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94772's jittering in ailerons

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Old 08-07-2011, 11:26 AM
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Jetdesign
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Default 94772's jittering in ailerons

Mostly happening on right aileron, very slightly on left aileron. Tried swapping right/left ailerons, same results. Plugged elevator servo into aileron channels and it worked fine, so tells me the problem is in the servo itself.

Jitter comes mostly with returning to center, sometimes when powering up airplane (and it happens pretty violently), but can/will happen anywhere in servo travel. Happens more with faster inputs too.

Servos were new last year, maybe 100 flights on electric F3A plane keeping low rates and smooth inputs. SD10G radio, 6.0 volts from two independent regulated batteries.

Any ideas for home repair/adjustment/settings change? Maybe something with a pot? Or just send them in and deal with down time?

Thanks.
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Old 08-07-2011, 11:58 AM
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Default RE: 94772's jittering in ailerons

Hate to say it, but the latter.  The 772's are usually very solid, so I'm guessing the pots are worn. 
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Old 08-07-2011, 03:40 PM
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Default RE: 94772's jittering in ailerons

So sounds like a shop visit then. Surprised they didn't make it a couple hundred flights first, but things do wear.

Thanks.
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Old 08-19-2011, 06:59 AM
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Default RE: 94772's jittering in ailerons

Fortunately or unfortunately (and $35 later) Airtronics said they found nothing wrong. Bit of a head scratcher - installed a used set of Airtonics servos and the problem is gone. Hopefully it's an issue with the system somewhere that I can catch.
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Old 03-13-2012, 04:48 AM
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Default RE: 94772's jittering in ailerons

Hmm, forgot about this thread!

I finally got around to lowering the voltage of my system to 5.8 at the regs, still having the same problem. It's really noticeable, can't believe the techs didn't find anything wrong! Servo travels normally, but just as it gets close to the center it flaps around at a really high rate. Took me about 30sec to drop the servo in and see the issue.

Unfortunately, I don't even see a replacement pot for sale on the HP website??

I do feel compelled to drop in a plug for the 94761's - was doing some spring maintenance on the airplane and reworking the tail (adjusting linkage, sealing hinge gaps, etc) and I'm just baffled at how quick and smooth these little guys are, and at how well they work in unison. Gear train is still nice and tight, centering is perfect, and I can't see any difference in operating speed between the two. Hopefully I'll get my 772's working again and be back to Atx bliss
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Old 03-16-2012, 02:27 AM
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Default RE: 94772's jittering in ailerons

http://sanwa-denshi.com/rc/news/repo...ification.html
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Old 08-30-2012, 08:39 AM
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Default RE: 94772's jittering in ailerons

I hve a set of 94746 servos that did the same thing. Sent back to service and was told nothing wrong with them. But I am sorry they sit in the wing and vibrate so bad it can be felt on the whole plane. The aileron just twitches up and down. I have had digital servos from other brands and yes they all buzz a little but these things are over the top. No more for me at almost $100.00 each

No way I would try to fly them in my pattern plane.
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Old 08-30-2012, 09:18 AM
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Default RE: 94772's jittering in ailerons

Sit tight.  I just finished testing the 94747 - A direct replacement for the 746's and they rock.  They've toned them down for aircraft use (these were originally set up for surface cars which is why they were so tight) and they don't jitter at all.  I had the exact same experience with the 746's and communicated to them that they were unusable for the pattern market.   And low and behold they listened and the 747's were born.

90oz of torque, <.09 transit time (these are the preliminary specs) and they were ROCK solid.  Weight was good too at 1.6oz.   Not sure when you'll see them on the market but soon I suspect. 

I also tried the new 94770's which were also very solid.  150+ oz/in of torque and equally fast.  Again, toned down a little to avoid the jitters on our light ailerons.  Low current draw in flight from both of these servos.   These are full standard size cases and weight 2.1 oz so a little heavier.

Both would be great aileron choices and the 770's would make a good single elevator servo.  I believe the 770's are starting to ship now.


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Old 08-31-2012, 03:44 AM
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Default RE: 94772's jittering in ailerons

Great news . I will be in line when they come out.
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Old 09-06-2012, 12:41 AM
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Default RE: 94772's jittering in ailerons

How about the SDX-851? It looks like the air vision of the SDX-801 (94746) car servo.

http://sanwa-denshi.com/rc/car/servo/sdx-801.html

http://sanwa-denshi.com/rc/sky/servo/sdx-851.html

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Old 09-22-2012, 07:46 AM
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Default RE: 94772's jittering in ailerons

The service techs probably tests the servo with nothing on it but the servo arm at 4.8 volts. This is really stupid since it will not catch chatter unless it is already severe. The most normal cause of chatter is dirty pots.
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