Joe B.

My Feedback: (1)

I have a new Sig Cap 231EX. My poor self decided to put GWS servos (hi torque) on the elevator and ailerons since I didn't think my standard 94102's would be enough (50oz @ 4.8v and I think 65oz @ 6.0v).

The reason I am asking is my plane is flying terribly. I take off and it feels like it is tail-heavy. I know it's not as I'm about 1/2" ahead of the recomended CG and have verified with others with same setup of their CG and I'm not tail-heavy. I've noticed the control surfaces don't always return to the EXACT same position as they started in (by very small amounts but noticable) and there doesn't appear to be the resolution with these POS servos. Can poor centering cause the plane to fly like this? Like it's out of trim constantly and react wildly to input? Man I'm afraid to fly this plane now. I'll be putting the 94102's in it to test out and if they work I'll get some Hitec 605BB's in their place.

- Joe

branded

My Feedback: (9)

Servo centering isn't the important relevant parameter when judging a servo, it's "deadband"......

Here's why.....

Sometimes the servo motor cannot overcome the drag of its own gear train, as well as the drag of your control linkages, the weight of gravity on the control surface as it hangs from the airframe in order to reach center, or so it seems when observed on the ground.

It will simply sit there and buzz slightly.
Now here's where some common sense comes into play. Try imagining the control surfaces, and the force on them, as they would experience while in flight.

The air stream will overcome this slight amount of drag and allow the servo to center by virtue of the force of the airstream and the resultant force reflected back to the servo arm.

The fact is, while flying, as a result of the reflected force transmitted back to the servo via the linkage, will cause the servo to average it's position around the dead band of the servo, plus or minus.

I hear so many times servo centering as a measure of the quality of the servo, and fellows agonizing over the seemingly inability of their servos to "center".......

As you can see, it's not really indicative of anything important. Practically speaking, in the typical setup, there's more slop in the linkages than can be measured in terms of errors introduced by servo "no centering".

The new digitals, as well a coreless, appear to have better centering and satisfy the casual observer on the ground. They however expend great amounts of power to achieve this ability. The practicality of using them in a given setup is wholly dependent on the "tightness" of the linkages...If you have sloopy, or loose linkages, then you're wasting time using expensive digitals or coreless servos.

I hope I've given you some perspective here concerning the mechanics of our servo systems......

Joe B.

My Feedback: (1)

I have noticed that on my ailerons for instance, if I give right aileron (on the ground looking) and then release, the left aileron will be just perfect with the cutou. If I give left and release, it will be a hair lower than previous position. Repeat with right aileron and it goes center. On elevator, I have a y-adapter (w/reverser) and if I give full up and release, one elevator goes straight to center, other goes slightly past, then returns. If I give full down, it's just the opposit. This makes me think it's something in the servos and that in one direction they can't center well (or at least on first try). Maybe deadband is the appropriate name, or maybe not. I just now my plane wouldn't hold a trim setting and seemed to be very twitchy, almost like it had 'steps' and not a linear rate. Ohh well, i'll try some others and see if they work better