Introduction to model railways/More technical issues

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This page will discuss some of the more specific detailed issues commonly needing explanation

Understanding Track Code[edit | edit source]

Track is sold in sizes called "codes," which indicate the rail height in thousandths of an inch. Code 100 (.100"), code 83 (.083"), and code 70 (.070") are common sizes in 00/HO scale while code 80, code 70, and code 55 are used for N scale. These sizes represent the various sizes real railroads use.

Older rolling stock may have flange sizes that are greater then the rail height, meaning the stock will bump along the chairs (that attach rail to sleeper). This is not a Good Thing!

Sleeper Spacing[edit | edit source]

Track purchased in the UK is suitable for running H0 and 00 trains. The difference in scale is about 10%, and the track is scaled for H0 use. This means the sleepers are incorrectly positioned for use on an 00 model. Most modellers don’t worry about this, but it is possible to reposition the sleepers.

For the benefit of those of you respacing Peco Code 75 / 100 track, you need to be aiming at 5.5 mm between the sleepers - this gives a good balance between the narrow gauge track and small sleeper size, making everything look in proportion. A few things to bear in mind - 1) In the real world sleepers can be closer together on high speed lines, and curves. 2) Point timbers are closer together than plain track so it’s no big deal to have the points standard looking. 3) Wooden sleeper track will have a different spacing to concrete sleeper track. 4) Don’t worry if the sleepers aren’t perfect, it’ll make it look more prototypical. 5) Glue the track down - there’s no point in making it look good and then ruining it with track pins! 6) Use N Gauge ballast, again for a similar reason to the last point. 7) To make it look even better, remove all of the webbing, don’t just cut through it. It takes a lot longer but it looks much better when ballasted.

Point motor options[edit | edit source]

Points near Plymouth (England)

There are a number of ways to change/throw a point.

Manually - cheapest and easiest for points you can reach.

Use a long pointed stick. Slightly less intrusive than a direct “Hand of God”, but still not great although useful for points in hard to reach places that you fitted a while ago and can’t automate!

Manual Ground Throws. These are close-coupled to the point and are operated by hand. Note that in many circumstances this is prototypical as remote sidings often had manually operated throws, so these can look appropriate on a model railway.

Wire in Tube. Similar to a Bowden cable on a bike, and the same technology as used in RC airplanes. A thin wire down the inside of a narrow plastic tube (typically <1mm) engages with the point at one end, and with a ground throw or motor at the other. The tube can be buried in a groove in the board, hidden under ballast etc. This technique can be useful if you cannot get under a baseboard, but setting them up accurately can be tricky.

Solenoid motors. These used to be the standard motor for point operations. A coil of wire around a soft iron core is energised. The resulting magnetic field attracts the core, which is connected to point. Reversing the current reverses the polarity, and moves the point the other way.

Manufacturers make units that clip directly onto their points, which can then be wired via a switch to the AC auxiliary output of your controller. This provides a cheap and effective remote system. The downsides are that the operation is akin to “snap action” and can be noisy - this is very unlike the real thing. If you have a lot of points, you will need to improve your power supply by adding a CDU (Capacitor Discharge Unit) to increase the power available.

Some solenoids can be fitted below the baseboard and operate the point via a stiff rod that goes through the board and engages with a small hole in the point tie-bar.

Specialist point motors. These are fitted below the points, and operate the point via a flexible steel rod engaged with the tie bar. These motors operate at a slower speed and so are more prototypical, and can include auxiliary contacts to operate frog polarity switching, signals, lights etc. Due to their being fitted below board, consideration to fit must be made at the design and build stage.

Servo Motors. These are cheap devices and are as used in RC airplanes. They are controlled by a specialist circuit board, where the limits can be set-up as required. Servo motors are small and retrofitting is much easier than with underboard point motors, as they can be let down into the board at the side of the track. Fully hidden installation beneath the board is also possible.

Point Motors and Servos can be operated using an analog control panel, or can be addressed as part of a fully integrated DCC system.

