hertsbob wrote:mrennie wrote:the set of driving wheels and everything else except for the pilot and trailing trucks.
Righty ho. (Clearly I am a drunken Englishman, sorry about that)
So, I can cope with the concept of most of the model being built upon the driving wheels, but how do the other trucks (I presume we're talking about the same thing, except I've never encountered a truck up my nose - thankfully) know what's happening, and where they are relative to the rest of the loco?
That's partly taken care of in the engine blueprint, which is where you tell it the position along the track of the truck centre (actually the centre of the truck's top-level group in the 3D model) relative to the entire engine. I always put the driver group at offset 0, so the pilot truck (bogie) is at a positive x offset and the trailing truck at a negative x offset. The engine blueprint uses that information to work out the physics, like the positions where things should pivot. If you get it wrong, strange things happen, like the engine wobbling about, or rearing up on its hind legs, or toppling over, or flying up in the air. Where you see the various things in the visual model is entirely down to where they are in the actual 3DC model, since you export the entire model as a single intermediate geometry file. What is absolutely vital for that to work properly is to use the correct group hierarchy and naming. For example, with the 4-8-4, the topmost group is called locomotive and it has three child groups, bo01, bo02 and bo03. Then the wheels are children of those groups - for example, in bo02, we have bo02wh01, bo02wh02, bo02wh03 and bo02wh04. These group names are cited in the bogey blueprints, where you give the offsets along the track of each axle, but again, that's just to build the Physx model - it doesn't affect where you actually see the axles in the visual model. all the parts that should be fixed to the frame (boiler, cab, etc) are in bo02.
So, it all works as long as (a) the group hierarchy is right (it's all explained in the dev docs), (b) the model is built pointing in the correct direction in 3DC (nose pointing towards the top of the screen when you look at it in plan view) and (c) you export the entire model (every group and part belonging to "locomotive") to the same, single .igs file.
The tender works the same way, except that the topmost group is called "tender".
it allows me to get something rolling along the track as soon as possible
(pity I'm too late for the 1st of April).
