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Pull-Pull woes
Hi all,
I just got a World Models Groovy 50 3A. It is a pattern ship and has a TT PRO 46 in its nose. I am using two Futaba S3004 servos for the ailerons and Hitec HS-475 BB servos for the rudder and elevator (one each). The rudder control is achieved through a pull-pull system which is stock supplied. Radio is Futaba 6XAS and the receiver is R127FD. This is my first time with pull-pull systems which I have just installed on it. My problem is that when i center the rudder stick after deflection on one side, the rudder does not come back to zero position. It stops just a little before that and I just have to give a slight bump on the stick (opposite side) to make it come back. When the deflection is on the other side, the rudder comes back properly to zero. I am using that thick red servo arm that comes with the servo and the pull-pull clevises are in the outer most holes of the arm. The cables are taught but not tight like a guitar string. I have tried my best to fix the problem but with no results. What do you all suggest? Cheers |
RE: Pull-Pull woes
It sounds like something is catching when you move it one way. Disconnect the clevises at the rudder end and move the rudder back and forth to see if that is the source. If not, get a helper to move the rudder stick while you hold the two clevises to see if you can feel some binding. If that doesn't work, reattach the clevises and remove the ones on the servo and try moving the rudder with them. Also move the servo back and forth to see if it's not centering correctly. One of these tests might help you find the source of the problem.
Something else that comes to mind is do you have the cables running parallel, or crossed? If they are crossed, they could be catching on each other. If they are parallel, perhaps one is catching where it exits the fuselage. It's ok to cross the cables as long as they are coated, or if you've tilted the servo enough to prevent the cables from rubbing each other. |
RE: Pull-Pull woes
ORIGINAL: rajeev Hi all, I just got a World Models Groovy 50 3A. It is a pattern ship and has a TT PRO 46 in its nose. I am using two Futaba S3004 servos for the ailerons and Hitec HS-475 BB servos for the rudder and elevator (one each). The rudder control is achieved through a pull-pull system which is stock supplied. Radio is Futaba 6XAS and the receiver is R127FD. This is my first time with pull-pull systems which I have just installed on it. My problem is that when i center the rudder stick after deflection on one side, the rudder does not come back to zero position. It stops just a little before that and I just have to give a slight bump on the stick (opposite side) to make it come back. When the deflection is on the other side, the rudder comes back properly to zero. I am using that thick red servo arm that comes with the servo and the pull-pull clevises are in the outer most holes of the arm. The cables are taught but not tight like a guitar string. I have tried my best to fix the problem but with no results. What do you all suggest? Cheers |
RE: Pull-Pull woes
Thanks for the quick replies, guys !
Chuck, I'll check up all you said and will get back here. Wxman, the wires are quite tight but not as in a bow string. I mean, if i pull the wire with my finger about four inches from the rudder control horn, it displaces for about half an inch. Rajeev |
RE: Pull-Pull woes
I've only done one pull-pull on the E-Flite Mini Edge 540. The instructions had me run the cables straight part way up the fuse then crossing over thru 2 holes in a former to create the correct geometry for it to function properly. Once I had everything lined up & pulled the wires snugly tight it worked like a charm.
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RE: Pull-Pull woes
Hi rajeev,
I had a similar problem recently with a hitec HS-81 mini servo. Try a different servo. |
RE: Pull-Pull woes
As everyone have given good advice, check the tension that the are close to equal on both cables. I was going to suggest a higher quality servo if all else fails. The 475 has good torque but is not as good as you can do for this application.
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RE: Pull-Pull woes
ORIGINAL: rajeev Thanks for the quick replies, guys ! Chuck, I'll check up all you said and will get back here. Wxman, the wires are quite tight but not as in a bow string. I mean, if i pull the wire with my finger about four inches from the rudder control horn, it displaces for about half an inch. Rajeev |
RE: Pull-Pull woes
I have to agree with gunfighter. Sounds like the servo has an issue.
Have you tried working the rudder with your hand before the servo install? Maybe pull the control horn and give it a go, see if you feel any binding? Are you useing stranded wire? A strand could be broke. Good luck and happy hunting. [8D] |
RE: Pull-Pull woes
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Hi!
The wires should not be tight as a bow string... on the contrary, quite slack actually, you should be able to press down easily if you press on the wire just a few centimeters from the servo arm. No sound should be heard, not like a bow string. I hope you use the thinnest fishing wire available, that's what you should use on most 1-2m span airplanes, pylonracres, scale as well as F3A aerobatic airplanes. Regards! Jan K Sweden |
RE: Pull-Pull woes
I agree with Jaka, make the wires as loose as you can and still get control. Make sure that you have a bit of what many call Akerman(spelling) installed. That is where the cable not being pulled actually slacks of a slight bit when the other cable is pulled. You do this by having the points where the cable attaches to the rudder horn very slightly ahead (forward) of the hinge line on the rudder. You can also do this by having the attach points of the control horn on the servo slightly ahead (forward) of the center of the servo arm pivot point.
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RE: Pull-Pull woes
is it forward or rearward for ackerman? i remember it to be rearward.
it's important that your rudder servo horn is absolutely perpendicular to the fuse when your rudder is at neutral, if you're using trim to get to neutral, then you're bound to have some issues. good luck! |
RE: Pull-Pull woes
Thank you all for your valuable suggestions. You all are a legend. I had a look at the problem this morning again. Seems that the location of the exit point in the fuse is wrong. Because of this, the wire is binding at the exit point. The fact that the wire is nylon coated and is not smooth (it is sort of ribbed) on the outside, it is causing a lot of friction with the fuse. I have cut the fuse to create a slit rather in place of a hole for the wire to travel. With this, the problem is more or less fixed. There is yet another problem that I need to fix and I hope after that, the problem will be fully rectified. This other problem is that the wires are touching the top of formers inside the fuse. I think I'll need to raise the height of the servo ever so slightly so that the wires go clear past the formers.
Thanks once again to all of you. Cheers, Rajeev |
RE: Pull-Pull woes
Glad to hear you found the problem. :D
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