Why?

Rick:

Your approach seems like it might present a maintenance nightmare once your install is finished.

Did you reject mounting the servos under the 2" foam because of the swing arc length at the turnout with the servo mounted underneath the foam?

How do you plan to cover the servo?

Please know that I'm not criticizing. I'm struggling with using foam on a sectional wall layout and turnout control selection and installation is driving me crazy.

Jerry

My approach

Best way to describe it is show you a video of my servo control,

If it ever comes to working on it, just pop the turnout out and do what you need to.

The wood will keep any ballast from falling through.

This is an early "test" so some refinement is in order, but you will get the idea.

John

Answers for Jerry C.

Yes, I did reject mounting the servos under the layout for two reasons:

1.) I don't like working under the layout

2.) I may be covering the underside of the 2" foam with sound deadening material if I deem it too loud.

As far as covering the servo, it was in this original post - but underneath the picture:

I will be using a piece of tape with a washer attached underneath to cover the servo before scenery.  The washer will allow me to use a magnet to locate the servo should it need to be serviced or replaced.

Nice approach, John

I like your idea on the servo mounting -  thanks for sharing the video.

Maintenance of "buried" servos

I can't see my method as being a maintenance problem since the servos should little to no service.  In the event that one fails I will simply use a magnet to locate the servo, cut through the ground cover, remove the tape, and take care of the problem.  Once the problem has been resolved I'll just cover everything up.

I talked to some RC modelers about these servos and they said that they are very reliable.  Not one of them said that they have ever had one fail.  We shall see.

servo top mount

Hello Rick,

I'm glad to see more use of servos.  I have had mine for a couple of years with no problems.  My layout is table-top so I can't get under without a lot of lifting.  I mounted my servos to be accessible from the top with direct-drive - no spring wires.  The appeal of direct drive, as you have demonstrated,  is that the servos are programmed to set their own end-points.  The pressure on the point is firm but limited. Here is a photo.  When I get around to scenery I can bury the servo - reliability is high enough to minimize access problems.

RC aircraft control cable

I use this control cable, wire cable inside of a flexible plastic tube, to control my turnouts. Mine are manually controlled from the front of the layout, but you could use this line to run from your points to the servo which now can be placed anywhere on the layout. This way you could position the servos under removable buildings or any other places where access is easy.

The Line is pretty inexpensive, probably about a buck a foot up here in Canada (more than likely cheaper in the US) It also comes with a assortment of plastic and metal clevises that can be real useful when connecting the cable to things.

Servo Control

Will these push the micro-switches and/or Peco spring turnouts??

Brian,  That is a good

Brian,  That is a good question.  Since the servos can maintain pressure on the points it probably would be advisable to remove the springs from the Peco turnouts.  As far as operating the micro switches it would depend on the force necssary to move them.  I know that the servos have rating that are posted.

Brian remove the spring !

If you are ready to use a switch machine from Tortoise to servos, the best advice is to remove the spring of the Peco Turnouts, since the motors switch machines "locks" the point in place by pressure.

The force necessary to lock or unlock the in build spring in the Peco turnouts is big and can cause trouble with motors switch machine, further this could in time make to much stress to the throwbar and broke them.

servo overload

unless the servo reaches it's target position, won't there be excessive current drawn to constantly attempt to push the motor?

there's a difference between reaching the desired position and reaching it with some force required to maintain it.

Servo stall

With servos, you want to set the endpoints so that it stops naturally where you want it to stop.  If you run it up against a stop and hold it there, you’re stalling the motor.  Depending on how you have it powered, that could be just a little extra heat, to melting the servo or burning out the motor or stripping the gears.  I don’t know what the readily available servo switch control products do in that regard, but in general I’d recommend against stalling a servo.

Tortises on the other hand are designed to stall.

The Tam Valley controller

The Tam Valley controller that came with my servos gives extremely precise control over the end points thus assuring firm closing contact without stalling the servos.

Perhaps I am operating with

Perhaps I am operating with incorrect info?

I do realize that the Tortoise machines operate as a 'stalled' motor, but I assumed (perhaps incorrectly) that these little servos (used in model aircraft?) were NOT of the stalled type??

servo use feedback

servos are given a pulse (+/- 1ms) representing a position that the servo measures using a potentiometer.  It compares the measured pulse to the signal pulse and drives the motor one way or the other to make them the same width.

Servos aren’t supposed to be stall

Servos aren’t supposed to stall, but if you set them up incorrectly they could.  The feedback Greg refers to is not external, it’s inside the servo so the servo knows what position it’s arm is in.  In other words, it doesn’t sense when the turnout is completely thrown, it just keeps trying to rotate to whatever position you told it to go to with the pulse width you’re sending it.  If you haven’t configured the endpoints correctly that may cause it to stall.  Or, if you’ve gotten your hands on a sufficiently robust servo, it might instead destroy the turnout.  Those little translucent blue ones are pretty wussy though, they’ll most likely just stall.