Decoupled closed loop system
 

Hi
I am trying to fine tune my closed loop set up on my Weston Groove.
Because of he geomtry of a closed loop system it makes it difficult to mechanically alter the throw.
eg the distance between the two closed loop pull pull wires at the rudder end should match those at the servo to make a perfect rectangle.

This is fine unless you want to change the mechanical set up. To maximise the servo throw with the desired amout of surface movement
So my idea is to decouple the wires from the servo and have them on a 180 degree bellcrank ( if there is such a thing) and then have a simple short pushrod connecting the closed loop bellcrank with the servo. I can vary the postion on the servo horn and therefore the resulting throw without ever effecting the closed loop geometry.
If I had an appropriate software package I would provide a sketch

So my question is has anyone ever done this before and if so where did you get the 180 degree bellcrank?
It also has the benefit of taking the load off the servo and making it easier to support.

Mike

RE: Decoupled closed loop system
 

Simple enough mike Ive in the past used a large double sided servo horn (Pete Tindal), with a brass wheel collet or piece of nylon bushing epoxied in the center as the idler bellcrank.

RE: Decoupled closed loop system
 

Photo shows the pull-pull bellcrank on a 33% L-4. Hardware is from [link=http://nelsonhobby.com/bell.html]Jerry Nelson. [/link]

Nelson have switched to single truss designs, but the bellcranks are still supported by double ball bearings and have zero slop.

RE: Decoupled closed loop system
 

Hi

I used this one which is readily available ( I think it is by Sullivan).
It is a simple thick nylon affair but after 50 hours in my CG Chipmunk it is still fine.
I have kicked rudder (by accident) and cracked the rudder by bumping it against the boot (trunk??) while packing it in and the servo gears have not been damaged.

It has the "Ackerman" (rotary to linear differential ??) built in - ie the holes are offset.