Thinking Particles: Scale an object down to nothing over time

This is a setup I came up with for scaling down a shape inside TP to nothing and then deleting the particle, so that the particles disappears smoothly and doesn't suddenly vanish.



Basic scene setup:

A cross point for spawning particles and a box point for the particles to travel to that also triggers the scale down event once a particle reaches it.

Method:

Once a particle gets close to the point, it triggers the start of a Timer. This determines how many frames it takes for the particle to scale down and die. The scale of the particles is multiplied by the complement of the Time Relative output from the Timer node, allowing it to scale from 1 to 0 over the timer frames. Finally there is a threshold to detect when the particle gets small enough to be sent to be deleted.

Groups:

Spawn_Trigger_Particles:
     Just one particle group. Name was left over from another TP Dynamic.

Dynamics:

Spawn_Particles:
     Particles are spawned at the cross point.

Assign_Shape:
   Shape assigned for easier viewing.

Scale_Down:
     The particles are attracted to the box point by using a BringTo. It also has a Distance condition, so that when the particle gets within a certain range using the Threshold, they start a Timer (The Timer is set to 30 frames). This is where the "magic" happens. The Time Relative output of the Timer node outputs a normalized value between 0 and 1 over the Timer range [0 at frame 0, 0.5 at frame 15, 1 at frame 30]. This is the opposite of what we want, we need a range between 1 and 0 for our scale down. To do this I created an Expression node and setup a "complement" using the following expression:

1 - a

Now this can be plugged into the Scale Factor input of a Scale node. Finally I used a Threshold node such that when the complement goes below 0.001 (an amount where I consider the particle is small enough to delete) it activates a Particle Die. It is worth noting you need to plug the Particle output from the timer node into these nodes and not from the PPass.

You could adapt this effect quite a bit as need be. You can have the time start when particles enter a new group. You could also add a Random node to the Timer Frames to get different lengths of scaling down.