Model Railroad Uncoupler Magnet Placement

There are two ways to achieve semi-automatic uncoupling. The first, as discussed in Delayed Action Tension Lock Uncoupling, allows for the locomotive to uncouple by simply changing direction, having passed over a magnet.


However, converting to Kadee style couplings can be expensive, and is not without it's own issues - see Adding Symoba NEM Pockets & Kadee Couplings. 


The alternative is based on a variation of the Brian Kirby magnetic uncoupling solution. This is a cheap, do-it-yourself addition to couplings that use a plastic tension locking hook (rather than the metallic Hornby ones) and allows for 'instant' uncoupling when positioned over a magnet.


Uncoupler Magnet Placement


In both cases, the placement of a magnet under the layout (or at least embedded in the base board) causes the decoupling to occur. The placement of the magnet tends to be fairly permanent, and as such needs careful thought.


For example, when delayed uncoupling is used, a rake can be spotted on any one of a number of sidings, even after passing over sets of points. But, when using immediate uncoupling, a magnet is needed for each individual siding.


This is explained more fully in the Kadee Inglenook Magnet Placement Advice article.


Another important consideration is for those who are planning an oval layout : every time the train runs over the magnet, the uncoupling action will take place. Depending on the rest of the track plan, this may, or may not, matter.


As a matter of course, though, it is usual not to place magnets underneath ovals, and reserve them for terminus operations (fiddle yard, terminus station, goods yard, etc.)


When Placement Doesn't Matter


In the Variations article, for those who haven't read it, there is at least one solution to the above - use an electromagnet. These can be switched on and off at will, and as such are widely used for selective immediate automatic semi-magnetic decoupling.


A final thought - there's often no need to put modified coupling in place on each piece of rolling stock. Commonly, though, they'll be fitted to locos and brake vans, as well as the start and end wagons in longer rakes.


However you choose to implement it on your layout, magnetic uncoupling can open a whole model rail experience!

Inglenook Kadee Magnet Placement Advice

Many of us, especially those of us with a shelf switching layout, have an Inglenook. Kadee magnet auto-coupling/decoupling makes operating an Inglenook much easier (when it works) but is a real pain when it doesn't, or if the magnets are put in the wrong place.


First off, what exactly is an Inglenook? Figure 1 shows the basic layout (adapted, with many thanks, from the Model Railways Shunting Puzzle Web Site) and can be adapted to any scale, with a couple of points (switches) and 7 or so bits of track.

Figure 1: Basic Inglenook

The operating fun to be had with the Inglenook relies on being able to pull wagons off trains (rakes) which are parked on the ends of the Inglenook, and swapping them with others, in a kind of Towers of Hanoi style puzzle.


While decoupling using the paintbrush-with-a-loop-of-wire-on-the-end solution is all well and good, for the ultimate in operating action, many enthusiasts like to implement some kind of automatic decoupling solution. Kadee manufacture such a solution, using magnets and knuckle couplers to provide a reliable shunting experience.


Due to the way that they work, on an Inglebook, Kadee magnet based auto-decouplers  are a great solution for one simple reason : delayed decoupling. For layouts using electromagnetic decoupling (in my opinion, the next best thing to Kadee's solution), magnets are needed at each place where a wagon (truck) can be uncoupled.


Wagons can be uncoupled  from other wagons, or from the loco (shunter), and Figure 2 shows where the placements should be (or could be) for an Inglenook using only electromagnetic automatic decoupling.

Figure 2: Inglenook Magnet Placement

There are other places that magnets might be appropriate or desirable, but Figure 2 serves to illustrate the point - 3 separate magnets, with three separate buttons, are required to be able to spot trucks (wagons) on each of the three sidings of the Inglenook. 


Kadee magnet based uncoupling changes this, as seen in Figure 3.

Figure 3: Inglenook Kadee Magnet Placement

The reason only a single magnet is required is that once decoupling has been activated the remaining rake (train, or wagon) can be shunted into place, and remains decoupled. When the loco pulls away, the decoupled wagon or rake is left in place - delayed decoupling.


There is a drawback, however. In order to decouple a relatively long rake, the track in front (to the left of) the magnet needs to be long enough to accommodate it. However, if this proves to be a problem, more magnets can be added on the sidings themselves, this allowing decoupling with some, or most, of the train over the points.