Using a Servo and Servo Tester for Turnout Control

Sumner Nov 7, 2019

  1. Sumner

    Sumner TrainBoard Member

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    Just added a page on using servos, mounting them and a servo tester for turnout control.

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    The servo mount is close to others I've seen but has a pretty convenient way of mounting a limit switch to power the frog where it is easy to adjust the limit switch's position in relation to the servo.

    I found Dave Bodnar's excellent resource ...

    http://www.trainelectronics.com/Servo-simple-controller/

    ... on using a cheap servo tester as a means to control a servo a while back...

    [​IMG]

    I modified the wiring some so that you also can see how the turnout is thrown and have a little more control over the servo's movement.

    [​IMG]

    Above is a test of the wiring using a small panel and a 5v powered breadboard which allowed me to try different value resistors to see how they effected the throw of the turnout. I'll be using a 10 cent trimmer pot though instead of a fixed resistor in the next version.

    [​IMG]

    A big plus for this is that you can put it all together for about $5.00. That includes the servo and the parts needed to control it and also the LED's that will show you the selected route. Once mounted you have a lot of control over how much the servo moves the points and the pressure on them.

    More info and pictures here...

    http://1fatgmc.com/RailRoad/Trackwork/page-7.html

    If you make your own turnouts via FastTrack or other means you can have a powered turnout with edge of layout control for as little as $10 each,

    Sumner
     
  2. tracktoo

    tracktoo TrainBoard Member

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    Very nice method for remote turnouts. One suggestion that might help to keep the switch modification wiring a little neater is shown in these pics.

    Because I wouldn't be using three servos at once I cut out the board end of the three plug contacts for the top servo plug. Bottom is cut as close to flush as I could get it and the top is snipped right after the bend. One of the contacts is removed as only two are needed for the modification. I then soldered two wires (stripped bare) from the pot negative and wiper lugs to the remaining two pins. This makes all of the boards standard and the same style of plug can be used for the installation of the switch wiring instead of soldering leads.

    servo board mod 2.jpg servo board mod 1.jpg
     
  3. Sumner

    Sumner TrainBoard Member

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    Are you using the controller stand alone to control the switch points by turning the knob one way or the other?

    I ask as in Dave's method, which I pretty much used, you have either a fixed resistor or a trim resistor on the wiper contact on the pot and I don't see that in your example and you don't touch the knob once you first set it using a toggle switch to throw the switch.

    I'll be using a trim resistor to set the throw distance and the the pot to set the points to one side before they are thrown. I want a little more flexibility since I'm building the turnouts and they aren't quite as consistent as commercial ones in the throw distance and/or the pressure you want to put on the points when thrown.

    I want to have the servo controller and the trim pot down a little further behind the fascia and the toggle switch, push button switch and LED's higher and will need to run three wires between the two locations so using the 3 pins on the controller as you have done intrigues me as I could then use servo wire between the two points and that would make things neater. I'll add pictures and a wiring schematic later when I do this as we are out of town now. So thanks for the idea,

    Sumner
     
  4. tracktoo

    tracktoo TrainBoard Member

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    I am using the same basic set-up, resistor (10K trim pot) and switch, as originally described. All the pictured mod accomplishes is to afford a neater, easier method of attaching those devices to the board. The mods can be made on the bench and then all future attachments made under the layout are just plugging it in.

    Let me add for clarification as I thought that no description, the original from Dave Bodnar or this one, made clear that the added resistor (or added pot setting) sets the span and that the board's original pot will move that span to a new zero by adjusting the original pot. Another way to say it, once a span (travel) setting is accomplished with either an added fixed resistor or adjustable pot, turning the board's pot will move that travel amount further CW or CCW. To change the travel amount the resistor value would need to change. This is an argument for using a trim pot in lieu of a fixed resistor.
     
  5. Sumner

    Sumner TrainBoard Member

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    Thanks for the update. I think we are both on the same page and thanks again for the idea of using those pins,

    Sumner
     

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