Animating Tank Treads

[davvey]

Hi
An idea I need help with. I recently posted up a pack of script for vehicle rigging which was built using utility nodes and no expressions. I am now working on the same for tank treads etc. I have built a set of scripts to automate building wheels, treads, curves etc. and can get it to copy a tread as many times as needed to a motion path and set the offset to suit the tread size etc. I can also get it to rpaalce the "automatic" U_value with a connection to a rotating object which when rotated manually will turn the treads one full turn then stops. Do I need to set the paths to infinity both pre and post to allow the treads to move past one revolution.
I have an idea how to do it with an expression but am aiming to do it with utility nodes which will alow me to tie it into my other scripts which automatically generate wheel rotation when the vehicle is "grabbed" and moved back and for. This will operate the Tank wheels and would like to link the treads in as well but how can I tie this into the tread motion paths.

[drblacksnake]

QUOTE
Do I need to set the paths to infinity both pre and post to allow the treads to move past one revolution.

Does it matter if You can set each tread to jump
from end of path when it's uValue is larger than max U value of path
OR
from start to end when it's uValue is less than 0?

[davvey]

Hi

Not sure what you mean by Jump. What I want to do is get the treads to continue moving once the "maximum" or minimum U_value for the motion path is reached so that it continues round the path in an apparently continous loop. I gues this means jumpiong from a max to min or vice versa to simulate the effect.

[drblacksnake]

Yes, You've got the idea:

motionPath1.uValue = (frame % $sizeOfCycle)/$sizeOfCycle;

when sizeOfCycle = frame tread jumps back to start.

Are You doing all this stuff through combining utility nodes like plusMinusAverage and multiplyDivide? If so, then I'd say that's insane and worthless, sorry. A single expression node will work quicker, easier to understand, manage, change, than jungle of nodes (even if named properly). Especially if You want to do random forward-backward movements of treaded vehicle.

[davvey]

Hi

Thanks for the info I will try it and yes your probably right using nodes is insane for this but it is just an experiment in understanding uses for uitlity nodes and helping with developing my mel scripting ability further. I will let you know how I get on with it.

[drblacksnake]

Ok, then good luck. It would be nice to see what You've done (I am curious about number of nodes ).
On other hand nevermind my "insane"-thing because beginners will be happy about yet another way-to-do-things-quick-no-matter-how.. perhaps not only beginners.
"weird stuff, but if it works then close your eyes and keep driving".
Could You do "normal" mel/expr for same thing after? That could be a real boost for pros.
Actually if I'd gone to do such utility-jungle, then I'd first try to write an working expression and then replicate it by utilities.
Yet another plea-thing - could You add there some gravity thing for more or less loose tread-chain? As You probably have noticed they tend to sag between two gears/wheels under gravity. And they jiggle too while driving. That looks natural, man.

[davvey]

Hi

Thanks for the comments Utility nodes are not as easy as expressions but it does give direct connections and allows renaming and even duplicating with input connections and everything tends to work OK after duplicating.
I was thinking of using something like a jiggle deformer indiviual clusters located between each wheel and at the front and rear sloping sections. These would be individually adjustable or as a group. Also by using nodes for wheels etc it allows the stopping and starting of individual wheels to simulate damage etc very easily.
Do you have a simple expression for animating something like this especially if it tied to the movemnt of something like the tank body. If so I could use it as the basis for my nodes etc. Image below show parrts generated by the scripts based off a few simple user input sizes the scripts will make wheels tread etc and a low resolution body which can be replaced by a more detaile user made body very easiy. Also the scripts produce low resolution objects for wheels and treads to allow "real time " animation if required.

[drblacksnake]

Expressions work also after duplication and/or renaming of nodes and (instead of nummerous utility nodes) they form some logical code, so thats not an argument.
Well I have no rigged tank-tread-things besides there's nothing complicated, so You can figure expression for such kind of things easily - it takes more time to set-up than to write expression for this kind of stuff.
At least as far as I remember it was one string of expression per each tread, while converted in nodes it will take at least 3 nodes per tread. I imagine what will work more efficient - a single expression for 40-tread chain or funky network of more than 120 nodes. Pardon my scepticism, which is based on experience of opening 2-3yrs old [often anonymous] projects - it takes considerable amount of time to understand what was done at those times (or even guess who was that idiot who made this all so complicated, even if it was me).
If I were You, I'd thought about doing stuff both useful and easy. Well, I am not.
P.S. afaik Your image looks technically wrong - there's 1-2 pairs of geared wheels on front/rear axles whose drive treadchain, other wheels are just supporting chain (upper ones) or whole vehicle (lower ones). What was intent of this set-up?

[davvey]

Hi

The image shows a Lead Wheel a row od smaller iodler wheels at the top aand some of the larger wheels on the bottom row which support the vehicle etc.

In terms of utility nodes you aree probaly correct about an expression being simpler but it is just a learning excercise at the moment so using nodes is making me look at scripting in a different way and "forcing" me to learn more about the workings of things like motion paths etc.

This image shows what my initial design was trying to do but the UI for the script will allow the user to select number, size and placement of wheels to be set before construction or after building wheels they can be adjusted before building the tread curve patch which detects each wheel position and builds a path to suit.

[davvey]

Hi
Just an update and answer to my own question
Believe or not they say the simplest solution is the best and by accident I found it in this case. I opened the motion Path in the connection editor and connected the X axis rotation of an object to the input motionpath and it worked for all angles of rotation both positive and negative.

The line used was as follows

connectAttr -f pCube1.rx Lf_Tread_MotPath1_uValue.input;

I had been using

connectAttr -f pCube1.rx Lf_Tread_MotPath1_uValue;

which allowed a connection but didn't give an output passed a uValue of 1.0 i.e. it stopped once the maximum value was reached now it works great.

[drblacksnake]

as far as I got, You have to rotate cube, to get it run along motionPath again and again? if so, then how do You get constant speed of it during one cycle?
at least idea sounds like a goodie!

[davvey]

Hi

The script pack I built for vehicles will derive wheel rotaion from a keyframed animation cycle or via utility nodes which calculate the actual rotaion based on the square root of (x^2 + z^2) of the vehicles body. Also vehicle body rotation and direction are factored in as well.

These two outputs are fed via a adddouble linear node to each wheel rotate group node and this could also be fed to the UValue.input above.

I will let you know how I get on with it.