nParticle emit from another nParticle (how to control)

[shurik_spb]

Hi. I'm a newbie on this forum, used to be a readonly member. But today I need few advices from advanced CG artists, if they don't mind to help me
 I have a simple nParticle simulation. It creates an asteroid field. I've used this video tutorial as a reference: https://www.youtube.com/watch?v=ZKR0\_JroHfI
Thanks to its author, I know about expressions a little bit more than nothing.  
  I have an idea to emit new particles from existing emmiter.The first problem is that I can't make the new particles to inherit velocity from first emmiter.The second problem/question - is there any chance to tweak those particle shapes a little bit to make tails wider at the start of their life and thinner at the end?
Thanks!

here is a scene example  Maya 2012 binary.

And this is an example of what I mean: 

[chartt]

Hi Alex,

The velocity is fairly straight forward to get.

You need to capture the original particle's velocity.
Then you need to transfer it properly to the emit command.
Maya is silly because velocity is a vector and the emit uses a floating point array - not a vector.

You create a floating point array:

vector $vel = velocity; string $emitcmd = "emit (blah) -v $vel.x $vel.y $vel.z (blah";
eval($emitcmd);




That's a start.Width at emission....  you could start with an offset on the emission.Then apply a volume axis force (VAF) that the particles enter - that follows whatever abject that is emitting, and make your away from center a negative value - so that the arrows point inward.  Stratch the VAF out so that the end or where you want your particles to come together is the center of the VAF - use attentuation to control how fast it comes to the center.C