Article by Sal Ciofani

I have been using Kadee O-Scale knuckle couplers for almost ten years.  Because they are designed for traditional model trains, in order to connect them to LEGO trains, I had to literally bolt them on to Plate, Modified 3 x 2 with hole.  So when I heard Brick Model Railroader announced they were releasing Kadee couplers with custom molded, LEGO compatible draft gear boxes, I was very intrigued.

From the beginning, one of the great advantages offered by Kadee’s couplers, besides the realistic look, is the ability to automatically uncouple cars and engines by use of magnets.  This makes realistic switching operations in rail yards or at industries, without the “Hand of God” pulling cars apart, more realistic and enjoyable.  There are a variety of ways to uncouple cars equipped with Kadee knuckle coupler from uncoupling “pics”, permanent magnet uncouplers, and electromagnet uncouplers.  In traditional model railroading the most popular and simplest way to uncouple cars is with an uncoupling “pic”.  Kadee sells #241 Dual Tool – Manual Uncoupling Tool & Built In Spring Pic, any pointed object, such as the LEGO Spear 93789 or a sharpened pencil will work.  I personally use a Wooden Manicure stick, I prefer the type with a flat tip.  To uncouple cars simply insert the “pic” of your choice between the knuckles of cars and twist counterclockwise to open the couplers and push them to the side.  While holding the couplers open with the “pic”, pull the rest of the train away from the car being left.

Kadee couplers are equipped with curved a metallic air hose detail that doubles as the coupler trip pin.  The magnet attracts the trip pin and moves the trip pin to the side, opening the knuckle and allowing the cars to uncouple.

With the couplers positioned over the magnets mounted under the track, the magnets move the couplers to the open position.  The locomotive (left) can now pull away from the car (right) leaving the car over the magnet.

While the coupler is over the uncoupling magnet, the magnet will hold the coupler in the delayed position, knuckle fully open and coupler pulled to the knuckle side of the car.  When to adjacent couplers are in the delayed position, the locomotive can shove the car to the desired spot.

With the couplers still positioned over magnets, the couplers are held in the delayed position.

The locomotive can now shove the car into it’s final position to be left without the couplers recoupling. 

The couplers will fully uncouple when slack is allowed in the joint between the two couplers.  To avoid this when retrieving a car that has been left beyond the magnet, or otherwise passing over the magnet when uncoupling is not desired, it is important to maintain tension when pulling, or compression when shoving a train over the uncoupling magnet.  

The couplers in the open position remain connected when the connection remains under tension with the locomotive steadily pulling on the train.

The couplers in the open position remain connected when the connection remains under compression with the locomotive steadily shoving on the train.

To ensure the magnet can adequately attract and move the trip pin to fully open the coupler, the trip pin must be adjusted as close to the magnet surface as possible, without interfering with between track obstructions like grade crossings or switch tracks.  This is relatively simple to do with a gentle squeeze of Kadee #237 Coupler Trip Pin Pliers – For HOn3, HO, S, On3 & O Scale Couplers, needle nose pliers can also be used, although that method requires twisting the pliers to affect the appropriate bend.

Using the Kadee #237 pliers to bend the coupler trip pin down.

Using the  Kadee #237 pliers to bend the coupler trip pin up.

To facilitate ensuring proper adjustment of trip pins, I have made a simple modification to BMR’s coupler height gauge.  

To add a trip pin gauge I removed the bottom plate (shown above the coupler gauge) and added the parts shown below the coupler gauge.

BMP Coupler Height Gauge with added trip pin gauge.  Note the coupler on the right has the trip pin adjusted to work best with uncoupling magnets, the left coupler’s trip pin is shown as it comes.   

The modified BMR Coupler Height Gauge in use.  The trip pin gauge helps to adjust the coupler’s trip pin is as low as possible while ensuring the trip pin is high enough to clear obstructions between the rails, such as switches and grade crossings.  

