Don't worry about that, I'll manage through .dll magic I know very little about trains, but i'd say the axles are articulated so that they can take turns.
It would be pretty hard to simulate a full rollout from the vehicle integration building, because in Baikonur the distances are huge. Also the train makes stops in different areas for fueling, the ILS manual says there's a specific fueling area for the Briz upper stage. Propellant used for Proton and Briz is very toxic but also stable at ambient temperatures.
Right now my best bet would be to manage all those meshes (rocket stages, fairing, train...) as a big animation of the launchpad. It is a bit tedious from a coding standpoint (because we need reference points and vectors for everything), but there are few limits to what can be done, and there would be no problem with time warp. In theory, provided we can get the vectors and points, a 50km rollout animation is possible. In theory. Then, when the animation is complete (rocket standing on pad), we spawn the whole rocket stack and dock it in the correct order (the launchpad controls all of this). There will probably be a noticeable "lag" at this point, but that's the price to pay. Simulating the train as a physical vehicle rolling on the ground would lead to many problems, including time warp.
I'll start small making the train arrive and erect the rocket, once that done we can explore how far we can push the thing
Modeling the launchpad interior took me to understand a little bit how it works... Quite a complex and well-designed megastructure !
The "cross" matches the one at the rocket aft, its a big contact plug. The hexagonal ducts channel the exhaust to the pits, from where it exits into the two flame trenches. The green cylindrical shape is actually a closed blast door, that should be open in two parts. It very probably closes with a huge spring-like mechanism held by the rocket mass, swiftly protecting the vulnerable parts from incineration. The "aerodynamic/conical shape" is then well-suited to deflect most of the exhaust coming at it. I read somewhere (Anatoly Zak) that the central contact "cross-plate" falls into the central cylinder, and that there are doors to protect it (still have to figure where are those, maybe it just flips like a coin).
Still a lot of work, but I'm beginning to see the big picture. I must say I had no idea how it worked when I started modeling. But that's the cool thing you have to understand it a bit to model it decently Also the "metal plates" I modeled on the rocket body, right below the "black stripe", at first was simply a "cool detail", but now I figured out those are hardpoints on which rests a great part of the LV mass (the mass - up to 690 tons ! - is distributed along those 6 "arms" and the bottom contact plate basement).
It wasn't easy, but I managed to have the doors opening/closing without hitting the rocket radial tanks :
Launchpad with all doors closed and arms retracted :
Also started to work on the "erector" (sorry, that's the technical word)... Actually it lifts the whole wagon on which the rocket is carried, amazing. They simply detach the locomotive and the power/air conditioning wagon.
Still work to do on the pad mechanism, there are quite a lot of moving parts, and getting everything to scaled and lined up is no small task.
But now we have an accurate railway, rails are modeled after the Arcelormittal "R65" russian rail type, with of course the 1520 mm "russian gauge". Railway crossings are the standard 2700 mm russian type (concrete). I won't forget to let some spacing between the rails, because in Baikonur you can have -40°C in winter and +40°C in summer, so rail lenght can vary greatly, you have to be careful else horrible things happen like "accordion rails".
So the "lid" of the block that faces the railway opens (saw that on pictures), letting room for the erector and clearance for lowering the rocket into the silo (the design doesn't seem too far from an ICBM silo, except that the rocket was probably too big to be fully stored underground, which was a no-go for a military use).
Also @MaxBuzz found that drawing I used a lot for modeling the mechanism, it shows how the wagon remains attached and is raised with the rocket.
Патент RU2353560C1: Изобретение относится к космической промышленности и может найти применение в области строительства. Тележка ходовой части мобильной башни обслуживания содержит несущий опору башни корпус, опирающийся на колесные пары. Корпус выполнен со сферической опорной поверхностью для...
Its a good idea to check early if the rocket fits the gantry tower... Seems good, of course the UR500 looks very short, but it has a shortened second stage and a simple nosecone. The tower we have here is the "final" one, in reality they added floors as the rockets grew taller. We might do that one day, would be cool to show the evolution of the tower in time. Still a lot of work, that tower is a very complex object.
The "backside" is really scary, there is a crazy amount of beams and struts, stairs, wires, walkways everywhere...