[NSRCA-discussion] DS 8411sa Servo Oscillation on Rudder

[Grow Pattern]

Jim,
        The "rubber bands" were left over from my electric days. You should 
have some spare ones as well!!!! (VBG)

One method that I forgot to mention is that when I swapped in sing;le wire, 
as opposed to multi-strand, pull-pull wires, the oscillations stopped. With 
a heavy or large surface the multi-strand pull wires stretch a little and 
this definitely aggravates the "center-hunting" condition.

Eric.

----- Original Message ----- 
From: "Jim Woodward" <jim.woodward at schroth.com>
To: "'NSRCA Mailing List'" <nsrca-discussion at lists.nsrca.org>
Sent: Thursday, August 24, 2006 12:28 PM
Subject: Re: [NSRCA-discussion] DS 8411sa Servo Oscillation on Rudder


I get a kick out of these threads about installing new JR gear sets, and we
can now add, using rubberbands on them. :)

Jim W.
Team Futaba



-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of
jonlowe at aol.com
Sent: Thursday, August 24, 2006 12:21 PM
To: nsrca-discussion at lists.nsrca.org
Subject: Re: [NSRCA-discussion] DS 8411sa Servo Oscillation on Rudder

Jim,
This only manifests itself at neutral, and both cables are tight.
Nothing is slipping, and I don't use ferrules.  In this particular
case, I don't see how ackerman would be involved.

Jon

-----Original Message-----
From: jivey61 at bellsouth.net
To: nsrca-discussion at lists.nsrca.org
Sent: Thu, 24 Aug 2006 7:21 AM
Subject: Re: [NSRCA-discussion] DS 8411sa Servo Oscillation on Rudder

Jon
Read this about pull-pull.
This will also happen if your cable ends slip. If you put the cable
through the ferrule just one time it may be slipping. Bad geometry will
cause this also.

Jim Ivey



http://members.cox.net/bdfelice/Ackerman/ackerman.htm
----- Original Message -----
From: JonLowe at aol.com
To: nsrca-discussion at lists.nsrca.org
Sent: Thursday, August 24, 2006 7:38 AM
Subject: [NSRCA-discussion] DS 8411sa Servo Oscillation on Rudder


I'm running a JR 8411sa on rudder on my Aggressor, pull-pull, using the
setup that Troy Newman recommends (ss control line cable, NMP links at
the servo end, and MK links at the rudder, etc.). For the first 75 or
so flights, I had no issues. Then, the servo started self oscillating
around neutral, even with the engine not running, on the ground if the
rudder stick was bumped. The surface buzzes back and forth about 1/4",
until damped out by grabbing the surface. Thinking it was a servo pot
going bad, I changed out the servo. After two or three flights, same
problem appeared. Then thinking it must be a natural frequency issue
in the linkage exciting the feedback loop in the servo, I tightened up
on the pull-pull somewhat. It wasn't loose before (these cables, as
Troy says, don't stretch at all), but I increased tension somewhat.
That helped for about 3 flights, then the problem reappeared. These
servos are new 8411's, self converted to SA with a new plastic gear
package. I've gone thru the linkage completely, and find no evidence
of anything amiss. I've changed nothing in the setup from the
first flight.

I believe I read somewhere in the past, about some 8411's doing this
because the feedback loop in the servo was too tight, and could be
corrected by sending them back to Horizon. Can anyone shed some light
on this? I'm about to install an 8611 on rudder, but would like to
track down this issue with the 8411s.

Thanks.

Jon Lowe



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