The original plan was to see if I could get drivewheels to be properly quartered by playing around with the mesh and the hex a bit. The answer to that is a definite "yes", but unfortunately it has a glitch. This effectively makes it a "no" for any locomotives that have outside cylinders.
The glitch is that offsetting the crankpin 90 degrees (either clockwise or anticlockwise) to the usual location breaks the piston animation. That's the only problem. Everything else works.
The result is that the piston stays fixed, and its attachment point (where the connecting rod attaches to the piston) also stays fixed. The connecting rod is still animated, and is fine at the crankpin end, but due to the piston attachment point not moving any more the visible (graphics) little end of the connecting rod is no longer attached to the piston point. It's a bit hard to describe in words but easy to see in the game. The connecting rod graphics use the fixed piston point as a point to slide past, with the result that the visible little end oscillates up and down as it moves forward and backwards.
IOW, it's borked (for outside cylinders anyway).
Locomotives with inside cylinders would be no problem at all, because with those the little end of the connecting rods will never be visible anyway. So if anyone wants a properly quartered drivetrain on an inside-cylindered loco they can have it.
There's good news for outside cylinders though. Next trick I tried was setting the crankpin 180 out of phase, so it's above the axle instead of directly below. This works perfectly. So although we can't have quartered drivewheels we can have them "halved". You can't really see both sides at the same time on most locos anyway, but if anyone wants to the idea can be used to set front and rear drivetrains for Mallets or whatever 180 out of phase, just so they look staggered on that side when running.*
I've used the Beuth as a test locomotive for this idea since it comes with two separate connecting rods on each side (the usual one, plus a smaller one pointing backwards). This makes it easy to see what the changes are, since the smaller rear connecting rod stays in the default location and I just move the main one. The right hand side of the locomotive is standard. The left hand side has the main drivetrain 180 degrees out of phase.
The zipped files are attached to this post. Just chuck them in UserExtraContent if you want to see how it works.
Ok, so the next bit is "quartered" valve gear. Walschaert's gear has the crankpin for the eccentric rod trailing the main crankpin by 90 degrees. Like I said, I can get everything working except the piston animation working when things are 90 degrees off the usual location. That means I can get fake valve gear working, with the correct 90 degrees trailing, as long as I can do it without needing a moving "piston" component. This should be workable for a lot of locomotives, given suitable fudging of eccentric crankpin stroke, graphics, etc.
Unfortunately there is just no way of effectively animating the combination lever in RT3, but the rest is doable. The Beuth isn't really suitable for a convincing demonstration of this as it lacks the necessary bits, but I'll add it to the Schools class Beta sometime this week if I get time.
