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Properly Setting up a Pull Pull rudder?????

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Properly Setting up a Pull Pull rudder?????

Old 04-17-2010, 12:48 PM
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trpastor
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Default Properly Setting up a Pull Pull rudder?????

I was wondering if anyone had an article on setting this up properly? I know some dual servo arms come with an offset, but I've never really understood the theory behind it. I'm sure it's fairly simple but if anyone can explain how to set it up (for maximum efficiency, minimum slop) I would appreciate it!

I'm assuming the servo arm should be the same distance across as the control horns on the rudder (so if you are using a 2 1/2" arm then it should be 2 1/2" from horn to horn). What does the offset on the dual arm accomplish?
Thanks
Old 04-17-2010, 10:15 PM
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LargeScale88
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Default RE: Properly Setting up a Pull Pull rudder?????

Not sure what you mean by the offset stuff. I just have a servo with a two arm hooked on it, the 4-40 pull cables, to control linkages on the rudder hooked up. Simple. Can you explain the offset stuff on the pull pull system some more?
Old 04-17-2010, 10:22 PM
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Default RE: Properly Setting up a Pull Pull rudder?????

The offset is called Ackerman geometry. It causes the cable that's not pulling to go a little slack at deflection and to tighten at center. The purpose is to let you adjust a nice, tight center without worry of binding.
Old 04-18-2010, 03:16 AM
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Default RE: Properly Setting up a Pull Pull rudder?????

Link to Ackerman: http://www.qmfc.org/school/ackerman.htm
Old 04-18-2010, 08:38 AM
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Rodney
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Default RE: Properly Setting up a Pull Pull rudder?????


ORIGINAL: trpastor

I was wondering if anyone had an article on setting this up properly? I know some dual servo arms come with an offset, but I've never really understood the theory behind it. I'm sure it's fairly simple but if anyone can explain how to set it up (for maximum efficiency, minimum slop) I would appreciate it!

I'm assuming the servo arm should be the same distance across as the control horns on the rudder (so if you are using a 2 1/2'' arm then it should be 2 1/2'' from horn to horn). What does the offset on the dual arm accomplish?
Thanks
The above reference to Ackerman is well worth reading and quite self explanatory. And, no, the servo arm need not be the same distance across as the control horns on the rudder. The distance from the hinge line to the rudder horn attach points can be longer than the servo arm with no problems. It can also be shorter but you need to be careful here. Check to make sure that there is no binding at extreme throw. If not, no problem if you make sure you have positive Ackerman.
Old 05-18-2010, 02:41 PM
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Default RE: Properly Setting up a Pull Pull rudder?????

If the cables go slack on both ends when the servo is turned, what can i try to fix this? I cross the wires. And am i correct in saying that both cables should be tense when the servo is centered, and the one not pulling when the servo is turned can be a little slack?
ORIGINAL: Rodney


ORIGINAL: trpastor

I was wondering if anyone had an article on setting this up properly? I know some dual servo arms come with an offset, but I've never really understood the theory behind it. I'm sure it's fairly simple but if anyone can explain how to set it up (for maximum efficiency, minimum slop) I would appreciate it!

I'm assuming the servo arm should be the same distance across as the control horns on the rudder (so if you are using a 2 1/2'' arm then it should be 2 1/2'' from horn to horn). What does the offset on the dual arm accomplish?
Thanks
The above reference to Ackerman is well worth reading and quite self explanatory. And, no, the servo arm need not be the same distance across as the control horns on the rudder. The distance from the hinge line to the rudder horn attach points can be longer than the servo arm with no problems. It can also be shorter but you need to be careful here. Check to make sure that there is no binding at extreme throw. If not, no problem if you make sure you have positive Ackerman.
Old 05-18-2010, 04:02 PM
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Top_Gunn
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Default RE: Properly Setting up a Pull Pull rudder?????

If the cables go slack on both ends when the servo is turned, what can i try to fix this? I cross the wires. And am i correct in saying that both cables should be tense when the servo is centered, and the one not pulling when the servo is turned can be a little slack?
The last sentence is right. If you've got the Ackerman correct, that's what will happen. I don't understand how turning the servos could make both cables go slack. When you turn the servo, one cable is pulling, all the way; how can it become slack? Pulling on a cable can't loosen it, I think. Of course, in your shop the rudder is free to turn, so it might get bumped and you'd end up with both cables a little slack, but that wouldn't happen in the air because the air hitting the rudder would oppose the pulling motion.
Old 05-19-2010, 12:53 AM
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Barns
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Default RE: Properly Setting up a Pull Pull rudder?????

Thank you, this now means that the rudder is ok and i can go maiden my pilot rc Yak. I hear it flies great, so hold thumbs.
Old 05-19-2010, 01:09 AM
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perreback
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Default RE: Properly Setting up a Pull Pull rudder?????


ORIGINAL: Barns

Thank you, this now means that the rudder is ok and i can go maiden my pilot rc Yak. I hear it flies great, so hold thumbs.
Will do. We'll cross our fingers as well, for good measure. Good luck.
Old 05-19-2010, 05:58 AM
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da Rock
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Default RE: Properly Setting up a Pull Pull rudder?????

ORIGINAL: perreback

Link to Ackerman: http://www.qmfc.org/school/ackerman.htm
That link is to an excellent explanation, complete with illustrations.

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