LEGO 4-wide narrow train prototype underway

I closed my "Shortened Maersk locomotive" post with a reference to my "next challenge." Well, here it is!  In a recent Bricklink haul video I showed some 4-wide track I had picked up, and late this week I started working on a strategy to put that track to work.  Part of me really wants to use some classic LEGO monorail in my city for an above-ground, short-distance transport system, but another part is strongly philosophically opposed to the idea of relying so heavily on such an old, and also very restrictive family of parts.  So, stubbornly, I'm trying to make my own substitution with in the form of a Power Functions-powered 4-lug-wide train system.  I expected this to take days worth of experimentation, so imagine my surprise when I had this functioning locomotive after only a few hours.

I tested it, and it has sufficient speed for my tastes, and seems like it works decently well.  However, I don't think I'm going to stick with this design.  I think my biggest issue with it is that the width with side plates actually comes to 5 lugs, rather than 4.  I want to try to do just 4, at least once, even if I then revert to something wider.

I've already come up with another engine with bevel gear drive to both axles and a vertically-oriented motor arrangement.  I'm now experimenting with different passenger car lengths and figuring out where to put the IR receiver in a sample train to make it fully RC.  I could probably live with it being *not* RC controlled, but if I can go the whole way, why not?  I already have the battery box issue figured out.  I'll share pics of the new setup once I make more progress with it!

Follow the trains topic to see the progression of this design over time!