Pull Pull Setup Help Please
04-24-2004 | 08:08 PM
#1
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From: Surrey,
BC, CANADA
Pull Pull Setup Help Please
HELP,
Gents I have setup the rudder on the Extra 330S using a single servo and pull pull cables. I haev found that when the rudder deflects one direction one cable is tight the other quite loose, yet at neutral position both cables are tight. I have been told my geometry is off which I accept as the correct answer so my question is as follows.
Where should the pivot point of my rudder control horns be?
Right on the hinge line?
Slightly behind the hinge line?
Slightly ahead of the hinge line?
The servo arm I am using is larger than the control horn on my rudder. Will that cause any issues? Also the servo arm on my rudder servo has some offset built into it, should I scrap that for something else?
Thanks in advance.
Gents I have setup the rudder on the Extra 330S using a single servo and pull pull cables. I haev found that when the rudder deflects one direction one cable is tight the other quite loose, yet at neutral position both cables are tight. I have been told my geometry is off which I accept as the correct answer so my question is as follows.
Where should the pivot point of my rudder control horns be?
Right on the hinge line?
Slightly behind the hinge line?
Slightly ahead of the hinge line?
The servo arm I am using is larger than the control horn on my rudder. Will that cause any issues? Also the servo arm on my rudder servo has some offset built into it, should I scrap that for something else?
Thanks in advance.
04-24-2004 | 08:28 PM
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From: Durham,
NC
RE: Pull Pull Setup Help Please
There is a term for where the control horn and the hinge line, line up. I can't think if it now but if you do a search on pull-pull you will find the answers. If not I'll help you look.
04-24-2004 | 08:33 PM
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From: Durham,
NC
RE: Pull Pull Setup Help Please
04-24-2004 | 08:49 PM
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From: Clemmons,
NC
RE: Pull Pull Setup Help Please
I have a 330s 33% that I just installed a pull pull on today and there is slack in one cable while the other one is tight at full deflaection. I thought it was normal. It might not be normal but my question is..whats the problem? I'm not being smart - just looking for answers.
Thanks
Thanks
04-24-2004 | 09:04 PM
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From: Rayne, LA
RE: Pull Pull Setup Help Please
the pivot point for your cables @ the rudder horn needs to be right on the hinge line, the distance between the two pull pull cables @ the rudder horn needs to be exactly the same as the distance between the two cables @ the servo arm. For example if you have three inches between the cables @ the servo arm you need three inches between the cables @ the rudder horn, regaurdless if you crossed the cables are not.
04-24-2004 | 10:19 PM
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From: Gales Ferry, CT
RE: Pull Pull Setup Help Please
It does not matter if one of the cables goes slack at full deflection, the surface will not flutter do to the aerodynamic forces places on the surface during deflection. The only cable doing any work is the one pulling. It is better to have the horn just behind the hinge than in front of it because if it is in front it will get tighter at full deflection and put more strain on your setup.
The pull pull horns and servo arms do not need to be the same size. It may be better to have a smaller servo arm for mechanical advantage.
Read the ackerman page. It is full of good info.
The pull pull horns and servo arms do not need to be the same size. It may be better to have a smaller servo arm for mechanical advantage.
Read the ackerman page. It is full of good info.
04-25-2004 | 07:27 AM
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From: Crete,
IL
RE: Pull Pull Setup Help Please
Original: Hooked-On-RC
The servo arm I am using is larger than the control horn on my rudder. Will that cause any issues? Also the servo arm on my rudder servo has some offset built into it, should I scrap that for something else?
The servo arm I am using is larger than the control horn on my rudder. Will that cause any issues? Also the servo arm on my rudder servo has some offset built into it, should I scrap that for something else?
04-26-2004 | 02:20 AM
#8
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RE: Pull Pull Setup Help Please
ORIGINAL: Stick Jammer
A servo arm that is longer than the control horn (measured from the pivot point to the hinge line) will create a mechanical DISadvantage at the servo. This is typically not the best set up as you are lowering the available torque of the servo. Keeping them the same length is the optimum set up for pull-pull. In regards to the offset, you would only need offset in the servo arm if there is any offset at the control horn present (pivot points substantially behind the hinge line). The control horn pivot point should be exactly on the hinge line or very slightly behind it, never in front of it. Set up in this manner, a straight servo arm of the same length as the control horn would be the optimum to achieve the correct geometry.
A servo arm that is longer than the control horn (measured from the pivot point to the hinge line) will create a mechanical DISadvantage at the servo. This is typically not the best set up as you are lowering the available torque of the servo. Keeping them the same length is the optimum set up for pull-pull. In regards to the offset, you would only need offset in the servo arm if there is any offset at the control horn present (pivot points substantially behind the hinge line). The control horn pivot point should be exactly on the hinge line or very slightly behind it, never in front of it. Set up in this manner, a straight servo arm of the same length as the control horn would be the optimum to achieve the correct geometry.
Would it not be accurate to suggest that you will lower the available FORCE of the servo verses the TORQUE? The torque value is a constant at the servo.
04-26-2004 | 07:44 PM
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From: Crete,
IL
RE: Pull Pull Setup Help Please
Yes, force would be the correct term in this example. Force would be measured on the servo arm at the point of attachment. Torque would be constant as it is measured at the servo shaft. 
05-04-2004 | 05:27 AM
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From: Delmar,
NY
RE: Pull Pull Setup Help Please
I have the Super Kraft control horns and they give me three pairs different sizes, short, med. & long. Which horns should I use for my pull/pull rudder, elevator and ailerons I am using the Du-bro super strength long servo arm for the rudder. I thought I should use the longest horns for the rudder but it is longer than the servo arm and doesn't deflect the full amount should I use shorter horns on the rudder?(if so where do I use the longest horns?)The horns are set up just behind the hinge line maybe a 1/16th I also get some slack in the cable which I can blame Ackerman for
05-04-2004 | 06:58 AM
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RE: Pull Pull Setup Help Please
Use the longest horns you have at both ends. Set the wires up in a manner that lets you move them in or out on the horns at both ends (servo and rudder). Set your servo travel for maximum travel. Move the lines in or out until the desired rudder deflection is obtained with the servo at maximum travel at high rate. The distance that the line is moved away from the center point, i.e., the center of the bevel on the rudder and the center line of the servo output shaft HAVE TO BE THE SAME. Do what you will with any excess horn length you may have.
