ORIGINAL: goboto
... but I have a problem with the elevator. When I move the elevator I see the pushrod vibrating and bending a lot! I tried to pick the straightest, hardest balsa for the push-rods. Also, I'm worried about the bending push-rod because the servo has to push to make UP elevator. ...
GOBOTO;
To me; this indicates that you have the Elevator servo set up incorrectly.
From your description here it is travelling too far, the elevator cannot accomodate the amount of movement. Once it reaches it's maximum travel the rod keeps pushing and you get the bending and vibration.
Before you do anything drastic, if you have a computer radio adjust your End Point Adjustment. Reduce it to the point that you still have maximum deflection and no bending of the rod.
If you have a regular radio you are going to have to start playing with the control horns at both the servo as well as the elevator to reduce the effect of the movement. Basically, you need to move the ball link into the centre of the servo wheel, this will reduce the travel of the rod. Then you can put the control rod on the top of the Elevator control horn. As a last point of interest have a look at the elevator itself, is it free wheeling? or it it binding ? If you didn't shape the hinge points properly you could have reduced the amount of motion possible to the Elevator.
As they say; "The Devil is in the Details!"