Post 7 from my old blog (from ~2011)

I’ve been working on low cost ways to control turnouts. I bought some servos (AU$7 for 4) on eBay and tried to operate my hand made turnout with one of them. Here is a picture of the initial setup:

Servo Controlled Turnout

Servos need about 5 volts plus a pulsed control signal to work. I’ll eventually use a microprocessor to generate the pulse, but for now I’m using 555 timers. The circuit on the breadboard contains two 555 timers. The first timer generates a continuous pulse 50 times per second. This pulse triggers the second timer which then produces a pulse between 1 and 2 ms, depending on the knob.

UPDATE 2018: These days I would just use an Arduino to control the servo. Also, the circuit I used is no longer available on the internet but I am sure you can find one if you want to use 555 timers.

The servos look like they may be sort-of OK to control a turnout, but there are two problems. The first problem is that the servos make a bit of noise when moving to a new position. They also tend to buzz quite loudly if put under strain - like what happens when a point rail is pushed or pulled tightly against a stock rail. The whole lot is amplified by being mounted on some fibreboard as in the picture.

The first problem should be able to be reduced by some sort of isolation in the mounting, but the second problem will require careful setting of the pulse endpoints. These endpoints are the minimum and maximum length of the servo control pulse. These will have to be user configurable in some way as they will vary from turnout to turnout.

Just the other day I came across an interesting website on using servos to control model railroad turnouts. It looks much easier than my setup as it doesn’t require much to hold the servo. I will give it a try and see how it goes.

The website is Tamalpais Valley Railroad. He also has a schematic for controlling up to 4 servos using a micro-controller.

UPDATE 2018: Since I started experimenting with servos for turnouts around 2010 they have become quite popular for turnout control. Googling will bring up lots of hits with different ways to configure the servo. However I decided the noise problem meant there had to be a better solution.