One decision that a person designing a new layout must consider is how he/she plans to uncouple cars on the railroad. Since the vast majority of model railroaders at this time use either Kadee couplers or a clone, I will discuss the two major ways of uncoupling them.
The first way is by the use of a magnet positioned underneath or between the rails. The couplers to be uncoupled are then stopped over the magnet, slack run in allowing the knuckles to move to opposite sides and allowing the engine to move one car away from the other. These magnets may either be of the permanent or electrical variety. The pro's of this method is that no one needs to reach into the layout to uncouple cars and risking the possibility of damage to either the railcars or the layout scenery. The con's of this system is that you are limited in where you can uncouple, i.e. no magnet no uncoupling, and if your train takes slack at the wrong place or stops with cars over a magnet you can get unscheduled uncoupling (can be avoided with electromagnets or movable magnets). The magnets will allow you to set you couplers for delay so that you can push a car to a desired spot, this will not work on a track with several spots that need to have cars not coupled together when properly spotted thereby requiring multiply magnets on a track.
If you are going to install magnets, it is best to decide where they will be needed early in the design stage or at least by the time of track construction as they will affect sub roadbed and roadbed. Location must considered, as placing a magnet closer than a car length to a curve can hinder uncoupling (possibly worse on curves bending to the left when coming off the straight section of track.
The second popular way to uncouple is with a manual aid such as a pick which may be as simple as:
- flat blade between the knuckles
- special tool between the knuckles
- pointed tool (skewer) between the knuckles
- rod from above to catch and move the "air hoses"
- Z rod from the side to move the "air hoses"
- two magnets (wands a la Rix) that can be lowered between next to the couplers.
The major pro of the pick system is that it allows for uncoupling at any location on the layout that can be reached. Many operators feel that this helps to simulate a brakeman working the cut lever on a real railcar. The con's are that reaching into the scene destroys the illusion of the model railroad, i.e. no large hand from the sky with large telephone pole uncouples on a real railroad, plus if not careful one can damage cars or scenery.
One thing that must be stated is that the use of either system is not exclusive; you can have both magnets and use a pick to uncouple cars. This will always be a matter of personal taste of the layout owner.