Walmarts valve gear (cheaper than Walschaerts).

[Gumboots]

Animated gif below. Click it. You know you want to.

Ok, this can be done for any RT3 loco model that runs external valve gear. This method is really easy to set up. The amount of polys and code required isn't much, so we don't need to put up with the usual frozen valve gear graphics on any new or revamped locos. This is not a full simulation of Walschaerts gear, but is more fun than the default stuff and is good enough to amuse the average gamer. Well, good enough to amuse me anyway.

I think this is about the best that can be done without huge amounts of time and effort. Making it more realistic would not be easy to set up. I have thought about it, and the limits of RT3's coding mean that anything more complex than this would rapidly get really hairy.

Edit: Oh yeah and if anyone is curious, doing Stephenson valve gear to a reasonably faked standard is pretty easy too.

[Gumboots]

Oh forgot to mention, it can easily be done with the valve gear 180 degrees out of phase to the conrod/coupling bar. That gif has it all in phase, so the valve stem goes forward when the piston does (which is sorta close to how real valve gear is), but I can make the valve stem go backwards when the piston is going forwards. Can only work with 0 degree or 180 degrees difference. Other angles break RT3's animations.

I'll animate the 180 degree version too just to see how it looks. Since this is just eye candy for fun, if the other way looks like more fun then anyone can use that instead.

[AT41B]

, What would also look neat is some way to designate the leading truck wheels turning.

[Gumboots]

Oh that's easy. That gif was made by taking 10 shots in Blender, with 36 degrees of drivewheel rotation in each shot. The geometry is the same as what will run in RT3. I just wanted to see how it would look before I started pigging around with .3dp files and all the rest of it.

I didn't bother rotating the non-driving bogies on the trucks. Even if I had it wouldn't show up, because those are currently using a standard procedural material in Blender. That means they'd look the same even if they were spinning, because the material is even over the whole surface. Once the thing is running RT3 skins the wheels will look like they usually do, so if they spin (which they obviously will) then you'll be able to see it.

[Gumboots]

So I couldn't stop thinking about this stuff, and I think I've figured out a way to get the whole lot working with the valve gear trailing the main crankpin by 90 degrees. It all seems to be working ok as far as geometry in Blender. It's not absolutely perfect, but so close that it probably won't be noticeable in the game. The game engine is the tricky bit, because that can do unpredictable things at times. If it decides to behave consistently then I reckon I can get this to work.

It relies on extra drivewheels with hidden connecting rods. There's the normal drivewheel, which drives the conrod, coupling bar, and the valve gear eccentric crank and eccentric rod.

Then the coupled wheels behind the drivewheels (which have to be there anyway unless the loco is *-2-*) are coded as drivewheels instead of bogies. They then have their own connecting rod, the only visible portion of which is the valve gear expansion link. This makes it operate at a different angle to the eccentric rod (due to different conrod lengths on the same stroke) while still matching up the connection between the two over one full revolution.

Then there's a third (invisible) drivewheel, which for the test Garratt model I've placed smack in the middle. IOW, it has a really really long (invisible) conrod that only moves over a very shallow range of angles. This lets it animate the radius bar and valve stem graphics (which are part of it) without them swinging all over the place. They just move forwards and backwards almost linearly, or near enough to it. Naturally this has the same stroke as the others for the valve gear, so matches up for connection points.

I'm out of time to play with it this morning but will work on it later tonight. I won't get it running as a test model in the game tonight, but should be able to finsih the basic test animation to see how good it looks. If that's ok, I'll look at coding up .3dp's to handle it all in the game. I have a fair idea of what the pitfalls are likely to be, and think I can work around them. Won't know for sure until I try though.

[Gumboots]

Ok, here it is. This one is trickier to set up, and could probably still be improved slightly, but it gets things moving with the valves 90 degrees to the main crankpin. Doing this requires that all the visible valve gear parts are actually parts of connecting rods. Pistons don't move when initially set at 90 degrees. It breaks the piston animation, but connecting rods still work, although they don't work quite the same way as normal.

[Hawk]

Heck Gumboots, that looks fine. Good work.