View Full Version : Speed by icon and physx

08 August 2010, 04:52 PM
It was a long time i didn't post asking for you. And now, I need you.
This is the story : you will se in this video ( a scene with a spline and a speed by icon moving along this spline. I have a shape instance. I put physx to have dynamics between the particles and also to have collision with the blue box. Without physx, i have the following line shape. But, i need physx to have collision between these shapes and also with the blue box. You will see in the video with the physx, objects don't follow the line. Why? Any idea?

I hope you understand my problem.
I'm open to all proposals.
ParticleView_SpeedByIcon_WithPhysics.jpg (

08 August 2010, 05:28 PM
PhysX Switch is your friend, anytime you want to use external non-PhysX influences on your particles just add a PhysX Switch and enable the attributes to wish to control, in your case speed.

08 August 2010, 09:01 PM
Thank you JohnnyRandom for your help. I have used physx switch and it worked. But now, as you can see on image "ParticleFlow_SpeedByIcon_WithPhysx02a.jpg", shapes pass through the blue cube. Without physx switch, the collision with the blue box worked. With physx switch, we have the shapes that follow the speed icon but we haven't got the collision with the blue box.

Any idea?

ParticleFlow_SpeedByIcon_WithPhysx02a.jpg (
ParticleFlow_SpeedByIcon_WithPhysx02b.jpg (

08 August 2010, 11:16 PM
Is the "Box" Pflow Collision Shape modifier Activated? It looks like it is off to me. At least that is the behaviour you get when it is off.

08 August 2010, 11:54 PM
Yes, The pflow collision shape modifier is activated. Why it does not work? Please, help me !

09 September 2010, 01:48 AM
if you uploade the scene we can have a better look :)

09 September 2010, 07:56 AM
PsychoSilence, you will find a zip file with the scene. Thank you in advance for your help. (

09 September 2010, 10:38 AM
I'm no box 2 expert, but I think the speed by icon overrides the physx

09 September 2010, 02:28 PM
Glacierise : Maybe the speed icon overrides the physx and maybe there is another solution without the speed icon to animate particle follwing a spline and with physx? Actually, i don't know what is the problem. I'm searching and i hope CGtalk will help me to find the solution.

09 September 2010, 03:18 PM
Allright, made a coupla changes in your scene, that was easy :)

first of all there was another particle system to the right of your flow that had a different physx world all together! That was not part of your problem but you should only have 1 physx world in your scene ever, you can instance the one world operator the physx flow creates around as much as you want into other events to share the world.

second your viewport substeps where different from your render substeps. i made both viewport and render half frame now, that should do in your case. make it 1/4 frame if necessary or more.

i substituted your birth operator and position icon with a birth stream that comes with box2. birth stream is a position icon, speed operator and keep apart in one operator! this is so physx driven particles dont intersect at birth to cause the "physx explosion".

your physx shape was pretty tiny so it was not surprising to see some particles slip through. i changed the collision shape from BOX to CONVEX HULL and changed the "Inflate Width" from the default of 0.01 to 0.6 since your disc are flat. this inflates just the collision shape as the name suggests. your render shape is still the old size.

and lastly i arranged your operators around a bit they make more sense visually. i usually like that in my own flows. Like have it arranged BIRTH > POSITION > SHAPE > BEHAVIOR > DISPLAY / TEST, but thats just me :) I activated the spin as well and checked match spin in the physx switch.

Have fun! Your setup was 90% there already :)

file attached is max2010

kind regards,

09 September 2010, 04:23 PM
Thank you very much. Your advice will be very useful to me. thank you again and if I can help you one day, I will (you never know ;) ).

10 October 2010, 02:42 PM
Thank you so much! It is my first time to Learn it!

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