Documentation[edit | edit source]

As you progress in your model, you will add more wires. These could be additional track feeds, lights, points, signals, animations and so on. Over time, you will forget what goes where! To aid future fault finding, make a note of your wiring details. Number the connectors, use different colour wires for different services (and stick to this!). The document can be as simple as a handwritten notebook, or a fully functioned database.

Examples of simple wiring list and point motor wiring diagram

Simple terminal strip detail for model railway


Couplers[edit | edit source]

Couplings are one of the unsung heroes of our model railway.

Obviously, they allow you to connect stock together, without which we only have individual wagons, and not a train! But what else do these components do? What Bad Things can happen when they are not properly set-up, and what fixes and alternatives are available?

Let’s think about uncoupling a bit more...your train has left the freight yard, you’ve traveled over 100 compressed miles, and now here you are ready to deliver a load of stuff to a widget factory. You’re backing into the spur and your “crew” is getting ready to uncouple the wagon so it can be left at the warehouse and unloaded. What happens next?...

Worst case scenario - two giant hands come down from the sky and try to jiggle the wagon loose from the rest of the train. It doesn’t come loose right away so the hands have to lift it off the track in order to unhook it, then try to rerail it again next to the furniture factory.

Next to the worst case scenario - one giant hand holding a big stick comes down from the sky and puts the stick down between the couplers; the big stick turns a little and the car rolls free.

Best case scenario - there are no hands in the sky. The train backs up into the spur and stops for a moment. The couplers separate. The train pulls forward a little, then backs up slowly, pushing the wagon into position next to the unloading dock. The train pulls forward with the spotted wagon remaining in place at the loading dock. The train then pulls out onto the mainline to travel to its next destination.

Different coupling designs

Tension-lock couplings.

The most common design used in the UK is the “tension-lock”. These are relatively simple devices, and have a small hook on each wagon that links over a receiving bar on the adjacent unit. When tension is applied (eg by the loco), they lock together - hence the name.

Problems with this design?

  • On tight radius bends, the buffers can clash and lock together causing derailment.
  • Shunting and positioning wagons is not easy, with decoupling devices not prototypical.
  • Manual decoupling of wagons often tricky.


This type of coupler is much more like a prototypical device, and some manufacturers offer a near-scale item. They are much easier to use in a shunting environment, with decoupling achieved by hidden magnets, or by magnets just above sleeper level. Kadee is the leading manufacturer of this type, offering a wide range of items with different lengths and heights allowing retrofitting to a large range of stock. A number of manufacturers claim to be equivalent to Kadee.

N Gauge Rapido tension lock.

Manufacturers in this scale have pretty much standardised on the rapido tension lock system, which looks a little more like a prototypical unit.

Horn-hook couplers.

Often found on older H0 (N American) models, these rely on side pressure to keep them locked

Chain and Hook.

This type is common on the larger scales and is prototypical for old stock. Modellers in Fine Scale (4mm) will also use this type of coupling. Remote uncoupling is not easy with this technology, although it can be attempted with remotely operated solenoids built into the rolling stock. Generally coupling/uncoupling is achieved by “Hand of God” using a stick with a small hook on the end to lift the chains into position.

Dingham autocouplers work with 3-link and are unobstrusive automatic couplers


Most people don’t like horn hook or tension lock couplers and can’t wait to replace them with (or “convert” them to) knuckle couplers that are more realistic and work well with the magnetic uncouplers. This allows the Best Case Scenario described above. It takes time and effort to convert all of your equipment to knuckle couplers, but you dont have to change everything, at least, not straightaway. Simply do the rear hook on the locomotive, and one hook on one wagon which will act as the lead wagon on the train. All the remaining hooks can remain as-is.

Coupler height

No matter what kind of train couplers you have, they won’t work well if they are mounted at the wrong height. You will need a coupler height gauge for your scale to tell whether your couplers are the right height or not.

Assuming the couplers are mounted on the wagon, if the coupler is sitting too high, you can lower it by putting a shim between the bottom of the wagon floor and the coupler pocket. If the coupler is too low, you can add one or more washers between the bogey/truck and the wagon bottom. If the coupler is mounted on the bogey, you may have to replace the bogey assembly or the wheels, particularly if the coupler is too low.

