Pull-Pull Rudder Setup Help
 

Hello. I have a Sig Extra 300XS 1/4 scale plane with a OEM pull-pull rudder system. I have tried making the wires moderately tight to very tight. No matter what, the rudder will not come back to absolute center. Say I give full right rudder, when I let go, the rudder won't return back to neutral. Same with the left side. I have tried trimming and sub trim. Nothing is working. I feel I need more tension but I have it I believe way too tight right now and the problem is still there. Does anyone have any suggestions?

RE: Pull-Pull Rudder Setup Help
 

The pull pull wires do not and should not be guitar string tight-it will put too much stress on the servo and related items. Either the rudder is not free enough or the servo is not centering-its not in the wire tension. Just taunt is fine-do some comre checking and let us know what you find-assuming you are using plastic coated cable or kevlar.

RE: Pull-Pull Rudder Setup Help
 

you don't want the wires very tight. full scale uses very little tension on the cables and some small airplanes have none and use springs on the rudder pedals to keep the cables tight. it may be your servo does not return to the same center, I have had this problem. or it may be to much friction in the hinges, there should be virtually none.
Charliek

RE: Pull-Pull Rudder Setup Help
 

I use pull-pull on most of my planes, big and small. I have found that I leave the lines as loose as possible, just enough tension to keep them from saging or jumping off a pulley when I use a pulley. You may have some reverse Ackerman (a term that is occasionally used to describe the offset of the attach points relative to the hinge center line). I usually deliberately put in a little Ackerman so that the cable not being pulled goes slightly slack when the other cable is pulled off center yet have both cables just snug when the surface is centered. I do this by having the attach points at the horn on the surface a very slight distance behind or aft of the hinge center line. It can be done at the servo side also by having the attach points slightly ahead of the pivot on the servo arm. In any case, make sure that the surfaces move freely when the control lines are not connected, i.e. free and all hinge lines on a straight line with no friction.

RE: Pull-Pull Rudder Setup Help
 

okay sounds good and thanks for the advice. I will have to wait until I get home to figure it out. I am using a Futaba S3305 high torque MG servo. I have another S3305 so I will switch it out and see if the servo was the problem. I am just using the stock wires I do not know if they are coated. I have the wires going through the servo arm and being crimped by aluminum tubes and on the rudder end I have a threaded connecter to adjust wire tension. I will stay posted on here and thanks everyone.

RE: Pull-Pull Rudder Setup Help
 

Varad,

There is part of your problem... the S3305 is a nice servo but sloppy around center. I use them on big Ailerons but avoid them on Elevators and Rudder.

Good Luck,

Hibrass

RE: Pull-Pull Rudder Setup Help
 

Check to make sure your hinges (if CA or of similar type) aren't buckling under the load.

RE: Pull-Pull Rudder Setup Help
 

thanks for the help everyone. I had a new S3005 around and switched it out with the old S3005. I put mild tension in the system and it's working perfectly now. It now goes back to complete center. like charliek said, my servo wasnt centering. Hibrass, should I get a better servo for the rudder? Right now it seems fine. Again thank you.

RE: Pull-Pull Rudder Setup Help
 

Varad,

To me it depends on the type of plane and flying you are doing... If you are just 3Ding and Bashing use the 3305 and enjoy... If you are shooting for percision batics, get a more precise servo...

I would just run the 3305 unless it causes you flight trim problems...

Good Luck,

Hibrass

RE: Pull-Pull Rudder Setup Help
 

okay i will just stick with it for now. It seems fine but I didn't fly yet.