Trail Dust Depending Of Velocity

[rentboy]

hello there,

I have a car which is riding on the desert, and I need to create a trail dust. this car is going to be use in different shots. therefore we are thinking to create some particle emission depending on the car speed..

the emission rate would have to be linked to the car's velocity so it doesn't emit when it's not moving, and emits less when it's moving slowly?..

Does anybody knows or has and idea how to achieve this type of effect?..

cheers.

rents

[kmannens]

Have a look at my Scaling emission rate based on emitter speed, found here:

http://www.tokeru.com/t/bin/view/Maya/MayaParticles

[chartt]

Okay,

Can you find out the speed of the car? You could do it with kmannens' link - by creating a particle and storing its position at the frame you are on along with the previous frame. - Good way to go. If you have a group node for the entire car, you can do it with the translation of the this node in the same manner ->
get its position,
store it in a variable,
get the position on the next frame,
store position again
subtract the two
take this answer
mag(result) to get the speed.

Then based on this delta (change in speed) you can use a linstep function as a multipler to the emission.

emission.rate = lowest_emission + base_emission_rate*linstep(lowest_emission,highest_emission,actual_speed);

Chris

[fxnurbs]

and why don't you just use key frames manually. Particles are quiet tricky to behave. A simple on and off will probably give you issues. That's not a big deal to work that on a separate workflow that you control precisely ?

well, i just wonder

PS: a little trick that i used in a commercial once and worked pretty well :
for a trail in a desert, i used a fluid cloud with just a translate expression in the billow texture. I made it large to be able to roto gently the clouds shapes and with 2 or 3 layers in comp it was perfect. And no tricky heavy dynamic simulation.

I must admit that for a long shot you can have issues, but it could help

cheers