Atomic Systems

I honestly don't know how you other guys do it, I can build great models (only fictitious trains) that look right, I can even get the proportions right now.

If there's one thing I still cant do its valve gear. I can build it, fine, but animating it, long tedious and badly done. It wobbles all over the place and moves horribly unrealistically.

How do you do it, if there's one thing that I keep seeing its bazzamotion, that's probably some silly name a basic way of animating it, but every tutorial I've come across doesn't seem to make any sense, and I've tried a lot of ways, and I can't seem to lose the wobbles.

Only other things I'm stuck on is lighting for renders, but that's not stopping MSTS stuff.

To do animations properly - you need a proper grasp of what everything should be doing, how to set it up initially and a knowledge of trigonometry (or Paul's calculator )

I think it gets easier as you work through the 3 steps of concept, set-up and animation. Try and find a model with a similar valve gear to the one you are working on, and see how the different bits move on the slowest animation speed possible in Shapeviewer. Then have a read of the valve gear tutorial at Steam4Me and see if it makes sense.

Regards,

Dan

Try a (tank) loco with simple motion, such as Stephenson link. I'm having a bad run with Walschaert at the moment.......so we all have our good and bad days.

Hard to give firm advice on getting it right.....because some 3d modeling software treats animation differently at the interface. The most difficult rod to do is the connecting rod between the mainlink and crosshead. The end opposite the pivot tends to wiggle, no matter how much care you take with the animation.

Cheers Bazza

myles,

I found somewhere an animated Walschaerts motion, if you can't find it email me & I'll send you a copy. There is also, on the net, a program with about 20 types of motion.

http://www.alaska.net/~rmorris/als2.html

Walschaert's motion is easier than Stephenson - it's like taming a barrel full of jelly. All motions are like the song about bones - one thing drives the next thing which pulls the next....

I find false pivots & rods are the most useful trick - fortunately you don't have to know trigonometry, just follow one pivot with another.

I found Gmax to be better than TSM for animation - I can't use 3dstudio. With all systems make sure the parts aren't moving in the X axis.

Read the animation & TSM loco tutorials on steam4me - the principles are there. Animation's a bit tricky at first but once the penny drops it's plain sailing.

Richard

I understand where things should go, its just getting everything to follow the right paths. There must be some sort of animation constraint or something?

Getting this to stay on the same path seems almost impossible, I do however tend to get lengths by eye, I will build a driving wheel set to the measurements in one of those programs, and see what I get, I can only hope for the best. A very good find those!

Myles,

Which program do you use?

I can only help you with TSM or Gmax.

Take a connecting rod - You have the length from the drawing you're using, always use the best drawing available - set the pivot co-incident with the pivot point on the wheel - the crankpin. Link the rod to the wheel - the rod will turn like a windmill sail when the wheel turns .

Make a small cylinder as the position of the small end at the piston end of the rod, make it 8 or 12 sides, leave it in the centre of the loco - makes it easier to delete it after. Join the pin to the rod - it doesn't have to be physically joined. Make a box in the same plane as the crosshead - in most cases this will be horizontal - the same size as your pin & long enough to exceed the crosshead travel.

At all points of the rotation the pin & false crosshead should co-incide.

Rotate the wheel one step, isolate the rod & set the program to 'rotate' The rod will have windmilled with the wheel, with the mouse rotate the rod until the pin covers the false crosshead, lock it.

Repeat the process for all steps of the rotation.

The mouse isn't sufficiently accurate; in TSM go to the 'transform' menu - then 'rotate'; in Gmax use the window at the base of the screen.

With all programs it's easier if you just have the wheel, parts to be animated & guides showing.

It's easier to do than to describe; I suggest you get to know your program better. There are useful tools hidden away & largely undocumented. Some of the flightsim & car modelling tutorials are very helpful. Dig through the Gmax & TSM forums on this site.

Richard

I think Walschaerts valve gear must be one of the most fiendishly complex!



Regards,

Dan

Thanx for the tips, I dunno if I could stand walcharts yet though.

I can do the connecting rod between the wheels, its the crosshead and associates that always get me. I'll have a go with me interpretation of what you said cua193. Though there is no guarantee I'll of understood it. I use a mix of 3DS-Max 7 and Gmax by the way.

EDIT: Initial attempts have proved that I either a. am missing something vital or b. I'm right and the wobbles are between the animation frames! (using 16 frames -would more cure it?)

I don't understand what you mean by wobbles; either the steps are irregular - in which case check your maths. each step must be 22.5 or 45 degrees.

If the movements are lateral you must be introducing an animation in the wrong plane or you've accidentally pulled the parts across the frame. make sure the 3 axes are shown in the windows at the base of the screen & look for values which shouldn't be there.

Don't bother with more than 16 frames - it can be done; Decapod explained in an earlier thread, but isn't worth it unless you're building something like a Stirling Single.

The Britannia pic is useful - you can see the eccentric link fixed to the wheel & the expansion link with a fixed pivot joined by the eccentric rod with a known length. Use false circles as I descibe in the tutorial to establish the movements. Fix the top of the combination lever at mid travel & work out the drive from the crosshead. Reverse the pivot to establish the valve movement - this is the tricky bit. The last bit could even be omitted at mid-travel - you'll hardly see it.

Richard

It's hard to explain, the part that should be in the crosshead, bounces up and down along its path, like it were being dragged across bumpy ground. But they happen in-between frames, it doesn't move from frame 1 to 2 for example, it seems to have a 1.5 that's about an inch higher than it should be.

It's occurred to me it might be a 3DS-Max thing, it shouldn't be, but in any case, I'll try building an accurate one in Gmax and see how that turns out.

Could you tell me where this tutorial you mention is, it may be the one I've tried, in which case , it all seemed like a good idea, but I still couldn't get it to work.

I think its me, I'm doomed to inside cylinders forever.


EDIT:
Weather I did something Majorly different without thinking , or it was just a Gmax/3DS-Max thing I dunno, but I appear to have lost the wobbles on my test set. I'll trial run again exactly what I did in Gmax in 3DS-Max now.

myles,

The tutorials I wrote are on the steam4me site:-

http://steam4me.railpage.org.au/trainsim/tutorials/

There used to be another on train-sim.com.

Perhaps I'll do a quick tutorial about Walschaert's gear - any suggestions?

Richard

Humm, I seem to remember trying that before, but I'm gonna try it again.

As I remember I did it in 3DS-Max, but I did exactly the same simple animation in 3Ds-Max and Gmax, and in Gmax it was perfect, yet in the other, it wobbled. I will go through the whole tutorial again, in Gmax,

Thanx for that. I'll keep trying, one day I'll get it, hopefully soon. As for a walchaerts tutorial, yeah Great!, by all mean sif you have the time and inclination, I'm sure millions would use it

A tutorial for Walschaert valve gear certainly would be welcome Richard

By the way, to help with identifying the bits on the that type of valve gear (as fitted to BR Standards) here is an illustration from the Black Book:



Regards,

Dan