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linkage stopper - Printable Version

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linkage stopper - greggold - 18-03-2016

I have encountered a problem with the linkage stopper supplied with my HK Sbach 342 EPP 3D 900 mm airplane.
Linkage stopper is the term HK uses for the metal piece used to adjust a linkage by tightening a screw, as shown in attached photo (this is not the Sbach, just a photo I had that shows what is meant). The stopper in the Sbach is attached to each aileron servo arm with a threaded rod nut; the problem is the nuts vibrate and come off. If you tighten them on movement of the aileron they cause the pushrod to deform, and bend the servo arm and horn .

I have decided to remove the stoppers and use a z-bend at each end of the pushrod, with the z-bends orientated at 90 degrees to each other. I am using music wire K+S 0.047, which I get from Frontline Hobbies Newcastle where it is stock item KSE-0502. The advantage is that there is nothing to become loose. A disadvantage is that if you get the pushrod length wrong you have to start again and make another - however with a standard z-bender this is quick and easy, and the wire is cheap and comes in 36" lengths. I was able to use both pushrods in my first attempt.

In the tail the Sbach has short pushrods for both the servo arm and elevator horn, that both go into a length of heatshrink tube, then adjust neutral position, shrink, then add cyano. This seems to be working OK so far.

I would be interested to know if anyone defends the stoppers, or uses the above method or other methods.


RE: linkage stopper - dfw - 18-03-2016

as you said, stopper make it easier to adjust / center the servo connection.
Would it help to put some locktite on the stopper screw ?

RE: linkage stopper - kizza42 - 18-03-2016

I don't trust stoppers, too much potential for it to slip, even if you loctite the screw. To that effect, I don't like anything on my planes that isn't mechanically attached by > 1 point of failure.
As an eg, I don't rely on just velcro to hold a battery to a surface, it must also have a strap holding locking it in. Same with cameras....

Its not much of an issue with a light/slow foamy but anything larger than that really ought to have something more secure.

Z Bends are the way to go or if you want adjust-ability, clevis's or ball links and threaded ends for ultimate security.

You'll find ball links on high end stuff because there is next to no chance of slop in the linkage