Help! Adjust Linkage Length?

[Notorious B.E.N.]

I have an Extreme Flight 88" Edge that I recently changed out the elevator servos from Futaba S9156's to some MKS 777's. I don't recall there being a mismatch before but the elevator on the right side moves further than the left just by a little. Because of the programming in the radio, the center and end points do match.

So, to get equal travel through the entire range on each elevator should I try making the linkage a little longer on the left side and re-adjust center and end points or what should I do to get these servos to match up?

 

[Alky6]

Is it the same in both directions (up and down) or just one way? If same in both directions - easy adjust the end points lower or higher on one side or the other. If the elevator movement is more in one direction, IMHO, you should adjust linkage and centering of servo arm. That way it will more likely match throughout the range, especially when you start limiting throws for different conditions (you will find mismatches).

 

[Notorious B.E.N.]

Well, I have the end points set so they match at the ends currently. But the right is moving more up than the left in the travel and more down in the travel than the left until you get to the end points.

That is why I am thinking the right is slightly longer than the left and I should try increasing the length of the left just a little so they match throughout the entire travel.

 

[Alky6]

I believe I understand the issue now. If I restate and we assume the servo arm holes are drilled in the same location on each side, then it sounds as if the control horns on the elevator do not match from centerline to hole, correct? Essentially, the right side control horn length is shorter (measured from control point to centerline of hinge) than the left? So if you have adjusted endpoints for max throw, then if you use dual rates of something less, the dual rate max throw will leave the right elevator with more travel than the left. I would agree if you can adjust either the servo arm length or the control horn length, then you should be able to correct the problem. Have you measured the distances on the holes of the control horns to centerline of hinge?

 

[Notorious B.E.N.]

I have not because it's an EF plane and the control horns are the composite material that they use. I'm going to play around with the linkage lengths tonight and just make some minor turns and see if I can't get them to line up.

 

[Notorious B.E.N.]

This is what I'm dealing with.

 

[Alky6]

Looks like the servo arm geometry is off. Are the end points the same on the servos (meaning total degrees rotated the same)? If not set them the same so you get a better understanding and verify this, but to me it looks like the right servo arm needs to be moved closer (rotated towards) the elevator. That should speed up the down and slow down the up on the right elevator. I had a similar issue when I set up my JTEC. And it really didn't take much change to get it correct. Hope that helps. Good luck!

 

[Notorious B.E.N.]

I posted this on another site but in retrospect, I did not reset the subtrims to 0 before I put the arms on. I just reused the same settings as with the 9156's.

I'm going to pull the stabs and servos and redo the arms on the splines and see where I get. I had to adjust the subtrims and end points with the 9156's but since I had everything set to 0 when I started, it lined up in the end.

 

[Chrisk7]

Did you get your servo travels figured out? If so what did you find?

 

[Notorious B.E.N.]

I got them pretty close. I rezeroed the subtrims and got the servo arms as close to 90 degrees as possible. I think I swapped the servos to do that. Then I readjusted the endpoints. It's still not 100% perfect but it's not too far off.