Nail Constraint Lenght

[ssnovahv]

Hi,

i would like to have a suggestion on how you can animate the lenght of a nail constraint.
example:
you have a motor(winch) moving on X axis. a weight is hanging on the cable and for that i'm using a nail constraint (motor - weight). if i create a nail constraint and set the initial position to let's say 5, then a contorsion1 node is created and the adsolute position (.ty) is set to 5. This is not standing for the "lenght of the cable". is there another attribute i missed?

any ideas?

thx a lot!

[joojaa]

You shouldn't use rigid body constraints for things that dynamically update. Im pretty sure you can do it tough but what happens is another question. Really not something you'd want to use rigid body dynamics for.

In general don't use dynamics if you can simply animate it by hand faster than you can do the sim. Only use simulation when theres too many variables in play for you to handle in sane amount of time. Even so you dont need ALL of it to be dynamic just the part that causes the uncontrollable effect.

[ssnovahv]

Hi Joojaa,

nice to see your name.

i agree your answer if it's for animating purpose where precision is not that prior, but if i want to simulate the swing of the object who is lift up by the winch and need to "exactly" know how far and how long the object is swinging, i think i can't animate that myseff, i can gess, but that's not what i want. i want "precision".

i try to be more specific:
time: 0 - 250 frames.
a motor is travelling on x from 0 to 10 units in time, with acceleration and deceleration.
an object hangs on the cable of the motor: -15 units in y and is lift up in time to -8 units in y.
so basicaly, i get a 2D motion of an object flying in space.
Naturaly by the start a swing will happen and offcourse when the motor stops (frame 250) the swing will last at least for a few seconds. now i wanne know how far the swing is if i set params good like nature. (damping, mass,ect...)

this is just one example, the meaning of this is, if i setup my scene, and change a param (speed motor x, mass, travel y object,...), then i let maya calculate and see the "exact" swing.

many thanks.

[joojaa]

QUOTE(ssnovahv @ 05/04/09, 05:30 PM) [snapback]307269[/snapback]
i agree your answer if it's for animating purpose where precision is not that prior, but if i want to simulate the swing of the object who is lift up by the winch and need to "exactly" know how far and how long the object is swinging, i think i can't animate that myseff, i can gess, but that's not what i want. i want "precision".

Then its still the wrong tool. The dynamics engine does not impart real world precision kind of thing to it. So if your using this to calculate something serious you'll miss things by a mile. While simulation tools that do this do exist its a bit of a chiken egg kind of conundrum that comes up here more on that later.

Thing is maya doesn't really account for the real forces involved, it also does guesstimate things by linear moves. Maya misses one essential force here. Maya does NOT count in the inertia the mass spread of your object*, imparts to a object now in this particular simulation it WILL start to count as the resistance increases as the object traverses further. So you would still need to guesstimate this part.

IF however your object is a just a very small point shaped thing and theres no thing to adhere but magnetism, then it might work out.

This bring us to the chicken egg conundrum, wich is unfortunately if you dont know the exact maths behind the actual physics then no simulation will yield right precise results as you can not gauge whet is omitted. Unfortunately true. People often equate computer simulation with how it works in real world, but that's not what it means. It means using some model that mimics some part of some part of the system you know well. Any simulation is jsut as good as you can do yourself, youd leverage simulation when the data is too much for you to count or fluxes too often for you to anticipate the total outcome.**
QUOTE
"precision"

Either way you don't get precision. Its actually a quite easy dual integral of ahem a quick mental approximation: 2 border conditions and 3 initial values. No wait does it get back substitution, no theres air friction i hope

*not even assuming the density is homogeneous in the volume, see maya has NO VOLUME. Tahts all ok mayas not a physics simulator its a visual simulator.

**this is what I do get paid for to say most days in and out So that's free advice some people pay thousands of dollars to get me to explain it to them

[ssnovahv]

Ok Joojaa,

i learned something today: i really thought that maya was capable of doing pfysics, i'm a bit disappointed.. but: everything down side has i good side: now i just can love to make the animations that seems ok for me, try to sell them and hope that no one gets the ball against his head

allthough i will setup a system (based on the dynamics engine) that i quickly can make minor adjustments and the animation will still look nice, in the mean while i can search for a package who can do "accurate" physics.
many thanks.

[joojaa]

QUOTE(ssnovahv @ 05/05/09, 02:39 AM) [snapback]307301[/snapback]
i learned something today: i really thought that maya was capable of doing pfysics, i'm a bit disappointed..

It can do some physics but it in no way does ALL physics (because we humans don't know them all). This applies even to serious engineering simulation applications as well Its all jolly good to simulate stuff in games art 100 fps but they dont represent anything totally real. What usually is omitted is accurate firction calculations and accurate collisions. (its all fun and games afetr all, but try to put a 30 million polygon car dor to sim and suddenly it aint so fast anymore, and yes when simulating welding for a car door its thats accurate).

So simulation does not mean it does all the physics calculations it does some and its your job as a simulator to gauge what you need to account for. Mayas just about how things look so for a subset of jobs its enough to only account most easily calculated things such as collisions and force fields to create the illusion of reality. Its not meant for scientific simulation.