pull-pull rudder better?
 

I was wondering what system is bettter for the rudder and why? Is it a pull-pull type of setup or is it the standard servo near the rudder with a standard control rod.I'm finishing up a mini 540 edge eflite kit and was just why one is better than the other,also I'm not thinking about doing to much 3D stuff just yet,if that is a consideration.

RE: pull-pull rudder better?
 

Hi!
Using thin fishing steel wires (pull-pull) is lighter than using Sullivan Golden rods or any other system and it doesn't transfer vibrations to the servos either.
And I don't like having the servos sitting out side on the fuselage...[:'(].

Regards!
Jan K
Sweden

RE: pull-pull rudder better?
 

Also considering using pull-pull system for a Goldberg Chipmunk. I'll be watching for answers in this thread too.

From what I hear they are lighter and work better than pushrods and golden rods. Just don't know the complexity of them.

RE: pull-pull rudder better?
 

Let me see if I can get this right. The way I understand it, the pull-pull should give you more positive deflection of your rudder. The reason for this is it is constantly pulling regardless which way you go left or right.With a pushrod set-up you have push-pull which means one way it pulls, & the other way it is pushing the pushrod which can lead to flexing of the rod giving you less positive deflection to the push side. The longer the pushrod the better chance for flexing I would think. There for with the short set-up out the side of the fuse would be less likely to have any flex in the pushrod while it is in the push mode.

I have the Mini Edge 540 by E-Flite too. I chose to go ahead & use the pull-pull that came with it. It was a hassle to set up, mostly because you are working with such little components, it is however working incredibly well now that I have managed to get it set up. It has very positive deflection in both directions I mean like right now!! I don't know that it wouldn't still be just as responsive set up the easy way with the cut-outs that are allready there for you to put the servo in the back. It is such a short distance for the pushrod I doubt you'd even notice the difference in performance, especially since you stated you're not really looking for 3D. The one thing you may want to consider with that particular model is balancing. With the pull-pull you get to put the servo up front & done this way I still had to get my battery as far forward as possible to get the CG right. If you put your tailfeather servos in the rear you may end up having to add weight to get it to balance. With a model that size weight is the enemy, any weight even just a few grams can make the difference. Bottom line is I think it's a better set up. The question is do you want to invest the extra effort to do it or not? It may not be hard for you at all, I got fat little fingers lol so it was all about the needlenose pliers & tweezers. You can use a piece of pushrod to carry the wire thru the fuse for ya. Turn it upside down & use the square cut out in the covering that is allready there to help ya see what you are doing. You'll get a little feeling of accomplishment once you've done it, I did.:) Good luck.

RE: pull-pull rudder better?
 

I took awhile to get the set ups right the first time. Now it is 4X faster than the rods.
It is hard to see Spider Wire fish line outside the plane.

RE: pull-pull rudder better?
 

If you decide to go with the pull-pull (a very positive type of control ), remember 2 things:

1. The hole on the control horn needs to be on the hinge line.

2. You need to have the same distance on the servo arm AND on the control horns on the rudder (or other control surfaces you have pull-pull on ). For instance, if the distance between the left and right control horns on the rudder is 2", the holes in the servo arm need to be 2" also.

RE: pull-pull rudder better?
 

If memory serves me there are tubes to run the wires thru from the tail forward & then you cross them over for the proper geometry for the pull-pull to work correctly. Referr to your directions, they spell it out very well.

As for the other method using the the cut-outs in the fuse. I am currently doing another ARF of the 60-90 size Dragon Lady which also gives you the choice of rear mounted servos & short pushrods. I chose to use them for this model for two reasons. 1) I'm using a good size engine & a smoke system so I put the servos in the back to help when it comes time to balance it. 2) It not a 3D type bird but more of a low-wing tail dragger #2 type plane. I haven't finished it yet, but I do have all the control surfaces in & the dual rates set. The push-pull with the short rods seems to work very well too. I don't see any flexing of the rods while pushing. The response time will be more than fast enough for me.

RE: pull-pull rudder better?
 

Hi!
No, you don't have to have the same lenght on the servo arm as on the control arm!
The way it works in practice (and in theory) when you have the servo arm shorter than the control arm is that one line is pulling and the other goes slack a little...but this is not noticeable...it works just fine.
The ideal set up of course is to have both arms the same length, but this is not necessary and most of the time not desirable due to the fact that you want leverage in the system.
I speak of larger glow or gas model here...in small (1m or less) electric models I would go for a carbon rod set up.

Regards!
Jan K

RE: pull-pull rudder better?
 

I agree with Jaka, you don't need servo arm and control horns at same diameter. You don't even need the holes on the control horn to line up with the hinge line. It is common, to offset these to gain mechanical advantage and/or to ensure crisp neutral by causing the non-working line to go very slightly slack at heavy deflection. I almost always offset and/or mech advantage my rudder pull/pulls.

I also agree than on small foamies, it is easier to setup and maintain push/pull setups as opposed to pull/pull setups. But this is personal preference and both setups work just fine. But the pull/pull could be made a little lighter. Probably not enough for night/day diff, but if you are going nuts for all out low weight, pull/pull can be made lighter.

Cheers

RE: pull-pull rudder better?
 

Thanks for all the info,I think I'm going shoot for the pull-pull system. It may a little harder to set up, but it seems like a good setup to know.Thanks again for all the input.

RE: pull-pull rudder better?
 

Go for it, you'll like it when your done.;)

RE: pull-pull rudder better?
 

Well it's been a few days now. Did ya get er done?

RE: pull-pull rudder better?
 

I would do the Pull Pull system on the Mini Edge 540. This will keep you from being tail heavy with the servo in the back of the fuse. Are you going with the inrunner setup or are you going to mod it and use an Outrunner motor?

RE: pull-pull rudder better?
 

How do you set up a pull-pull system? Don't you need to cut a pushrod exit on both sides of the fuselage to exit both rods (or wires???) to the control surface? If you need to, and both sides are cut out for, say, the elevator where do you cut the double exits for the rudder?

Please explain, graphics would help.

RE: pull-pull rudder better?
 

Minn is good at drawing graphs n stuff.

RE: pull-pull rudder better?
 

Tiger, in your example, you'd put the cutouts for the rudder either above or below the elevator cutouts. Doesn't really matter where they are as long as they don't interfere with other linkages. It is however common to run the rudder cutouts well above the elevator cutouts... often very high on the fuse, i.e. above the stabs. This also helps center the pull/pull linkage on the center of the rudder.

I have a pic, not the best, but see the black spot on the rudder... that is the control horn mount. If you look closely at the fuse right before the fin, you can see the fairings that protect the pull/pull exits for the rudder lines. They are very high on the fuse.

Cheers

RE: pull-pull rudder better?
 

Here's how I did both the elevator and rudder on my SSE