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Hi, all! After piddling around with some small projects for the past few months, I decided it was time for a challenge! I'm building a Power Functions steam locomotive where the locomotive is powered (as opposed to a tender). To make things harder, the prototype isn't some small shunter, but the 2-10-2 China Railways QJ: The QJ is a fairly large mainline engine whose roots can be traced back to the various German 2-10-0s used extensively during WWII. Its primary claim to fame is probably the longevity of the design and quantity of units built - 4700 between 1956 and 1988. The QJ was used extensively on Chinese mainlines throughout the latter half of the 20th century, and a few soldered on in revenue service toward the end of the 2000s. Three survive in the US, two owned by Iowa Interstate, and one by RJ Corman. Anyway, I've decided to do a log of the build and share some of the process. We'll see how this goes. As always, the first step for me is finding drawings. I had previously wanted to try my hand at some smaller Chinese locos like the SY or JS, but having not found any drawings, the QJ was it. Resized to my usual scale of 15" per stud, it looks like this: The next task is to decide on the layout of the chassis. The "obvious" way to do it would be Emerald Night style - 2-10-2 with a blind-flange-blind-flange-blind configuration for the 10-coupled section, but this method results in a lot of overhang on curves, especially so if the body is attached directly to the 10-coupled section, and I really don't like that. That and other issues with the 10-coupled arrangement led me to look at more fun (complicated) designs, and I eventually settled on the following: This is a 2-2-4-4-2 articulation where the cylinders are actually locked to the middle 4 wheels because that's where the drive rods will connect. This arrangement lets me have driving and connecting rods across all flanged drivers, which I really like, and this also keeps the maximum width of the chassis at 9 studs at the cylinders. Yes, the 3rd and 4th axles aren't visually connected, but I would prefer having a gap over a thick or uneven connecting rod (full/overlapped half beams). At this point I had a vague idea of how I'd connect everything together, so I dumped it into LDD to sketch out the overall shape. Here I've just thrown together my intial thoughts of how I'd build various parts of the loco just to line things up with the drawing and evaluate the overall look and feel. I start like this because to me it's much more important that the overall proportions of a locomotive are correct and less important that individual details are all modeled. Now we can start on the detailed design. The first issue I tackled was the all-important method by which I'd connect all the axles that weren't already linked with connecting rods. To that end, I had known I would probably use a mechanism I had already used multiple times in the past, but I spent a lot of time trying to make it more rigid and compact. I also discovered how much easier it is to compact various assemblies by going to an all-studless chassis. Next up, connecting motors to the now coupled drivers. This has proven to be by far the most difficult part so far. One of the things that's really important to me is minimizing the overhang of the locomotive body inside and outside when it goes around a curve. To adjust this, you can move where the body pivots on the chassis (typically two points, one toward the front and one toward the rear - on a diesel these are the points at which the body connects to the bogies) forward and backward. The catch is, now the drivetrain connecting the motors to the wheels has to flex through these points as well. I settled on an initial design like this: As you can see, the drive train comes up from the last driven axle through the point at which the trailing axle is connected. Then it goes backward and there's a univeral joint through the point at which the body is connected to the last axle. How the motors are supposed to be joined to each other and to the wheels is still unclear here. At this point, I decided to make a mockup and do a test run, because you never know if things you make in LDD are going to work in reality or not. In this case, it did not. Turns out that the joint above the last driven axle was far too flimsy, and trying to transmit any significant amount of torque through it would throw the rear drivers off the track. And so here I am at the moment: This is actually the first design that made it around my test track, and it seems to do so fairly reliably for now. You can see the (yellow) more rigid redesign of the flimsy transmission and the (orange) more detailed design of the first driven axle. The actual testbed is not quite as pretty colored: More updates to come, stay tuned!