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Old Jul 29, 2012, 04:00 PM
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Wabball's Avatar
United States, WA, Pullman
Joined Aug 2011
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servo acting crazy - jittering, shaking, etc.

Hello,
I recently finished building my scratchbuilt wing (DS2) and finally my electronics showed up from HK. I purchased a Turnigy Plush 40A ESC, Turnigy 2200kv motor, two Corona 929MG servos (http://www.hobbyking.com/hobbyking/s...dProduct=10345)

After finding where I wanted my servos to go, I cut into the foam and made a nice hole for them to fit into. I then centered the servos, put my pushrod holders on the arms, installed my horns on the elevons, and put in my pushrod. Before I put threadlock on the pushrod holders or glued in the servos, I went for a test run. One of the two servos is fine, but the other one just goes back and forth about 1mm very fast, just jittering and making it impossible to fly until I get this problem sorted out. I'm not sure what the problem is, I think the receiver is unlikely because I tried plugging it into another channel and it still does the same thing.

Right now I don't have a small enough screwdriver to open the servo, but if it has to be done I'll save it for a last resort. I looked around and read that the potentiometer could be the problem, but I think it might be the wire going into the servo. When I was installing them I was pulling the wire pretty hard, so maybe one of the solder joints is loose? Any help is greatly appreciated. Keep in mind these are brand new, out-of-the-box, "QC Checked" servos.
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Last edited by Wabball; Sep 03, 2012 at 01:31 AM.
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Old Jul 30, 2012, 04:55 AM
Confused? Who, me?
Roger Lombard's Avatar
United Kingdom, England, North York
Joined Jan 2005
4,790 Posts
I'm sorry Waball but the reason no-one else has answered your query may be that no-one wants to remind you that although these "are brand new, out-of-the-box, "QC Checked" servos. " they are also $4.55 servos and for $4.55 you get a $4.55 servo which is right at the cheapest end of the range. My experience is that if you want to be sure you get two working sub $5 servos in your package you probaby need to buy three. Otherwise expect to pay maybe twice as much.

Having said that, if you have a servo-tester - a very worthwhile investment if you haven't - then its worth trying to cycle the servo for five minutes or so to see if it cleans itself up.

Good luck.
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Old Jul 30, 2012, 08:55 PM
buyer of the farm
United States, FL, DeLand
Joined Mar 2009
4,742 Posts
A lot of times servo jitter is caused by a hinge that doesn't work right. Disconnect the servo from the control surface and see if it jitters then. If it doesn't you need to find out how that control surface is binding and fix it. When you stall servos they jitter. Free up the control surface and if the servo is okay the jittering will stop.
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Old Aug 03, 2012, 10:58 AM
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United Kingdom, England, Shrewsbury
Joined Jul 2012
26 Posts
I certainly think it is just a 'bad' servo myself, I had a servo go exactly the same way in my Parkzone Corsair! admittedly it was a used one by then but it just means the gearing inside the servo is knackered. New ones can get 'inferior' gear sets in them at the factory.

I personally would just by another servo! Futaba 3003's work well for me.

Kind regards

madon37s
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Old Aug 03, 2012, 12:50 PM
buyer of the farm
United States, FL, DeLand
Joined Mar 2009
4,742 Posts
Why in the world would you just buy a new servo without checking out all the easy and free stuff first? That makes about as much sense as buying a new car if you have a wheel out of balance.
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Old Aug 04, 2012, 10:23 AM
Registered User
Savannah, Ga, USA
Joined Feb 2009
479 Posts
I also use low priced servos, but at less than $10 consider them throwaway rather than spending time and money trying to fix. I agree with buying a couple spares just in case.
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Old Aug 05, 2012, 07:23 PM
buyer of the farm
United States, FL, DeLand
Joined Mar 2009
4,742 Posts
Oh, I agree with that. But if there is a problem with the hinge or binding in the linkage, changing servos will just wreck that one too. When do you stop changing out servos (and tossing them away) and just fix the problem? Throwing away a good servo never fixed anything.
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Old Aug 12, 2012, 02:08 PM
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RNAF's Avatar
The Netherlands
Joined Dec 2003
2,307 Posts
Try cleaning the potmeter.

I had a servo that jittered too. The pot was covered in white grease or something. My other servos have clean pots.

So, open up the pot and clean it. Also use a bit of contact spray. Saved me €13. Not much but money spent is money gone. Not to mention the time it would take to receive a new one
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Old Aug 13, 2012, 02:40 AM
Chris “Fly Baby” Greenshields
United States, CA, Huntington Beach
Joined Aug 2012
28 Posts
I always use quality in my planes. I fly Airtronics and like to put good quality equipment in my planes. Airtronics servos and receivers are always what I recommend to people. Start out right and put quality reliable equipment in from the beginning.

https://hobbypeople.net/index.php/airtronics/
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Old Aug 13, 2012, 05:12 AM
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The Netherlands
Joined Dec 2003
2,307 Posts
That's the basics of course, good point there.
My 5kg helicopter has quality parts throughout, my scratchbuilt foamies usually get cheapie stuff. My clone T-rex 500 has got cheap stuff too.
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