Sunday, April 20, 2014

Servo Turnout Motors On Foam Layout Boards

I have been fascinated by the use of radio-control-style servo motors to control the turnouts on the layout; but so far I have been having trouble deciding on the best way to go. The control products, and SwitchWright by Tam Valley Depot ( were leading the pack, especially when combined with a frog juicer to automatically route the power to the frogs (one practically “need to have” with hand-laid, Micro-Engineering, Shinohara, and Atlas Code 55 turnouts). The  SmartSwitch by ANE Model ( gave me just enough doubt to not rush in, and I recently stumbled across Iowa Scaled Engineering ( almost by accident, and have actually gotten one in to try it out!

The product that caught my attention:

MRServo-3: Slow Motion Switch Machine with PowerFrog Technology

"MRServo is a low-cost, low-profile, slow motion model railroad switch machine featuring PowerFrog technology. Using inexpensive and small RC servos, MRServo provides a cost-effective way to add slow-motion turnouts to your layout. PowerFrog technology provides a reliable, short-proof way to route power to solid frog turnouts. (Examples: handlaid, Peco Electrofrog™, Shinohara™, and Walthers™ models.) These turnouts will create a short if the points make contact with the opposing rail before the contacts driving the frog switch polarity. Traditionally, the solution has been to add additional gaps in the point rails, isolating just the frog. With PowerFrog, this is no longer necessary. When MRServo starts to throw the points, it momentarily isolates the frog. Once the servo completes throwing the points, it sets the direction relay to the correct polarity and, after a small delay, re-energizes the frog."

All well and good. But one thing that has yet to be answered through any of my “intense planning” (a fancy name for procrastination) is: “how to mount the servo on a foam-board layout?”. I searched the web for many weeks, but every example is either hard board or plywood roadbed. I have tried the Peco twin coil motor with a auxiliary contact unit, but as the motor is twice the width of an N Scale turnout, AND mounts directly to the turnout itself, I had two issues:

  • The size of the installation would not work for the most-crowded locations on the layout. Here is one example where I would like to use the powered turnouts, but would have severe trouble mounting the motors because of their size:

  • The mounting method, with the motor fixed to the turnout itself, did not leave me very happy. Part of the aesthetic drive in me could not accept the visibly obvious mounting, even when covered by a piece of card. The left-most turnout in this picture is one of two examples:

Having toyed with the idea of adding a firmer covering between the motor and the turnout, and continuing the cork sub-roadbed (while I don’t go crazy ballasting around turnouts, I do try to make it look like I have when possible) to maintain the appearance.

Solution found in other projects:

In a couple of places I have used foam-core board to solve clearance problems. The board is fairly sturdy when supported adequately, and does not warp or swell with the changes of the weather. A slight downside is the fact that the board is covered with card, and while it is water resistant, it is not completely waterproof. I would recommend sealing the board prior to applying scenery using water-based adhesives.

Another option would be to use a piece of Masonite, but the advantage in greater rigidity would not offset the ease of working with the foam-core. If for any reason I find the foam-core inadequate, I can easily change to the Masonite mounting using the same methods I will describe here.

Planning the installation:

I used the turnout planning products available on Peco's website ( to determine how much space I had to work with especially considering the crowded arrangements in a few places.

As the Circuitron Tortoise and Peco motors both have a significant footprint, and extend under the adjacent track areas, a “better” solution must allow use under the crowded parallel tracks. Alternating the smaller servo motor’s placement (left or right of the center-line, or towards the frog or away from it) would allow for closer spacing, and only a few places would require careful planning. Based on the spacing between the tracks, I settled on a one-inch by two-inch sized panel for the smallest installation. I proceeded on the assumption that scaling up to a larger panel would not add problems, and a successful test on the smallest size would be conclusive for all.

Changes to "Normal" mounting plan:

One of the advantages for the size of the servo was that it is not much wider than the track itself, so if the servo could be mounted on its edge, a much closer mounting could be possible. But to do so would mean making changes to the unit itself, and again, if it worked, great, but if not (and I find I have been making a mistake!), I could still mount it in the “traditional” side-mounting method.