Magnetic uncouplers

Kadee was the first manufacturer to develop this system for knuckle couplers, in which a special magnet (not just any magnet) is positioned under the track at a strategic location like in front of a branch line, spur or ladder, such that, when a train is backed up and stopped with the knuckle coupler over the magnet, the “glad-hands” of the coupler come apart when slack is allowed. The train should then be pulled forward a little, and then backed up again to push the wagon(s) into the proper position without recoupling. The train can then pull out of the spur leaving the wagon where it was placed. This is called the “delayed uncoupler”, as opposed to the “regular uncoupler” which will recouple itself to the train after it is pushed back off the magnet.

Youtube has a number of videos which demonstrate the principle of magentic knuckle coupler operation. some videos also show how tension lock couplers can be converted for magnetic uncoupling

Electric uncouplers

These are also available for all scales, which are primarily electromagnets activated by applying current to a wire wrapped around a cylinder many times which creates a magnetic field. These have to be mounted in a space cut out from under the track.

Manual uncouplers for tension lock couplings can be fitted. The train must be positioned over the unit and the loco backed-up slightly to take the tension off the coupler. The uncoupling ramps are very obvious.

Uncoupler installation tips

If you are going to use uncoupling devices, it makes sense to include them in your original track planning. It’s easier to install them as you are laying your track initially rather than trying to do it later, although it can still be done. You may have to use a rotary tool or track saw to cut out and replace small sections of track in order to place the magnets, but it wouldn’t be that difficult. If your track is already laid and you want to install uncouplers, go for surface mounted magnets laid above the sleepers available from the manufacturer. Small rare-earth magnets can also be set into small (~4mm) holes drilled into the track-bed.

Incorrectly installed couplers can lead to derailments, or disconnections and subsequent crashes as your train hits the left behind wagon in the tunnel!

Read about full size w:Railway_couplings here

Using flexitrack[edit | edit source]

Flexitrack allows you to make bespoke curves and will give greater credibility to your model than using Setrack. The problem though is that as soon as you connect one end to a fixed track and start to bend it the rails shorten and lengthen with the end popping out of the connected fishplate. What's the correct way to use flexi track to avoid this?

Always pre-bend your track to the curvature you need. Fix one end really firm so the ends stay parallel - as you gradually introduce your curve at the other end you get different lengths, due to the different radius (and hence circumference of the circles you are making). These need to be trimmed square.

Once happy with the curve , you need to keep the new (irregular rail) firm and then cut the rails square. I hold with bull-nosed pliers and cut using a Dremel. Xuron cutters also work. Do NOT use regular side cutters as these pinch the rail and you will have a lot of filing and cleaning up to do which will probably pull the rail out of the chairs.

Note that if you do pull the rails out, with care it is possible to completely remove and re-thread rails on flexitrack!

The better curves you will get are well worth the practice and effort.

Forced perspective[edit | edit source]

Forced perspective is a technique which employs optical illusion to make an object appear farther away, closer, larger or smaller than it actually is. It manipulates human visual perception through the use of scaled objects and the correlation between them and the vantage point of the spectator or camera. In our miniature railway world, it is often used to make things at the back of the baseboard, which may be 24” to 36” away, to look as though they are much further away. This effect is used to good effect in the purchased backscenes, that are at a significantly different scale than objects at the front of the scene.

If your layout is on a board with viewing from every side, there is limited scope to apply the technique however wherever you have a “front” and a “back” to your model, there are various tricks you can employ.

  • Trees can be slightly smaller than the same “size” tree at the front
  • If you have picked up various model cars at sales put the smaller ones at the back
  • If you are making downloaded card buildings, print the ones for the back of the scene slightly smaller.
  • As mentioned, the backscene painting/picture can be scaled smaller
  • As shown by a couple of teams on the GMRC, you could build backscene models in a smaller scale (i.e. 00 at the front, N at the back)

You can read more about forced perspective here