Although you are asking me questions via PM I think that you should put them in this thread because that way other people who are interested in train gears can use the information and links for research.
That is why I am posting the answer here not via PM.
For a bit of context:
Your question first question via PM was “Does your wheel gear only work while stationary or can it follow a track left and right and up and down?”
For anyone reading that has not seen my gear it is here in this thread:
The answer is “Yes it can follow a curve up and down and around corners”. I have explained to you how I do it and even made a file for you (in 2.73!) to demonstrate it. (in my last post)
Your next question was:
“when will you put in the piston arm connected to the wheel?”
In your file you only modeled the 3 wheels and the connecting rod. Sorry, I am not going to model and rig a whole gear system for you, but I can give you some links to useful information.
If you look at the videos I posted in the Flying Scotsman thread you will see that I did model and synchronize (more or less) the whole 3 cylinder gear system. The flying Scotsman’s gear was designed by Nigel Gresley. There are many variations of gear systems used for different trains.
Most steam trains use variations of the “Walschaerts Valve Gear” Nigel Gresley’s gear is one of them.
I can not explain to you how an entire gear system works, it is too complex to explain via messages like this.
I can not do that research for you, you have to do it yourself. If you want to model a train with a working gear and pistons you have to understand how these gears work.
There are many different parts to these gears and for them to work as a mechanism each part has to be an exact size and exactly placed. Changing one measurement will effect the whole system.
If you are really interested in these gears I can give you some good links.
The most valuable source I found for making a working gear was this gear simulator made by Charlie Dockstader (rest in peace and thank you for sharing your knowledge)
In this page there are links to his work:
It not only gives you working simulations of different gears, it allows you to design your own versions changing the parameters, it will even tell you the efficiency of your gear design and if it will just blow up! A badly designed steam gear can explode.
The simulator will also tell you the measurements of each component.
I recommend you download the “all in one zip” and the pdf instructions.
Here is a tutorial by Locomotivist of how to rig a Walschaerts Valve Gear (I did not use this exact method but I did use the part that explains how to rig the combination lever):
Last but not least here is my version of a simple rig for Walschaerts Valve Gear. I was able to append the rig I made into blender 2.73 so it will work for you.
This is not the Flying Scotsman’s gear it is a generic Walschaerts gear in its most simple form. I based it on the Walschaer’s gear animation found in the Wikipedia.
(The file also uses a driver so in Blender 2.73 you have to enable “auto run python scripts” in user preferences for it to work. In modern versions of Blender this is not necessary)
Here it is:
WalschaertsGear2.73.blend (218.8 KB)
You are welcome to use use this rig (anyone is) but you will find that to be able to use it properly you have to understand what each component does and how the gear works in real life.
I think it is more useful as a reference of how you can rig a gear for yourself.
In 3d things work backwards from real life, instead of the piston driving the gear to rotate the wheels, in this rig it is the wheel rotation that drives the gear to move the piston.
The most complicated part of the rig is the very long vertical bone that swings influenced by 2 IK systems ( one from the main rod and the other from the radius rod) to work the pivot point of the combination lever (see the tutorial video by Locomotivist to understand it)
If you change any of the measurements you will find that it no longer works properly, you would have to change all the other parts to compensate. This is why the gear simulator becomes essential for a working model.
All this is an extremely complicated process you will not be able to do it without a lot of research on your part.
My advise to you if you want to model a complex working steam train model is:
1 first research how the gears work and what each part does in real life (google, Wikipedia, the links I have given you etc.)
2 Then model your train at the world origin (leave the gear till last) It is best to stick to a train that actually exists and you have references of.
3 Find out which gear version your train uses.
4 use the gear simulator to tell you the measurements and placement of all the moving parts. You have to find a gear system that matches your train there are many gear templates in the simulator.
5 tweak your model (wheel position etc) to the correct position and model all the moving parts placing them in the correct position according to the gear simulation.
6 Make the rig snapping all the bone ends to the exact pivot points of your gear components.
(to do this you will have to understand exactly how the rig works) Add the IK systems etc.
Remember it is the wheel rotation that drives the whole thing.
7 THE VERY LAST THING TO WORRY ABOUT only when your gear works properly with the train “static”, is to parent the rig to a bone that follows a curve.