Hello Guys,

Just wondering how people set-up the propped tension in pull pull systems, I will be more than happy if some one can explain to me a good way to do it because I don't feel comfortable with just touch and feel "that's how I actually do it"

For sure there are other ways.

Does tension matter? I mean you want it taut.. no slack.. but would it matter if there was 8oz of tension or 16? Im just asking as I don't know myself. I have setup pull pull on elevator on a foamy 450 size parkflyer and it seems to work fine with no special attention. i do have the proper setup as far as I know with parallel lines, etc..</p>

I think that tension make difference, because at the end is the free-play on the surface, when you just got them there without any tension it can even flutter, I don't know the right tension, don't even know what's matter to calculate it, maybe the servo?

The actual amount of tension is not all that important. All you need is enough to eliminate any free play while under load. Using too much tension will cause problems with hinges and servo bearings if the cables go directly to the servo arm.

Make it as taught like a bass string. When you "pluck" it, it should hum.

I clamp the rudder so it doesn't move then just make them taught, If I get too much servo hummmmm then they are too tight. It's just a fell thing.

Touchy feely works every time. Taught but not to taught. No slack may be a better term.

Make sure you use adjustable cable ends so you can take out the slack when the cable stretches.  This is a Dubro product in case you were wondering

There are principles to follow in a pull - pull installation.

The following is my idea and might not be agreeable to all readers.

There should not be any tensions creating a constant pull on the control surfaces horns and on the servo shaft.

The above mean that the lines should have a mminimum of any elasticity (should not be stretched).
Avoid nylon strings because they stretch too much.

The best material to use is stainless steel tiny wire available as material to hang picture frames on the wall.

At the control surface the horns should be installed so that the center of the horn connections are on a line passing through the hinge line and 90 degrees to the control surface.

The use of a threaded clevis or ball joint should be used at one end or the other so that the length of the wire can be set without loosenes and without much tension ; just not loose.

At the servo the axis of rotation should be just a bit behind (closer to the tail of the fuselatge) the points of attachment to the horn..
How much behind ?
That would depend on the horn radius being used at the servo.

The idea of having the servo axis of rotation a bit behind is so that the wire going back has a tiny more movement than the one pulling but without going slack.

If the length is quite long there should be some stabilizing points on the wire about every 6 inches..
Something like passing through a little tube that may be 1/4 inch long.justto prevent the wire from going into resonance like a wire could if under tension.

voila ___it is simple

Best of luck 2 U.

Zor

The most important part of a successful pull-pull is to have a bit of positive Ackerman built into the setup. Then just take out all the slack when at neutral, never tight enough to be able to pluck it and get a tune. With this set up, the line not being pulled as you move off center will go slightly slack (a good thing). If you goofed up and got a bit of negative Ackerman the non pulling line will get tighter as you move off center (a very bad thing which will increase current draw and servo wear). I have found nylon coated braided wire fishing line one of the best type of line to use. Also use the ferules from the same fishing line supplier to make your connections.

Rodney, I know how Ackerman line works, just wondering when you say positive, you mean closer to control horn? so basically it has two centres, the one that has the linkage to the horn needs to be closer to?

Thanks

Rodney

We are saying the same basic things. I avoided the word Ackerman as possibly confusing to beginners.

MuSo

I am a bit confused by what you wrote.

Zor

Well excuse my English if that's the issue :P

The Ackerman line basically was invented for a steering wheel so that the inside wheel was steering more than the outside, the amount of Ackerman is the distance from the centre of the steering wheel and the imaginative centre for the 2 wheels arms, in this case I just change the wheels arms for where the cable is connected to the servo, Now my question again with other words: is the imaginative centre for the two points that the cable is attached to, "positive" closer to the rudder?

Many thanks for the time expended to translate my English to good English.

http://www.rcuniverse.com/forum/m_72.../anchor/tm.htm

Ever wonder how we were able to set up a pull/pull before the Ackerman term was related to RC set up??

Thanks Red,

That was helpful.

Positive Ackerman is when the line NOT being pulled, goes slightly slack as the servo is moved off center. This can be achieved by having the cables attach points at the servo slightly aft of the pivot point on the servo or by having the attach points on the controlled surface arm slightly forward of the surfaces hinge line.

MuSo,

Nothing wrong with your English.

What I find confusing is that you seem to want to use differnt horn radius.

The horns on the control surfaces should have he same radius on each side and also on the servo if we wish to have symmetrical action.

At the servo the servo axis of rotation should be closer to the surface being controlled.

Zor

If you go to Allan's Hobby website, you will find an excellent bit of info on pull-pull systems and on Ackerman.Edited to add the web site address which is http://homepages.ihug.co.nz/~atong/

The Ackerman link in Alan's site does not seem to work anymore.

Zor