Turnout Servo Control the easy inexpensive way...

Sumner Jul 14, 2020

  1. Sumner

    Sumner TrainBoard Member

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    I've been working on a way to control servos for turnouts and other uses that is inexpensive and doesn't require using an Arduino or expensive commercial servo controllers. If you know how to solder and have access to a 3D printer or can find someone who does for under $8.00 you can control servos for your turnouts or other simple uses.

    You can't control a servo with a simple on and off switch, you need a servo controller. Dave Bodnar came up with the idea of using a servo tester as a means of servo control. If you buy them in quantity you can find them for as little as $1.50 each. Add about another $4.00 to that for LED's, switches, a resistor, servo cables and a little wire and you have not just a servo controller but also a control box that can sit at the edge of the layout and that is used to throw the turnout and show which route is active.

    I'll be putting up more on this later and on my site with additional pictures and two simple wiring diagrams but for now here is what I've come up with.

    [​IMG]
    I picked up a 5 volt power supply for $15.00 that will power about any number of servos and controllers as they only draw current when a turnout is thrown. You run two power wires from the power supply to the control box. You could run a pair of wires around the layout from the power supply and tap into them where needed.

    [​IMG]

    From the control box to the servo controller and on to the servo itself you use inexpensive 3 wire servo cables that you can buy in different lengths and daisy chain together if needed.

    [​IMG]

    The control box (3D printed) contains 3 switches (one not shown inside the box), 2 LED's that show the chosen route and a resistor. I'll later post pictures of the wiring inside along with a wiring diagram. The wiring is simple and you can wire one up in under 10-15 minutes once you have done a couple.

    Also there are a number of different tops you can print that show a left or right-hand turnout facing different directions, curved turnouts and turnouts as you would see them in a yard ladder. You can place the box wherever it is needed or gang them together so as to represent the track plan. More pictures showing this later.

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    The above board is mounted out of the way but you mount it after you have installed the servo and turnout. You can use it to adjust how far the servo throws the points in either direction. This is helpful if you don't mount the servo exactly centered under the turnout. Also the servos will throw the points way to far if you don't have some means of controlling their throw. This way if you need a little more or less pressure on the points it is easy to set and can be adjusted easily in the future if needed. It will help for the differences needed in throw depending on scale and layout thickness under the turnout.

    I took Dave's wiring example and expanded on it a little by adding the second potentiometer (the 10 cent trim pot) to the circuit. This addition is what allows you to adjust the throw in both directions. Assembly consists of screwing the small board onto the 3D printed bracket and adding the trim pot to the bracket and soldering on two wires.

    This circuit is activated when you push the button on the control box at the edge of the layout. Another advantage to this is that the servo is not powered all the time, only when you throw the turnout. For this reason you don't need a large power supply.

    [​IMG]

    You use different length servo cables between the components. Above I had over 18 feet of cables daisy-chained together and it was still working fine. The servo controller can go under the layout as you only use it when you need to adjust the servo's throw on the points so normally you would have a shorter cable than shown between the control box and the servo controller.

    You could use the components for other items on the layout where you needed to move something with a servo and wanted to control the throw and when it happens.

    I'll post more info down the road but I do have the print files up for the servo bracket now...

    https://www.thingiverse.com/thing:4515776

    I'll soon have the files up to print the bracket for the servo controller and the control box with different tops.

    Sumner
     
    BNSF FAN and drbnc like this.

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