Home-built uncoupler

This appeared in Modelspoormagazine 68. More text and pictures can befound there...

Uncouplers are threated a bit off-side by the manufacturers. While a lot of effort goes into couplings themselves, uncouplers often have a poor realistic appearance. Therefore, I designed an alternative.

Most manifacturers have an uncoupler rail which more looks like a jumping car maintenance bridge. This concept, though efficient, isn't realistic-looking at all. When using short couplings, you can't but use a stationary uncoupler - unless one chooses to uncouple manualy. Home-built means in this case enterily home-built: even the solenoids are home-made. My acquired second-hand milling machine came in handy, especially since I made several uncouplers in one session.

Construction is fairly straightforward: a selve is the power source which pushes a metal core up, connected to small plate. To protect the solenoid against heating, some electronics are added to reduce power. A large common electolytic capacitor holds the energy, which is released by a power transistor on each uncoupler.

I made a small mold from some scrap pertinax and a few nuts and bolts. The heat-resistant material was cut in shape to hold two brass M6 washers. A 30mm long piece of 6mm brass tube is shoved through these washers. With this mould, several constructions can be made fairly quick. A bit of soldering fluid makes construction quite simple.

The mould holds everything in place while soldering. Enough heating power (at least 50 Watts) is needed. The result is a bit rough, while we need a very smooth surface to continue making a solenoid. This will be corrected in the next steps.

A milling amchine is very useful for this job. At a rather slow speed, I gently cut off a piece of the outside washer, together with part of the tubing. Any scrap material is drilled off.

On milling the centre piece, it's important to do this in small amounts, as the brass can be bent easily. the result is a smooth body with straight edges. All that's left is to drill a tiny hole through the outside washer to hold the start of the wire.

Thin 0,15mm insulated copper wire is put through this little hole. We can now start filling the solenoid core. At very low milling speed, guide the wire from left to right and back until the whole core is filled evenly.Cut of the connecting wires with some 5cm spare length.

The core of the electromagnet is milled from an iron rod. Get its diameter just a bit smaller than the brass tube's inside, so the iron core can slide through smoothly. A small pin is milled at one end. This way, several cores kan be made at once.

To prevent the core from turning round in the tube, a gap is cut. This can be done by hand, but a small saw blade, placed in our milling machine gives a far better, more precise cut.

The electromagnet's core is now ready and should look like the one in the picture. We now need a non-magnetic part to extend the length. A plastic (styrene) rod of the same diameter is placed in our milling machine.

After milling the styrene rod to the right diameter, a hole is drilled at one end.This hole will hold the iron core pin. Milling styrene should be done at low speed, as it can easily melt.

After finishing the core - both iron and styrene - we can do some testing. The electromagnet's wires are connected to a power source, and we can check if the milled two-component core responds to the electromagnetic field of our home-made magnet.

A 2mm thick styrene sheet is cut and drilled in shape, so it holds our home-made magnet. A drop of cyanoacrylate glue secures the magnet.

A piece of 1mm styrene sheet, cut in shape shall be placed in the middle of the 2mm thick piece. It will hold the magnet core in its chosen position. A scrap piece of thin sheet brass is cut and drilled in shape to form a heat-sink for the power transistor.

The transistor's legs are bent to the right shape. An M3 bolt and nut, with some heat-conducting fluid applied, holds thetransistor firmly against the home-built heatsink.

A three-poled connector povides access to the "outside world". A bit of glue is applied to secure this. After gluing, the resistor and the other leads can be put in place and soldered.

Now this part can be mountedto the bottom part, and the solenoids' connections can be soldered. Test the setup at his stage. Especially the insulated solenoids' wires can cause a problem.

We can now prepare the layout tracks for our home-built uncoupler. A 7mm-wide hole is drilled in the rail's center.

Some small wood screws secures our mechanism against the layout's subroadbed. We can now connect the uncouplers to the power source. Notice the power buffering capacitor with its charging resistor.

If you have precisily measured the subroadbed's thickness, the top of the styrene core part should be at the exact height. Otherwise, some more milling is due.

The moving part of our uncoupler should be disguised. A railroad worker's path is a convenient camouflage. A piece of 1mm-thick styrene is therefore cut in shape, painted and wheathered.

A 0,5mm thin piece of styrene is glued to the styrene core part of our magnet. Once put in place, it will be a basis for the camouflage part. The bottom side of this should be painted black.

When completing the pathway, you should carefully watch its position. We wouldn't want to cause trouble to moving trains, do we?