A difference in speed doesn’t really make any sense. All wheels go (unless some sort of brake is applied) the same speed as the rest of them. The only factor that may slow wheels down is physical weight, but then all the wheels on said car would be affect and not just one. Also I had to look up what you meant by boggies/bogie because I didn’t understand what that was referring to. Then I saw that it was the UK term for the car trucks (as they are called trucks in the USA), and I understood a lot better. xD
I was talking to a friend of mine about how you would accomplish this (in Unity 3D mainly) and I thought that instead of having one single Spline to follow, you would have two. One for each rail (and then one that is the rail ties, but that is more of a visual thing then a functional thing). So instead of forcing the objects to following a single Spline (that right now causes the trains wheels to look like they aren’t even on the rail at curve sections), you have the wheels following two Splines. I know this is a game engine, but in real like a train can’t just run on one track (unless you are talking about a Monorail or MagLev train, which is a whole thing on it’s own) and are following two different rails. How would this change the whole formula/problem solving process? Would it make thing more difficult? Or easier?
Also if we used different Splines for each rail, there would have to be a system in place to make it so the user/developer could place both Splines at the same time (creating proper distance between the tracks and nice looking/functioning curve sections). I think even a editable spline/rail distance option would be nice, allowing for the use of Narrow Gauge track to be placed (instead of only standard gauge).
What do you all think about this idea?