Pull Pull set-ups............there seem to be a few comments here about slack developing when deflected and someone commented on distance between attachment points at servo vs attachment points at control surface.

Through trial and error and other modellers advice I've learned a few things about this. Recently read an article that confirmed what I learned. Will look for the article and post where it is because it was a great explanation and will probably do better than I will try to here.

For full mechanical advantage the distance between the attachment points of the cable at the servo and at the control surface should be equal. This will also result in a proportional movement of control surface to the movement of the servo arm. These measurments can be different and will not result in slack developing on one side when surface is deflected. Only down-side of these distances being different is that you won't be getting full mechanical advantage. No different than using standard control rod and using the closest hole to the center at the servo and the middle hole on the control horn.

The cause of the slack developing is another issue. If the attachment points at the control surface are not in line with the hinge line and the attachment points at the servo are in line with the servo output shaft you will get slack when deflecting the surface. If you want to you can off-set the attachment points but, you must make sure that the off-set is equal at both ends. Extreme wrong thing to do is to off-set at the surface behind the hing line and off-set at the servo ahead of the output shaft and you'll have serious problems unless you've used rubber bands for your cables If you off-set only one end of the system then you will get differential throw.

Hope this helps and if anyone else has tips for pull-pull systems I'd love to hear them.

OK so back to the point of this thread..............anyone want a used FT90?? I'm selling mine to be replaced with the ST4D


Cheers,
Dave