witchy

I would do LBG+DBG; even if the DBG is lighter than the IRL colour, the contrast with other locomotives with black parts would make this one more distinctive. The second picture especially looks quite close to the LBG+DBG combination so it wouldn't even be much of a stretch. The one place where I think black parts have a place would be in the inner structure of the frame, behind the DBG details, to represent them being shadowed and slightly highlight the contrast with the LBG top. Combine that with a tasteful application of pearl dark grey and suitable silver on the cylinders, running gear etc. and I think it's going to look pretty striking.

I've upgraded Stephenson's Rocket with a number of improvements, including chimney stays (a regular Lego string) and improvements around the cylinders, especially the feedwater pump on the right cylinder which is now using a golden crowbar. Also, a brickbuilt stretch of accurate L&MR track as a display stand. More photos at: https://www.flickr.com/photos/198768132@N07/albums/72177720311012954 Studio file and instruction PDF at: https://drive.proton.me/urls/JA2SWZJ9YR#cDelYZR44v0W

Alright, so the most established definition of midi scale as a well-defined thing would be 5 plate tall figs, meaning it would be better to have yet another name for the 1:64 scale with 8 plate tall figs. It's getting hard with all these scale names , what even would be between minifigs and "midi"?

Oh, interesting. Midi scale is not a term I've heard before; it appears to be generally somewhat ill-defined with "midi scale" spaceships ranging wildly in their actual scale, with the only uniform factor being that they're a "convenient size" smaller than minifig scale but larger than microscale. I guess in that sense my relatively precisely defined 1:64/1:62.5 counts as a "midi scale", being a convenient size smaller than minifig scale L-gauge but larger than the HOish 4wide, or 2wide micro trains. Your well-defined 3wide (which seems to translate to a scale around 1:100-120) midi scale work is neat; I especially like the "studs towards end" solution to the SNOT details on the Chicago Metra passenger coaches.

The model is highly recognisable and the thoroughness of the detailing is impressive, especially with how I don't see any obviously illegal or particularly dubious connections. I particularly like the use of bucket handles as shades over the windows, and the side rods are quite nicely built too. However, some of the shapes are pretty blocky, especially near the lower front. For the cylinders I'd consider using 3386 brick round 1x1x2/3 with side stud with a 1x1 cheese slope on top to represent the characteristic shape of the I K, although this would make the cylinders all black. The size of the central buffer also seems similar to the cylinders in the prototype, so the 1x2 rectangle looks a bit big and square. A piece like 79194 plate 1x1 with bar handle (held in a clip by the handle) or 20482 tile round 1x1 with bar (bar inserted into a jumper hole) might give you a closer representation of the prototype in this regard.

L&MR trains obviously need some proper L&MR track to run on. Using jumpers for sleepers loosely inspired by Hod Carrier's brickbuilt narrow gauge track, but with a completely different general structure. The track on the left is easy to make and trains can run on any adjacent pair of tracks (legend says the L&MR track was designed to allow that for oversized loads at off-peak hours, but not all sources agree on what exactly the gauge of the central pair was). The track on the right lines up correctly with stud spacing and is compatible with standard narrow gauge tracks, but the central pair is too narrow for train wheels to fit properly. Edit: This version lines up with studs even on the outer plates, but the ballast bed ends up wider.

Regarding the drivetrains, here is my standard solution from Planet, a variant of which is also used by John Bull and the Lafayette-ish Norris. The brown goo is tungsten putty from a fishing supplies store, which appears to be by far the best material for ballasting (Planet has about 35 grams of plastic and motor, and I've ballasted it up to 70 grams total weight so far, and it still needs more to be motor-limited rather than adhesion-limited). It sticks to itself more than it sticks to ABS, so you can fill all reasonably accessible cavities in a reversible way as any residue can be swabbed off with a small ball of putty held by fine tweezers. The axle also doesn't need to be metal, I just tried it as another source of ballast (the small bevel gear is also metal, adding another 0.4ish grams to the loco). The mine cart wheels seem like a significant bottleneck due to their apparently extremely high resistance, so I'm waiting for an order of custom #2 wheels to see if it can be fixed by using Technic axles instead. If even technic axles fail to yield a significant improvement, custom ball bearing wheelsets using 18677 to hold the bearings could be the ultimate solution.

Just waiting for a few Bricklink orders to finish so I can photograph the physical builds in proper configuration. I'm also planning on making instructions for each model available to the public as soon as I'm done tinkering with each and have checked that they work physically. Also, a Norris 4-2-0 (aesthetically based off B&O Lafayette but not to precise scale: e.g. the drivers are too large when counting the flange, which I usually do in this scale, beause the front truck won't work properly if I use smaller wheels; the boiler is also a bit too short based on a quick search, but I didn't want to add another stud to the length due to proportions and structural considerations). This is also motorisable and the tender has been designed with electronics space in mind. I'm expecting it to have the best running characteristics of the locomotives I've made so far, as Planet and John Bull suffer from short wheelbases which reduces the weight available for adhesion and makes ballasting more challenging. I'm slightly concerned about the sturdiness of the driver mounting in this one though (nowhere near as sturdy as Planet, which is rock solid) as my earlier experiments with 0-4-0s showed that the motor loves to tear driver mounts apart. In the worst case I can add an ugly but functional set of external frames like in John Bull, but that would severely detract from the aesthetic.

