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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Without going into a lot of control
systems theory, the response of the servo is going to depend upon the mass it
is trying to move, the “stiffness” (hinges, push rods, etc.), and
the power of the motor (battery voltage). If changing the servo doesn’t fix
the problem then I would check the friction items in the path. The rubber bands
sound like a good possible cure as they will provide more damping. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='margin-left:.5in'><font size=2 face=Tahoma><span
style='font-size:10.0pt;font-family:Tahoma'>-----Original Message-----<br>
<b><span style='font-weight:bold'>From:</span></b> nsrca-discussion-bounces@lists.nsrca.org
[mailto:nsrca-discussion-bounces@lists.nsrca.org] <b><span style='font-weight:
bold'>On Behalf Of </span></b>DaveL322@comcast.net<br>
<b><span style='font-weight:bold'>Sent:</span></b> Thursday, August 24, 2006
10:01 AM<br>
<b><span style='font-weight:bold'>To:</span></b> NSRCA Mailing List<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [NSRCA-discussion] DS
8411sa Servo Oscillation on Rudder</span></font></p>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'><o:p> </o:p></span></font></p>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>Jon,<o:p></o:p></span></font></p>
</div>
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<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>It is basically a "deadband" issue, which is
always a compromise - tighter deadband yields more accurate centering but
increases the probability of oscillation (especially with heavy surfaces as has
been noted).<o:p></o:p></span></font></p>
</div>
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<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'> <o:p></o:p></span></font></p>
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<div>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>Since introduced, there have been some minor changes
to 8411, but Horizon should be able to increase the deadband for you.<o:p></o:p></span></font></p>
</div>
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<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'> <o:p></o:p></span></font></p>
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<div>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>Regards,<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'><br>
Dave Lockhart, Team JR<o:p></o:p></span></font></p>
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<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'><a href="mailto:DaveL322@comcast.net">DaveL322@comcast.net</a><o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'> <o:p></o:p></span></font></p>
</div>
<blockquote style='border:none;border-left:solid #1010FF 1.5pt;padding:0in 0in 0in 3.0pt;
margin-left:3.0pt;margin-top:5.0pt;margin-bottom:5.0pt'>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>-------------- Original message -------------- <br>
From: JonLowe@aol.com <o:p></o:p></span></font></p>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>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 co nverted 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. <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'> <o:p></o:p></span></font></p>
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<div>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>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.<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>Thanks.<o:p></o:p></span></font></p>
</div>
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<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-left:.5in'><font size=2 face="Times New Roman"
PTSIZE=10><span style='font-size:10.0pt'>Jon Lowe</span></font><o:p></o:p></p>
</div>
</blockquote>
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