Using a razor saw and file, I trimmed the original mounting lugs from one side of the case. To achieve as smooth a surface for the mounting tape as possible, I used a very fine emery board to smooth the cut marks in the plastic case.

The placement mock-up would theoretically work, so I proceeded with the plan to mount this unit as shown below:


Using the board to mount the motor in the foam board requires a hole to be cut; cutting the hole with a lip to hold the assembly level and at the same level as the top of the foam will reduce the visual impact and make the mounting much firmer. The nature of the assembly allows for a greater degree of flexibility in how to do so, allowing the profile of the surrounding track to be carried through the mount. So far, only the servo option offers the reliability to mount the assembly in such a manner.

The mounting hole is cut large enough to allow the motor to sit below the track level, with an adequate lip to support the mounting board:

I cut the hole using a disposable knife, which allows the blade to be extended and trimmed for renewed sharpness. The length of the blade allows cutting completely through the foam, and using the entire long, sharp edge to make the cuts.

Once the hole is completed, I used an X-acto knife to cut the lip for the mounting board. Trace around the edges of the mounting board with the X-acto knife, to ensure the hole is no larger than it needs to be. Make horizontal cuts up to the edges of the mounting board’s dimension. On a larger installation you could use a piece of the mounting board as a spacing gauge, but I used small cuts to make gain the desired depth, testing occasionally to ensure I did not go too deep.

The end result:

Test fit the mounting board into the hole, and verify the depth is only as deep as needed.

Track preparation:

With the mounting board in place, I fastened the cork sub-roadbed. In this installation the cork was installed in one section. I applied glue (PVA, or polyvinyl acetate), ensuring that the gap between the mounting board and the foam is kept free of the glue. I used the same plastic topped push pins I use for track laying to secure the cork while the glue dried:

This example shows the sub-roadbed for the turnout, illustrating how I prefer to add the diverging route:

I use a full strip for the primary direction (which may be the diverging route) and add the second strip to the other. This way the primary route has the most solid base.

Once the glue has dried, I used an X-acto knife to cut the cork on the sides of the mounting board, and remove the board:

The Peco turnout does not have a hole in the throw bar for the piano wire to go through, so I carefully drilled a 1 mm hole centered between the point rails. I cut the hole for the throw wire by using a small drill bit to open a hole centered on the turnout. Then, I used an X-acto knife to enlarge it, to allow the steel wire to move freely side-to-side:

From this point I followed the standard instructions, securing the motor in place below the turnout.

First, I mounted the board with the motor installed, testing that the throw wire moved freely from side-to-side before the glue dried.

When I laid the track, I also glued the turnout in place with PVA, avoiding any moving parts. The throw wire has more than adequate travel to compensate for any shifting or required variation form the plan, and allow proper operation.

Should the motor ever require replacement, the foam board and foam-core board are easy enough to cut through to cut the current installation out and make new cuts to mount a replacement motor (or remount the original one), but using a completely new mounting board.

Once everything is dry I connect the power and try it out. The example shown is an Insulfrog turnout (it’s a long story…), so I did not test the power routing. This was purely an exercise to validate the mechanical aspects of the project. I’ll post a follow up, and maybe a video, of it in action.


  1. Hi Dennis
    interesting kind of mounting your switch motor :-)
    Did you install your switches like this on your layout?
    What are your experiences?
    Greetings from Switzerland
    Starting in 2018 with his third layout :-)

    1. Hi George,

      Yes, I have actually been using this method on two layouts, with Peco, Micro-Engineering, and hand built turnouts.

      You can see the progress on other blogs, which I do continue to update: - primarily the use of servo motors, and at present, primarily on foam layout bases. I will be retro-fitting other turnouts with servos on more traditional wood bases. - a large loft/attic layout with crowded turnouts all built on foam base.

      So far I have not found any issues in this method, though the scenec treatment must consider leaks (so I prepare ahead of this) and too much water-based on the paper covering could cause an issue, but I have not found this to happen.

      I have also relocated a few turnouts and motors, and found this very easy as well.

      If you decide to have a go, feel free to post questions to me directly.

      Thanks for looking!