I managed to figure out something reasonably satisfactory for the Camden & Amboy Railroad John Bull and its tender. The front truck is functional and the tender should have a reasonable amount of space for battery and radio equipment.

1:64 (or, to be precise, I usually scale to 1:62.5 where 1 plate is 20cm/8" and 1 stud is 50cm/20") is a very convenient scale for making people because you have 2 bricks' height for the legs and body, and 2 plates (or more with tall headgear) for the head. The width of such people is roughly 0.5m which is reasonably close to a train seat, so depending on how thick you make the walls of a 6wide coach you can easily get a realistic number of passengers side by side (on the other hand, trying to get 4 minifigs side by side would require the train to be at least 13 studs wide). This isn't a train, but it's another example of what you can do with the scale; a 1830ish Royal Mail stagecoach, with the guard having a bugle and a shotgun. I haven't figured out how exactly to do the horse harness yet (I need to study how actual coach harnesses worked in the period, and the build would probably end up relying on flex hose a lot). The Houses of the World sets are, incidentally, at a scale that matches these trains and people well enough to be compatible on a layout.

These are not true 4wide, using narrow gauge track to represent standard gauge in 1:64 scale (modern rolling stock would be 5-6 wide), but they are 4 studs wide due to being old and small: The Rainhill trials contestants, from left to right: Cycloped, Novelty, Sans Pareil, and Rocket. The gears on Novelty and Sans Pareil are acting as stand-ins for third-party #4 wheels. Stephenson's Rocket and its evolution as an engineering testbed; from its Rainhill trials condition, to getting a more utilitarian paintjob and lowered cylinders, and finally having the steam pipes moved inside the boiler Liverpool & Manchester Railway Northumbrian with a 2nd class consist L&MR Planet with a 1st class consist. This one can actually be motorised with a Studly Trains micromotor and is capable of pulling 2-3 coaches with some tuning (ballasting all open cavities, using higher friction o-rings for traction, lubricating the coaches). The tender is designed to fit a Deltang or similar receiver, and a small battery. And on the American side we have DeWitt Clinton of the Mohawk & Hudson Railroad with Goold cars. The cars have passengers both inside and outside (the inside passengers are actually load-bearing) but it isn't very visible in the renders. I also have a motorised John Bull in the works, with its weird 4-2-0 layout that looks like a 2-4-0 being authentically represented (only the rear axle is powered) but the tender needs a bit more work first. I've built Planet, Rocket and the L&MR coaches, and the rest should also be physically buildable without severely illegal connections (although some are fiddly to assemble) or third-party parts (except for the motor and associated electronics in Planet, which are optional, and the #4 wheels of Novelty and Sans Pareil). I've also generally avoided excessively rare or expensive parts, and where they have been used (such as the medium blue 4081b in the light blue car) an acceptable substitute of a different colour can usually be found.

To be precise, as the length of this track is measured near the inner rail, to have a R50 circle at the centre of the track you need a radius of 47 studs at the hinge position, giving a hinge circumference of 295.16 studs or ~148 segments (round up to 150 segments for convenient round numbers). The pictured curve has a 2 degree angle between each segment, which would give a hinge circumference of 180 segments, so the desired curve is only slightly tighter than pictured (2.4 degrees per segment) and appears viable to build in the manner pictured.

Like this. Cost (in efficient colours) is around £2/2studs, or around £300 for a circle of R50 (80 cm diameter). I've tested the narrow gauge equivalent and it works, at least in large enough radii. In tighter radii it may be necessary to build each rail independently so that the outer rail has more segments, to make the gaps smaller. This is left as an exercise to the reader. The plates with the rail need to have 4 studs and 2 plates between them, otherwise they will interfere with wheel flanges as the regular rails are slightly narrower than the thickess of a plate. The flex hose sections should be lapped so that the joint of one is in the middle of another. The print on the studs of the wedge doesn't seem to foul the snot pieces above because the hole in technic pieces is slightly higher than would be in system, so the rest of the light grey plates could also be replaced by a 2x6.

Would narrow gauge track work? R48 would be quite close to the size you're looking for. Otherwise the most reasonable option is to accept a slightly different size from standard R40 or R56 track. If you like spending a lot of money it is also possible to brick-build rails to the exact specification using 32028 but that is a lot of effort and expense.

Using third-party R56 track would get you a diameter of roughly 90cm. At least Trixbrix and HA Bricks have R56 track available in Europe. Other than that, another option is using straight sections between some of the curves. Alternatively, mixing R40 and R56 curves (specifically, every other piece R40 and every other R56) would net you a diameter very close to what you're looking for. In the latter two options the frequent curvature changes may make the tracks and the trains running on them look a bit weird.