# Securing servo mounts under layout to plywood



## videobruce (Jun 15, 2011)

I'm not new to model railroads, but only to using servos to throw turnouts. Here is the situation:

N scale (thou HO scale applies here also, same servo & mount would be used), Peco electrofrog turnouts (around 57 yard & main), Motrak servo mounts, SG90 type servos, 3/8" plywood, 1/2 foam board, cork roadbed. Holes drilled under the throw rods, but they maybe too small and all are not 'dead center'.

The only two ways I can think of are screws by pre-drilling or hot glue, both with substantial disadvantages;

*Screws*; they need to be drilled first after marking the EXACT location of the holes. Self taping screws don't make holes in plywood w/o a lot of pressure which will not work here.
*Hot glue*; concerned about when it oozes out and/or gets on your fingers and sliding the mount around to position it if the glue setups too soon.

I tried looking around for small self drilling screws, but couldn't find anything. My concern for the hot glue other then above is the setup time after you apply the glue to the underside of the mount and tiring to line up the piano wire thru the hole on the base AND the hole on the 'horn'.

I also thought about double stick tape, but I can't see it sticking to typical rough surface plywood.


----------



## mesenteria (Oct 29, 2015)

Center the throwbar. Tape it in place, or use small brads/track nails to secure it in place...you don't want it to budge.

If you can center the mechanism's throwing pin, do that. If not, remember which way the pin must move once you fix the mechanism into place under the plywood.

Place tape on the flanges of the mechanism, where screws would go, leaving half the tape open, or free, to press onto the nether surface of the plywood.

Get under there, and line up the pin with the throwbar, inserting the tip into the small hole. Lift the mechanism into place, keeping in mind where the pin must move next, and secure it with the tape. 

Take your drill with small bit, drill where you must, and without disturbing anything, no tape removal, drive in the screws.

When you get up top, and remove tape or track nails, you should be able to swing the mechanism and move the throwbar.


----------



## OilValleyRy (Oct 3, 2021)

I would drill a small hole on the center line. Measure the distance between the screw holes on the mounting bracket. Divide by 2. Then you know where the screw holes need to be marked & drilled. Before mounting it, open up that center line hole with a larger bit. 
That’s what I would try. The only trick is knowing the angle of the track. I suppose that could be determined by making pinholes also on the center line about 4 or 5 ties away. Then along that bracket between the screw hole marks and pinhole marks and you’d get exact position and alignment every time. In theory.


----------



## videobruce (Jun 15, 2011)

*mesenteria;*
These are Peco electrofrogs with the spring. The points are not free to move to center. It's either normal or reverse.
I'm thinking pof using a empty servo mount as a template to mark the holes w/ the piano wire thru it. I plan on running that wire down from the throw bar instead of the other way from the horn against gravity.


----------



## mesenteria (Oct 29, 2015)

The springs can normally be removed from the throwbars of turnouts that have them, regardless of brand.


----------



## CTValleyRR (Jul 26, 2014)

So I have been using Tam Valley Depot servos for about 10 years now. They also use the SG90. Here are some things I have done and learned that may help.

1) Remove any springs from the turnout. You absolutely MUST be able to approximately center the points during installation to get the proper driving force from the servo driver. TVD directions are very clear on that point. The music wire from the servo provides the force to hold the points in place.

2) You require a 3/8" hole directly under your turnout points. You won't notice it after the turnout is installed. Deeper foam bases may require a slightly larger hole.

3) Exact alignment of the servo's axis of motion perpendicular to the track is not necessary. This is like horseshoes, hand grenades and nuclear warfare: pretty close is good enough.

4) Threading the needle: you can spend an eternity "fishing" for that tiny hole in the throwbar. Here is a better way: get a thin piece of brass tubing with an ID that just fits the music wire. You need about 8", longer isn't bad. Drill out the hole in the throwbar a little if necessary to accommodate the tube. It's easier if you have an assistant topside to hold the tube vertical, but you can also drill a piece of strip styrene to make "arms" that will hold the tube vertical and keep it from dropping through the table. I did this with a piece of styrene that just fit in the rail gauge; so it also serves to hold the points centered during installation. Again, vertical perfection is not necessary. You can eyeball it. Feed the tube down through the turnout, insert the music wire, mount the servo (see below). Pull out tube. Time: 30 seconds per turnout.

5) Mounting: the TVD servos come with an L shaped microplywood mounting bracket. I'm assuming you have something similar. Mark a reference line on the underside of the layout showing the approximate location of the centerline of the track above. Make sure the mounting area and 3/8 hole are clear of debris/ dust (sawdust / wood chips from drilling usually). Put a small piece of two sided foam tape on top of the bracket, thread the music wire through the brass tube, align the servo perpendicular to your track line (again, by eye is close enough), and press the double sided tape onto the underside of your layout. Pull out the brass threading tube and test the operation. Tweak the servos alignment if necessary. The double sided tape doesn't work for a permanent mount, but it will hold long enough to test and "permanently" affix the servo. If you want to use screws, at this point, pre-drill your layout base through the servo mounting holes (GET THIS RIGHT -- an off center screw can torque your servo out of alignment. Don't ask how I know this.... Do not over tighten the screws, again because of torque throwing off your alignment.

6) Alternate mounting method: I use this because I use a foam base that won't take screws, but I first tried it on plywood due to screw alignment issues, and it worked fine. Simply run a bead or fillet of hot glue around the edge of the servo mount, applying minimal glue to the area where the activating wire passes through. Believe me, this will hold everything in place. You don't want to drive the servo too far past the throw of the points anyway, so the amount of force on the mount is not great.

Sorry that's so long. Hope it helps!


----------



## videobruce (Jun 15, 2011)

Sorry for the late reply, I wound up using "Alien Tape" to secure the Motrak mount to the primed plywood. The test to it's strength is the fact I did have too remove and reposition many of the mounts due to the 'buzz' problem and the only way I could do that is to use a putty blade/scrapper since the holding property is what they advertised. One really has to 'pry' the tape off the wood to remove the mount! Clearly the weak point is the sole screw holding the servo to the mount.

I can't imagine using screws to hole the mount to the plywood. If you find you are 'off' and get the 'buzz', good luck drilling 2 more holes 1 or 2 MM away from the original.

AFA threading a needle with the piano wire, to my surprise, I had little problem finding the hole thru the mount (pviot point) and just a little more of a problem finding the 3rd hole from the end of the 'horn'.


----------



## videobruce (Jun 15, 2011)

I did retain the springs on the Peco turnouts as I have read possible contact problems for their 'electrofrog'. I do like to hear the 'snap' of the points, that lets me know the points are actually over. 
The exception was only a few troublesome servos that I had to disconnect the spring much to my dismay.


----------

