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Old Nov 08, 2009, 10:05 PM
cptsnoopy is offline
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Offsetting constant spring pressure on servo with counter force spring?


I have heard and read some discussions involving using a cable/spring setup for elevator and rudder control. I understand that there is a constant force applied to the servo causing additional drain on the battery. Would another spring used in the opposite direction attached to the servo arm at the same distance out as the one used at the elevator/rudder (arm length) a plausible idea for reducing loads on the system? Maybe this is already done, I would not have a clue as I personally have not used this system or even seen one in person. Just curious.

Charlie
Last edited by cptsnoopy; Nov 08, 2009 at 10:23 PM.
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Old Nov 08, 2009, 10:10 PM
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On further thought, the pivot distance at the servo would not be feasible as there is generally not much room where the servo is mounted. Perhaps a stronger spring would be required because of the shorter arm length at the servo.

Charlie
Old Nov 08, 2009, 11:19 PM
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I think the whole idea is to save weight which the additional spring would defeat .The real cure is push/pull but it weights more than pull/spring SL
Old Nov 08, 2009, 11:55 PM
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What's wrong with good old stainless? It's low maintenance and it typically works.
Old Nov 09, 2009, 12:38 AM
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Quote:
Originally Posted by soarluck View Post
I think the whole idea is to save weight which the additional spring would defeat .The real cure is push/pull but it weights more than pull/spring SL
Push/pull is what I use. And so far I have not needed to reduce the weight enough near the rudder/elevator to consider using pull/pull or pull/spring. But if tail weight was an issue and pull/spring is lighter then maybe this would help keep the CG more in line.

Perhaps the constant strain on the servo is not enough to worry about? I was under the impression it might be an issue.

Charlie
Old Nov 09, 2009, 01:09 AM
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I have used the pull-spring method on my DLG for a few years now. At first I was skeptical. I did worry about the constant spring tension on the servo. I'm using it on a full flying stab, analog servo. No issues with draining the battery, servo's are not failing and seem to be centering just fine.
Old Nov 09, 2009, 01:29 AM
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Originally Posted by dbaya View Post
I have used the pull-spring method on my DLG for a few years now. At first I was skeptical. I did worry about the constant spring tension on the servo. I'm using it on a full flying stab, analog servo. No issues with draining the battery, servo's are not failing and seem to be centering just fine.
Ok, sounds like it is a non-issue. Thanks

Charlie
Old Nov 09, 2009, 01:54 PM
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I'm using pull/spring on my new Predator. The spring part is a small rubber band. What's nice about the system is that you can take the rubber band off for storage; no tension.

John
Old Nov 09, 2009, 04:22 PM
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Normally the geometry means that the force on the servo at-rest, is taken up by the friction in the gear-train.
Old Nov 09, 2009, 09:53 PM
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Quote:
Originally Posted by cptsnoopy View Post
Ok, sounds like it is a non-issue. Thanks
Charlie
Charlie,
I use SS wire which also doubles as the antenna.
However, increased battery load has been suspected, but I've not seen it measured.

With 1900+ post you've been around a while and you may just have a WattsUp power meter, or have a power flying buddy who has one.

The WattsUp measures peak amps and also amp/hours. You could hook it up in series with your Rx find out just how much load the spring is giving compared to swinging the servos with no load.

BTW, the Ah reading has to be divided by hours or parts of hours to get average current for the transient servo load.
I'd like to know too.
Good luck.
John255
Old Nov 11, 2009, 09:31 AM
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Whoa!!
Didn't mean to shut down the thread!!
It was just a suggestion to settle the guessing.
John255
Old Nov 11, 2009, 09:50 AM
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Hi John,

I have been preoccupied with work this week which has left zero time for testing the concept. You have done nothing wrong.

Charlie
Old Nov 11, 2009, 10:31 AM
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Last edited by kcaldwel; Jul 01, 2010 at 08:37 PM.


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