For those who want a more hands free or automatic way of uncoupling their railcars, there are a number of ways to accomplish this with magnets, between the rails magnets, under track magnets, and electromagnets.  The first magnet I tried was Kadee #308 Under-the-Track Hidden Delayed-Action Magnetic Uncoupler – HO, S, On3, On30, O Scale.  The magnet is slightly wider than the 4 stud track gage of LEGO track.  I cut the magnet and intensifier plate down to four studs wide to fit between the rails while leaving enough clearance for the LEGO train wheels to pass without causing derailments.  I removed a fraction of an inch from either side of the magnet to keep the polarity even.  In order to allow the magnet and intensifier plate to fit flush with the top of the rail of a LEGO R/C straight track, I needed to shave off and file the studs on one of the ties.  I then super glued the intensifier plate to the studless tie and placed the magnet atop the plate.  This magnet worked well, although, I was not completely satisfied with the look of a large magnet mounted between the rails.  

As the name implies, Kadee’s #308 Under-the-Track Hidden Delayed-Action Magnetic Uncoupler – HO, S, ON3, ON30, O Scale, is intended to be mounted under the track.  For larger scales (O scale and bigger) Kadee recommends stacking the magnets with a single intensifier plate.  I tried stacking several magnets atop an intensifier plate, six in total, with no real success.  The stack of 6 magnets is as tall as a section of track on a standard MILS base, making it impractical to incorporate into a MILS module without increasing the height of the MILS module.

I stacked six Kadee #308 Under-the-Track Hidden Delayed-Action Magnetic Uncoupler – HO, S, On3, On30, O Scale.   Not only is the stack too tall to fit within a MILS module, they six magnets did not have enough pulling power to activate the coupler’s trip pin.

During the Brickworld Virtual Halloween show, the suggestion was made to try Kadee #809 O Scale 3 Rail Between-the-Rails Delayed-Action Magnetic Uncoupler.  The package includes four skinny magnets that are stacked 2×2 and placed on an intensifier plate near each rail.  This method provided great results but requires a deep area between the rails to accommodate the thickness of the double stacked magnets.  This means standard LEGO track will not work, or will have to have ties removed from between the rails.  I had some Me Models rails that I used during my testing, which would be an ideal solution, if they were available.  The area at either end and between the magnets could likely be filled with LEGO ballasting to help blend the uncoupling track section in with the surrounding track.

Kadee also offers  Kadee #810 O Scale Thru-the-Ties Delayed-Action Electric Uncoupler Kit, which is an electro magnet kit to allow the user to electronically control when the magnet is active to uncouple cars.  This would be useful for installing the uncoupler in mainline locations and other areas where accidental uncoupling would be problematic.  I have not had any experience personally with electromagnetic uncoupling.  Electromagnets will require a power source, and a button or switch to activate them. 

Neodymium magnets were also suggested during the Brickworld Virtual Halloween show.  I selected K & J Magnetics BX884 1 1/2″ x 1/2″ x 1/4″ thick Neodymium Block Magnets.  BINGO!  I ordered four of the BX884 magnets and stacked them 2×2 and placed them 4 studs apart underneath a section of ballasted track.  The magnets are just shy of 5 studs long and about 1.5 studs wide.  I used 2x bricks between and at either end of the magnets, and snot bricks with 1x tiles on the outside to prevent the magnets from moving around.  With one plate of ballast between the bottom of the LEGO track piece, and the top of the magnets, I placed tiles on the baseplate where the magnets would sit.  I added plates as necessary to complete the boxes to securely hold the magnets in position. 

It took a bit of checking to make sure I had the magnet polarities oriented correctly to properly open the BMR Kadee couplers.  To correct the polarities only requires flipping one, or both, stacks of magnets over so the correct polarity is pointed up, being careful not to let the one stack from attracting the other.  Neodymium magnets a very powerful, the BX884 magnets have a pulling force of 26.2 pounds each.  They can be quite difficult to pull apart, and can attract each other from a fair distance.   It can hurt getting a finger or skin pinched between two neodymium magnets, and they can break if they come together with too much force.

Once assembled, the results are fantastic!  The BX884 magnets operate the BMR Kadee couplers smoothly and reliably, even under one plate, LEGO Track with filled in tie spaces, and 1×4 tie tiles.  The double stacked magnets also fit easily within a standard MILS module concealing them from view.  

The K & J Magnetics BX884 1 1/2″ x 1/2″ x 1/4″ thick Neodymium Block Magnets will be my magnet of choice for uncoupling magnets in my layout.  I plan to incorporate at least one of these BX884 uncouplers into my current LGMS module and have it available for people to try out at shows, such as Brickworld Chicago, Brickworld Milwaukee, and Trainfest.