Servo neutral position
 

Hi,

was setting up a new model & while trying to set neutral for sometime, I found that the neutral position is not 90 deg to the servo body. No matter what I do, the neutral is slightly off. Further, the neutral angle on the lhs servo is not the same on the rhs servo as the servo arms are in opposite directions. I had seen this in the past as well and set it to exact 90 deg from subtrim but that results in shifting the neutral point which means the ailerons will deflect unequal & lead to non axial rolls. With the same problem on the elevators, the model may snap in 3d. The servos I am using are 5625mg and new. Is this normal & how do I correct this?

Ameyam

Well there is always some difference between the servos and sometimes reversing (change sides) or switching arms will help, but one BIG issue I see is the servos you are using. IIRC that was the first digital servo Hitec came out with and they are notoriously bad at centering and difficult to program.

I'd start by replacing the servos and then get yourself a Hitec programmer (assuming you stay with Hitec) and set 'em where you want them..... ;)

Actually, these are 2007 vintage servos but were in the box all along. Not sure wether they are prone to the problem you listed but I don't have any other issues with them. I picked up a few of these when a LHS sold out, so they were much cheaper than Tower and I don't intend replacing them

By the way, I have the same problem with a brand new 2013 7985mg I intend to use on the rudder. It's a single surface so it's less of a problem

Ameyam

If you are using a dual arm rotate it 180°. If a single arm remove it and use a dual arm, just remove the opposing end after finding the 90° end. All multi arms have a center in one direction. All single arms are made the same and depending on the direction will be off by one tooth.

Actually that is not correct for servo splines of 26. Futaba and some others are 25 spline.

I am using a GP aluminum arm with adapter. I tried a single stock arm as well. I didn't use the stock double arm. But the 7985mg was using the gp double arm with adapter
Ameyam

You can to rotate the adapter inside the arm and on the servo until you find the sweet spot. At least it worked for me with that arm.

Tried that

Last time I had this problem & asked around on the field, the club trainer told me he had a "micro servo adjuster" and said he would "change the centre & save it into the servo". Don't know what he was talking about as I didn't make that adjustment on that airplane. Was he talking about the servo programmer?

Ameyam

Yup, digital servos and a programmer. My experince the same as acerc. The arms are not symmetric regarding thier position when turned 90 or 180 degrees.

It gets even more interesting! Not a few of the models mount servos linkage, and horns in such a way that the linkage and servo position does not form a rectangle at center position.
At least most of the newer transmitters have the ability to correct for many of the problems.

Well, I didn't and usually don't use the stock linkages. I used Dubro blak scale horns and Sullivan full thread pushrods. So I will get that rectangle if I can figure the neutral

Ameyam