the trick, I will probably gut the plane and start from scratch while checking every connection.

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