Servo question

[Helifino]

I'm using hitec hs-55's on my trex 450xl.

Is it possible for servos to come to center from one direction and not the other?

Here's the problem I've had from day one. When releasing left aileron stick on tx, swash returns to level. When releasing right aileron stick on tx, swash sticks in place and doesn't return to level. When releasing up elevator, swash levels. When releasing down elevator, swash sticks and doesn't return to level.

If linkages are removed,servos center each direction. With linkages attached, servos only center from one direction. All ball links fit well. Converted earlier to cde from hde and did same thing. Converted back to hde from cde and same thing. Installed metal parts on head and same thing.

Is it possible the servos are sticking under a load and can't handle it(does that make sense)? :confused:

[broke-again]

From what you describe, I would have to guess that you have a "sticky swash" or defective servo. Its really a process of elimination.

Apply a very small drop of 3 in 1 oil or white lithium grease to the swash where it meets the main shaft and work it in. If problem persists -:

(1). Check/replace the main shaft.

(2). Check washout arms for free movement.

(3). Check all ball links.

(4). Check flybar seesaw for free movement. A worn or damaged bearing here can cause what you describe.

(5). Try another servo.

(6). Replace swash.

For the 450 heli your really better off with HS65 servos - if your budget allows get the metal gears. They are "Fit & forget".

Anyway, good luck - let us know what you find.

[cbflys]

A common cause of this is the elevator and/or aileron arms slipping on the shafts because they're hitting their limits of available travel. Take off the pushrods going to the servos and move the pushrods manually. See if anything slips. Also - as stated above; check for free (non-binding movement.

[Helifino]

Thanks guys.

I know it's not the swash,because it did it with the plastic hde,plastic cde and now metal hde swash. I think I can eliminate the ball links because it did it before I resized them, after I resized them and after I replaced them all. Washout arms were replaced with metal ones.

I will check for arm slipage and flybar seesaw.

I've been eyeing up the 65's for awhile now, guess it's time to break down and get em.

Thanks for the input! :)

[tdswan]

HS 55's are crappy servos in general, I've got 'em on my CDE as well. They are not terribly accurate to start with. I can put a pitch curve on it,then do it right away again and I'll get different numbers. There are a lot of linkages and bellcranks on the bird and on top of the rotor assembly. Yes, the linkages binding and over-all slop in the whole setup are probably the majority of the problem, use some Tri-Flow on the swash and make sure each ball-link end is so free you can breathe on it and make it turn on the ball. Doing my mod in this section will also help. That elevator linkage is full of friction.

[Helifino]

Well td, your right about the 55's, the are crap with a capitol "S" and that don't stand for smooth! I will also try the tri-flo again(it didn't seem to help before). I'm still getting the 65's regardless. Giving serious thought to your mod, great job by the way. Maybe align will pick up on it! :)

[tdswan]

I see dollar signs! :D $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$