Lego Train Decoupling

I was perusing the EuroBricks Train Tech Forum and saw a topic on decoupling.  The OP was describing an HO scale decoupler, which was track based and worked quite well in separating the wagons/coaches/engines etc.

Now I’d seen previous solutions and they seemed to be highly engineered, on-board motorised devices which I wasn’t keen on as it used another motor.

Don’t get me wrong, I like these solutions and the ones for motorised switches, only if I had access to lots of motors...

So the question “Is there a simple decoupler design that can be built from relatively few bricks that works ?” is what I started to think about.

Being an AFOL, I have bits of half finished designs and other miscellaneous pieces on my desk, so I had a look at a bit of straight track and a couple of bogie assemblies.

The magnets which hold two wagons together are weak enough to be easily pulled apart without too much force so some type of lever to hold one in place whilst the other moved away seemed to be the way to go. Okay, now how do I get it on the track ?

A standard piece of straight track is made up of rails, sleepers and more importantly spaces. The rails are solid so you can’t slide anything underneath, and the clearance is maybe 3.5 plates high before it  will derail trains.  The sleepers take up one plate of that size, so you are limited to 2.5 plates to play with.

I was happy with the solution being some type of rod/lever which would stop the wagon and briefly thought of using Technic axles, but how would that connect together ?  I didn’t know so have filed that away for later.  So if axles weren’t viable, what next ?

It could only be a plate.  These were thin enough and were one solid piece which could be used to hold a wagon.  However, as there are studs on the sleepers, I can’t have the plate in the usual configuration, what about tiles ?  Tiles are the same, so they would need to be upside down, but then so could a plate.

The upside down plate is definitely the key, now the design was beginning to take shape, balancing the plate on the track I could now create a pivot.  So I added a 2 x 2 plate at one end and a slide shoe on the top.  This would catch the underside of the train and it would slide over it.  As this happens that end of the plate is pushed down, forcing the other end up to catch onto the following wagon. 

How long should the plate be ?  Too short and the plate wouldn’t pivot, so anything under 6 studs long would fail.  Long plates are also no good as they catch the passing train before it gets to the wagon that will be decoupled.  So 2 x 6 studs it is.

So I added a few tiles on the sleepers to hold it place.  Job done, time for a test.

The first clip shows two wagons rolling forward, with the second one separating itself from the first.

The second clip shows a train reversing a wagon over the decoupler, then moving forward to decouple.

Hey, it works, sweet, now where’s my plan for the time machine...?