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Greetings, Train Tech! About a year ago, I posted my Umbauwagen 4yg. Here is the 3-axle variant, the 3yg: The name Umbauwagen means "rebuilt coach" -- these coaches were built after World War 2 by modernizing prewar compartment coaches. More accurately, this is an AB3yg (first/second class) + B3yg (second class) pair -- these cars were nearly always found in close-coupled pairs. A few survive as single units in work trains, painted yellow. The body of the model is essentially constructed the same way as my 4yg model: studs-up construction for the main body (leveraging the train window and the 2x8x2 curved slope), SNOT construction for the doors, the details around the buffer, steps, and corridor bellows. Of course I designed new side frames, and there are a few minor details that are different such as the lights above the end doors of the pair. These cars were painted green in DB service, but as the train window does not come in green I elected to build the 3yg in a different color scheme. I believe that this livery corresponds to 3yg cars used as trailers for the ET 85 electric units -- someone with more knowledge of German railways may be able to shed more light on this. At the time I built the 4yg I also built some test models to research how feasible it would be to build the three-axle variant. However, I ran into difficulties designing the chassis and moved on building the 4-axle variant instead (which had none of these challenges). Earlier this year I circled back and spent some time looking into the problem. The first attempt was to articulate the chassis as 4+2, pivoting the body to reduce the overhang -- a technique I previously used on the tender for my model of the Gr670. However, the Umbauwagen 3yg not only has a long 3-axle wheelbase, but also has a long distance between the outer axles and the buffers: Articulating the chassis as 4+2 would allow the car to negotiate turns, however it would also derail any vehicle attached to it as the buffers swung out widely. Further iteration yielded the general outline of my eventual solution: The center and end axles are connected together with a 6-bar linkage, rather than a rigid frame, allowing the chassis to change shape when traveling through curves. It's important to note that the center axle is actually what actuates the system. As the car enters a curve, the center axle is pushed sideways to follow the curve, which in turn angles the outer axles to follow the curve as well. The track cannot apply rotational forces through a single pair of wheels on one axle, and so a similar design to this one without the center axle would not work. You can see the mechanism here: The outer axles are mounted on 2x2 round bricks riding in a 2-stud-wide channel, allowing them to turn and slide slightly towards the center of the car in turns. I experimented a bit to find the best places for the pivots and a construction that would be light and reliable. In the final model I removed the blue tiles shown in the screenshot, to avoid additional friction and binding in the mechanism. Thanks for following along! As usual, I've uploaded some additional images to a Brickshelf gallery, including some notes on and prototypes of the linkage mechanism. Thanks for reading, and let me know if you have any questions!
Greetings, Train Tech! I build a lot of locomotives, but I hadn't really built any models of rolling stock with the same effort as I put into my locomotives. Until now. This is a model of a German Umbauwagen, or "rebuilt coach". They were constructed in the post-WW2 period by modernizing prewar compartment coaches, as the Deutsche Bundesbahn was strapped for cash at the time. They came in two main "flavors": the three-axle 3yg, and the four-axle 4yg I've modeled here. I initially learned about Umbauwagen while doing research for this passenger car (which itself was found while doing research for the glaskasten...). Inspecting an engineering diagram convinced me that it would be possible to build the 4-axle variant at my usual scale of 15 inches / stud (~1/48) and have it go around standard Lego curves. The main compromise I made was to reduce the length of the body from 51 to 50 studs. An even length made it possible to use the 2x8 double curved slope for the roof and the 1x4x3 train window. Since the window only comes in a limited palette of colors I wound up building in blue. My understanding is that Umbauwagen ran most of their lives in green livery, but I found photos of models in a variety of colors. I'd appreciate it if someone more familiar with these cars could shed some light on this subject. Of course, it's not much of a train with only one car... ... so I built two. I'm pleased with how closely the cars couple to each other while still being able to make it around turns. While doing background research for this model I came across Duq's rendition. Duq's model features an excellent rendition of the Minden-Deutz MD 36 bogie. Rather than just steal those, I decided to model the my cars with the Schwanenhals ("swan neck") bogies. These bogies have a somewhat American appearance with their arched outside frame. The buffers and stairs are attached to the trucks and rotate with them in curves. The trucks use Big Ben Bricks wheels. This may mark the first time I've completed cars without a locomotive to go with them. Full Brickshelf gallery here (pending moderation). Thanks for reading!