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My Little Railroad Buddy

Servo Motor Turnout Control - Servos

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I'm like a kid in a candy store when I find something new and a few months ago that was DCC servo motor turnout control.

What initially peeked my interest was the Anemodel Smart Switch. A recent article in Model Railroad Hobbyist - R/C Servos for Model Railroading - July 2009 convinced me to take the plunge. I bought a Tam Valley Singlet servo decoder (my review), a pair of Team Digital SMC4s, and 14 servos (two 9g servos and twelve 3.7g servos.)

Tortoise motor, 9g servo and 3.7g servo.

The size is much smaller than a Tortoise, yet these little guys have no trouble throwing a switch. And like a Tortoise, they require an adequate hole be drilled through the sub-roadbed. They can be mounted vertically, but I opted for the easiest method which is horizontal with just a little strip of double sided foam tape.

Servos installed with double sided foam tape.

Whats missing is a lack of contacts. The tortoise has DPDT contacts, making it easy to route frog power and to provide turnout position feedback. I'm willing to give up feedback on a lot of my switches, but I cannot live without frog power.

To route frog power, I tried four different kinds of SPDT micro-switches before I finally realized a 3.7g servo just does not have enough torque to throw a micro-switch. Unfortunately, I just bought a dozen 3.7g switches and I wanted to figure out a way to make them work. So I tried to make my own contacts.

Servo with homemade SPDT contacts.

The most reliable contacts was a three position circuit board I bought at Fry's. The steel throw wire was used to make contact between the common and polar positions. This was the most reliable method of those I tried, but was expensive, time consuming and finicky to get the throw arm positioned just right.

A 9g servo has plenty of torque to do the job and I decided to exploit this with the one working 9g servo I have.

9g servo with SPDT micro switch to route frog power.

Even though I couldn't use a micro-switch with all of my 3.7g servos, the Team Digital SMC4 has four stall motor outputs which can also be used to drive relays. I used this option to route frog power to my 3.7g servos.

So far I've installed 5 servos and I really like them. From here on out, I'll only buy 9g or larger servos.

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  1. gregamer's Avatar
    Also see my review of

    Team Digital SMC4 Servo Decoder
  2. gregamer's Avatar
    I thought the stick on micro-switch was going to be a good solution but it kept falling off.

    I also thought the Frog Relay Board

    I built for use with my SMC4 would be a great solution to my frog power problems, but It doesn't seem to be working reliably and I don't know if it's because the relays are no good, my wiring is wrong, or what.

    Also, I'm suspecting these servos are draining power from my DCC bus.


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