Help with particle explosion

[mettam]

Attached Files particleInstancerExplode.zip
That expression was just to intialize the rotations. In an explosion like this the particle tend to self collide at the start frame which gives them randomized rotations and rotational velocities. However with that expression you could really make them spin fast (or not spin at all) if you wanted. The angularVelocity is the rotational velocity. If you wanted the particle to stop rotating on collision totally you could do stuff like making the angular velocity zero.

This is awesome Duncan !! Thank you.
The thing that isn’t awesome is I am not able to view the expressions, is it because you created this in 2014 and I have 2013 ?

[Duncan]

…I am not able to view the expressions, is it because you created this in 2014 and I have 2013 ?

Oh… somehow I must have deleted that expression… its not in the scene( the self collision at the start emission will cause rotations, anyways).

At any rate here it is…(a creation expression):

float $s = 2.0;
angularVelocityPP = <<rand($s),rand($s),rand($s)>>;

[mettam]

Oh… somehow I must have deleted that expression… its not in the scene( the self collision at the start emission will cause rotations, anyways).

At any rate here it is…(a creation expression):

float $s = 2.0;
 angularVelocityPP = <<rand($s),rand($s),rand($s)>>;
 

I think you didn’t write any expressions for this effect? It’s all achieved by plugging in and tweaking existing nParticle attributes, correct ? I say that because I can’t see any custom expressions.

[Duncan]

That’s right… no expressions needed. The expression is just to show how one can control the rotational speed. Particles automatically rotate on collision and self collision. The particles have rotational velocity at the start even without that expression because they are in self collision at the start frame. A limit with using the built in rotation feature is that collisions are spherical only and don’t use the geometry of the instanced object.

[Duncan]

Also you asked about stopping secondary particle emission when particles stop moving. Probably the best is to control the emission rate based on the speed of the particle so when they stop moving they stop emitting.

Select the secondary emitter and do nParticles:“Per-Point Emission Rates”. This will create a per particle attribute with the emitter’s name on the first particle system. You can then do a runtime expression to set emission from velocity:

float $rate = 2.0;
emitter2RatePP = mag( velocity ) * $rate;

[mettam]

Thanks Duncan for your previous responses, very help full indeed.

In the Instancer (Geometry Replacement) dropdown I have selected Scale/radiusPP I thought this would make the Geo scale match the diameter of the particle ?
See the attached image: Is there a way to make the size of the Instancer Geo match the particle size.

[Duncan]

It should work to select the original instanced object and just scale it.

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