Pull-pull setup
 

Just a question for you guys out there: I have a scratchbuilt 1/4 scale Spacewalker w/ a saito 150 on it and this plane has pullpull on all the tailfeathers. Question is: how tight should the lines be (how much tension)? What is too tight and what is too loose?
Thanks in advance for your replies!!!!! John

RE: Pull-pull setup
 

John, you need to adjust so that all the slack is out and then about one more turn on each side. Depending on the material you use you may have to readjust again after several flights.

You do need to use ball bearing servos. Do not over tighten. Do not allow the cord/cable to rub or chafe on anything.

Here are a couple of photos that show how I do the pull-pull thing. The yellow tube is used only for a bearing which prevents chafing. By doing it this way, you don't have to make a straight shot from the servo to the horn. The Kevlar cord goes inside the yellow tube and a drop of CA is put into one end of the tube only to lock the cord to the tube.

Ken

RE: Pull-pull setup
 

Thanks Ken!! I am replacing the servos in the plane ( I didnt build it) as it only "had" Hitec standard servos :( installed on all the flying surfaces. I replaced them with 69 oz GWS servos.
I think my wires may be a little too tight cause I can just about play a tune on them LOL!!
Thanks again. John

RE: Pull-pull setup
 

I never attach the wires at the servo horns. I put an intermediate bell crank, so the servos move the bell crank and the wires betwen the bell crank and the horns in the control surfaces can be tight.
I have the same plane is a nice bird ant the engine you have is the best.
Good luck

RE: Pull-pull setup
 

I got the SWB Self adjusting rudder servo tray in the mail today and I've been fiddling with it.......pretty cool.

RE: Pull-pull setup
 

I'm a tiller man too. Just sent this to another person a day or two ago.
Edwin

RE: Pull-pull setup
 

I guess I'm just dumb and don't understand but why you go to the trouble of installing a secondary bell crank when the modern servos easily stand a balanced load? For several years I have flown pull-pull setups this way with no trouble at all. This includes my 33% Extra 300S (rudder) powered by a Brison 6.4 twin.

Tell me why you don't think a servo alone will do a good job. I'm willing to learn. Is it because you think John will be doing precision 3D aerobatics with his Spacewalker?

Ken

RE: Pull-pull setup
 

take a look at the Sig kit, this come with this system including a bell crank in the box.
Servo´s ball bearings can work better without the tension of the wires. It is my experience and I like to share with you.

RE: Pull-pull setup
 

Because the line tension puts an additional side load on the servo bearings above and beyond the load reflected from the flight control surface.

Using a tiller arm (bell crank) eliminates the line tension loading and allows the servo to deal with the normal loads for which it was designed.