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Turnout control linkage - linkage
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The Horn orientation creates an arc like a pendulum (a droopy arm hanging with your hand swinging). The linkage arc is in the opposite way, thus creating binding as the 2 arcs intersect 90 degrees to each other.
Mount the Servo with the gear axis (the screw) under the downward linkage line. Then bend the linkage downward. Place the linkage into one of the horn's holes, usually the middle one (of the 3 holes, the one closer to the gear axis will have more torque, less throw. The hole farthest will have less torque, more throw).
I mount a servo on a piece of U channel (assembly screw end down, horn up). Cut a slot in the 'top' of the U channel to allow the drop linkage to clear. Cut about half way down the wall, so that when you slide the 'C' it will allow the drop linkage to as as far as the horn's gear center.
If you measure the drop linkage, you can use a pair of pliers to hold the vertical piece, bending under the pliers 90 degrees.
Then hold this new horizontal bend and bend it down. Cut it off about 1/2" or less from the bend. This will poke into the servo horn. Place the servo up so it engages the dropped bend, then slide the vertical drop linkage into the slot until it is over the servo's gear screw.
It doesn't matter how exact the horizontal is bent under the turnout (how parallel it is the throw bar one above as you simply rotate the servo assembly until it centers the points, then screw it down).
These are picture from ANE Models (found by searching 'servo mounts model trains' on the web images.
A good refinement of the linkage Jeff. Under table clearance may sometimes require different configurations.
I've been using this type linkage forever. In my thinking it is the only way to go. Because of all types of different obstructions under our layouts, this type of installation allows the most options for placement. Forward or back of throw. Left or right of throw. Closer or further from throw. Use your imagination. do a little experimentation for your lengths of throws and you will be surprised at how many ways this linkage will work. I had a switch machine that I had to locate 12 inches from the actual turnout, works great.
Also using a spacer between the switch motor and the underside of the layout at times helps with the installation. And as stated, no large hole through the track bed. This makes the area much easier to ballast.