louisben36

Hi,
I seem to be having great difficulty setting up the cable rudder control on my Extra 260. Does the cable need to be taught or slightly loose? Also, do they need to be crossed?(right side of rudder to left side of horn).
I am getting a lot of buzz from the servo and it does`nt want to centre. I`m using an Hitec HS81 servo and a large dual servo horn.
Any suggestions please.

louisben

Walt Thyng

My Feedback: (9)

L/B: Hitec servos tend to buzz a lot. Cable tension should be taut, but not tight unless you are running them through an idler arm,then they can be a bit tighter. I don't understand your question about crossing the cables. The route they travel doesn't matter as long as it doesn't bind. The important thing is to have the same width between cables at the horn as you do at the servo. Perhaps that the root of your question about tautness. If the distance between the attach points is different at either the control surface or the servo, then the cables will tighten and loosen when the servo is moved.
Hope this helps.

Walt

louisben36

Hi walt,
thanks for your reply.
I think the width of the servo arm is not the same as at the horn, so maybe that`s where the problem lies.
Regarding crossing the cables......normally, the servo driving the control rod for the left elevator stab will be on the right of the fuse and vice versa, allowing a more bind free operation.
So i was wondering if the cables should cross over too on entering the fuse and be attatched to the opposite side of the horn to avoid rubbing.Hope that is a bit clearer...like mud
louisben

Walt Thyng

My Feedback: (9)

L/B: how you route your cables doesn't matter as long as they move freely (you ought to see the rat's nest on my Camel which has double cables to the elevator necessitating that they cross).

The dimension between the terminal points of the cables is what is critical. They must be identical! That's the advantage to attaching the servo end of the cables to (what I call) an idler arm. You can match it precisely to the distance between the holes on the rudder horn. You then drive the idler arm with a single pushrod from the servo. It also reduces the strain on the servo bearing surfaces.

You are quite correct about crossing pushrods to get a straighter run, but remember the pushrods exit the tail at different heights. Again as long as the cables move freely and do not cause radio interference, it doesn't matter if they rub or not or if they travel though several bends.

Walt
remember the only dumb question is the one that's not asked

louisben36

Hi Walt, that`s a great help thanks. Do you make the "Idler arm" youself or are they available commercially?

Walt Thyng

My Feedback: (9)

I imagine there are commercial units, but I make my own out of ply or an unused servo arm.
Walt