Retract Servo Question
 

First time putting together a plane with mechanical retracts. Does the plane require a servo that just travels 180 degrees?
I have a futaba S3170G retract servo and I am wondering if it will work. The plane is a Navy SNJ4 (similar to the AT-6).
Thanks.

Mechanical retracts require a 180 servo retract.

OK...thanks. I'm pretty sure that's what I have. It just goes 180 degrees...I think they called it a bang-bang servo.

The key to using one of those without binding is to take the retract and measure the throw of the pushrod from down and lock to up and locked.

Lets say it moves 1" for simplicity.

Measure the distance between the holes on the servo arms or better yet, get a blank wheel and drill holes. You want the holes spaced across the arm exactly 1" apart from each other. (not 1" from the center of the servo arm screw)

Any less and the legs won't lock fully, any more and the pushrods will bind.

I was wondering about that...thanks for explaining it to me. It makes sense now because I was wondering if there would even be enough movement to have the retract fully open then fully closed.
So for my own curiosity...why wouldn't a person just get a servo that moves more than 180 degrees and then it would be a lot easier to adjust to what you need?

If the servo rotaes more than 180º the pushrods will crash each other forcing the servo to smoke out!
Even at 180º it is possible you find problems due to pushrods movement fore and aft, not just out and in.......
If you can´t get a perfect movement adjustment I think it better to let the pushrods bind rather that not locking the gear due to a too short movement. Normally pushrods lengths and flexibility will allow for a little binding without further problems. By the way, proper retracts servos not only rotates 180º but also get disconnected at their end points, so they do not drain any battery on their extreme positions during flight and while on the ground.

The 180 degree will work fine...once I got it in place and made a few adjustments its good to go. I was concerned about the travel and the retracts opening up enough to be sturdy for landing but it looks good.

A little offset bend prevents any binding,, very simple to do

Not my video,, but a decent example

Nice video. Illustrates how it works perfectly. Thanks!