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Tyre burn out Aero. Rotation as velocoty

Message 1 of 30
3021 Views, 29 Replies

Tyre burn out Aero. Rotation as velocoty

Hello. I have to try a burn out with bifrots graph.

I want the tyre rotation affect the aero. simulation(movement)

How do I do that?


Message 2 of 30

If your tyre is set up as an emitter for the smoke you can use the inherit velocity option on the source air. Increase the inherit velocity value to make the smoke inherit more of the tyre's velocity. 



Michael Nielsen

Principal Engineer
Message 3 of 30

Thanks michael

No, the tyre itself doesn't emit. The emitter is behind the tire close to ground, it is a cube transformed.

The smoke and the tyre are closest. I set the tyre as collider, something happened but not as i want.

The setup is closest to this.



Message 4 of 30
in reply to: darioOrtisi


Message 5 of 30

Perhaps it would work to just emit velocity from the tyre with a source air node. So, set density and temperature to zero and then just use the inherit velocity option on the source air. If the velocity needs to be felt further away from the tyre, the tyre can be scaled or the geo volume offset can be set on source air.



Michael Nielsen

Principal Engineer
Message 6 of 30

I'm Lost.

I would disconnect the old emitter, using the tyre, set density and temperature to 0 and use inherit velocity of source?

But it doesn't emit nothing?

Message 7 of 30

Sorry for the confusion. No, keep the old emitter and add a second emitter that emits only velocity.


Michael Nielsen

Principal Engineer
Message 8 of 30

Hi Michael.

I have good results thanks to your helps.

I've experimenting added custom velocity, using point normal, converted to point_velocity, converted the point_velocity to levelset and using this as volume_influence on my sim aero. I've also used the second emitter with density and temperature to 0 and inherit velocity. Just a question.

The various method, e.g. speed method how works? Add, set, multiply rate, ok i can translate and understand the word, but in this case with inherit used, because the object on source air, how can this methods differentiate?


Message 9 of 30


With inherit velocity enabled, the velocity of the source affects the air/smoke velocity, and the mode determines exactly how this is done. With the add mode for example, the velocity of the source is added to the smoke velocity each time step. With the rate mode, the velocity of the source is divided by the time step and then added to the fluid velocity each time step. On the info tab on source_air all the modes are described in detail.

Hope this helps.



Michael Nielsen

Principal Engineer
Message 10 of 30

Burnout anyone?

Thanks Michael


Message 11 of 30
in reply to: darioOrtisi

Another one with more vorticity


Message 12 of 30

Woudl you like to share the graph on this one?

Message 13 of 30

Hi @Christoph_Schaedl 

I'll share asap. Let me clean up it. But i can share the graph alone or it need to be in a scene?

Message 14 of 30

If you want to add it to the Bifrost download page its better as a compound.

If you want to upload it here a scene file would be nice.

Message 15 of 30

I think I could share the scene. I'm not big fun of the compounds(that's it)

Let me clean up.

A couple of notes before share.

Maya unit set to cm.

We're usually working on Z-up Axis.

The wheel rotate on Y-axis.

The simulation run in unit scale 0.01. Because the object we're using are 100X scaled up.

I've added the cilinder animated on the Y axis as tyre.

I've added also a geometry that simulate the collider arc wheel, and also a ground that is connetced too as collider.

I think and you can confirm this, that the velocity connection i've created need a scale up. There is a port-in on the graph, i've called "VELOCITY VALUE SCALE", where you find 3 value to add, I've set them to 300, 30, 300 first becasue I want exagerates the effects and second because the velocity is taked by point_normal and i've connected a node called Rotate_by_qyuaternion and multiplied to this 3value float value(OMG how long is this phrase). Any way with this 3 value(and the value 30) i've modified the direction of the point_normal converted to point_velocity.

Without this modify, the normal direction go away as lateral the velocity. Anyway there is a visualizer point_scope bif out to see the point_normal as velocity.

It would be great to create a scene basis(rigged)

Message 16 of 30

This is the scene.


Message 17 of 30
in reply to: darioOrtisi

Here something that could be called tutorial.

Is far from professional youtubes istructor. Sorry

Message 18 of 30
in reply to: darioOrtisi


My compound have a rotate axis that work in world space. There is something that i can do to convert to object space?

I'm animate the car along a path curved. All works well but the velocity is not oriented well so the movement of the smoke is not in the correct direction.

Message 19 of 30



For an object animated on a path:

  1. Convert the local direction you want (say [-1, 0, 0] for -X) into a 4D vector using vector3_to_vector4 with w = 0.
  2. Use matrix_multiply to multiply the object's 4x4 world transform matrix with the result. The matrix must be the first input.
  3. Convert the result back to a 3D vector using vector4_to_vector3. (You have no use for the w output.)


I hope that helps,


Grahame Fuller
Learning Content Developer
Message 20 of 30

Hi @Grahame_Fuller 

I try with your hint. But iwht no success.

A syou can see from the images. The first is my normal2velocity compound

When I rotate the cilinder, second image, the normal get the orientation. I will like to follow your procedure but i think i missing something.

The third image explain the chain i've made, I'm walking in the dark right now. 🙂



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