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MAYA Problems / Questions - Seeking help

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Joe Derone
MAYA Problems / Questions - Seeking help
on Mar 31, 2010 at 1:33:33 pm


I am working on a scene in Maya, not my first, but let's say my first serious scene, I am relatively new to Maya and have watched and read several tutorials but cannot find a solution to some specific questions / problems that I have.

The Scene is an alien turret with two extensible barrels who fire alternatingly. They each fire a single particle per shot, to which a glowing "shot" deformed nurbs sphere is attached. At this time, the barrel recoils and it takes a moment before it can fire again. Now I have run into several problems, some I have been able to solve, others I am having ongoing difficulties with:

1) Instancing: I have instanced the nurbs sphere (more like a drop shape) to the particle to simulate the shot. This works fine when the turret is facing level to the ground (firing forward). When I tilt the turret upwards, the particles fire in the correct new direction (emitters are parented to the turret), but the instanced object does not fully turn in the direction of the shot. They keep facing level to the floor or even face sideways, basically being parallel to the turret.

I have tried everything I can think of: Freezing transformations, deleting history (on nurbs sphere), I rotated it and re-instanced it, I tried (but it seems impossible) to rotate the pivot point (I could not manage to go to rotation handle while in pivot mode), nothing helped. The original nurbs sphere is aligned along the X axis, facing in positive scale (initial state). The turret is firing in positive Z direction.

I have also tried every Rotation setting in the particle shape (the instanced rotation) - velocity, acceleration, force etc ... nothing works properly.

Does anyone have any ideas what else the problem could be? I am running out of ideas!

2) Particle emission

I want to set up the scene so I can later automate the "firing" of the turret as soon as an object comes within a certain range. So I wanted to keep it simple and have a "firing" boolean attribute on the turret - this is tied via an expression to the "rate" attribute of both emitters. The "firing" attribute is then turned on and off via keyframes (or in my case poses in the trax editor).

The problem I have with this set-up is that I have really big problems with getting the emitters to emit just one particle at a certain keyframe. The only way I can do this is to set the rate to 24 (since the scene speed is set to 24FPS) and immediately after (via firing attribute boolean) with above mentioned expression. If I set it to 1, it emits one particle AFTER 24 frames which is not what I want. And when you set it to 24, it emits one particle per frame so you have to turn it off again very quickly. Not an ideal solution!

Is there ANY way (ideally in MEL) to tell the emitter to emit ONE particle only at a specified keyframe, with a certain speed in a certain direction? I have searched everywhere and found absolutely nothing on this issue - how are gun shots normally simulated? Any help on this would be appreciated.

3) This may be more more of an add-on question: For the actual shots, I am used to Lightwave, where you could just parent a light with lens flare to it and set a random rotation to the lens flare to get a nice star-trek like photon torpedo-look. As far as I understand you can also do lens flare in Maya but I want to render in mental ray - and ideas? Thanks

Maybe tied into this: A lot of people in forums are saying about glow and lens flare: "Add it in After Effects" - but the light will reflect off objects that it passes by how would you do this in AE? Also, how can AE "Track" this shot to know where the lens flare should be? (As you can see I have no clue about AE - but it sounds rather unneccessarily complicated to do things in a post-processing software that could be done much better in the actual 3D Program). Or maybe I am missing a big point.

In any case, sorry for the long post but wanted to get all info in there - looking forward to any help I can get.


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Michael Frank
Re: MAYA Problems / Questions - Seeking help
on Apr 1, 2010 at 5:36:04 pm

Hey Joe,

1) Tried setting up something similar here. Best thing I could come up with was to link the original object's rotation with the emitter's rotation. The instances should update if you have the history still. I guess you might need a different object for each emitter if they have different vectors.

2) I just got an emitter to fire off one shot - by setting a real high rate keyframe, followed by a 0 keyframe. Then the particle itself I limited to Max Count to 1. And you will have to set it to have a lifespan. Once that first one is dead, another 1 particle can be born.

3) Maybe you could set up some kind of geometry. Lens flare is really just a glowing graphic shape so maybe some light emitting geometry, or surface shader would work.

I think the worflow that people are talking about is to use a piece of reference geometry as a render pass. You could render out something star shaped for instance, and use the alpha channel for a compositing effect. Have the alpha channel "lighten" or "add", create some blur around it, etc. If it has to be in reflections, it'd be trickier but might still be doable.

If you can come up with a solid workflow, it can be a whole lot easier to do things with compositing.

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Joe Derone
Re: MAYA Problems / Questions - Seeking help
on Apr 5, 2010 at 4:53:07 pm

Hey, thank you for answering!

to 1) I tried this as well, nothing worked. Since it worked when I re-created an empty scene with a box as the turret and 2 emitters parented to it, I just re-build the emitters and the instancing - now it works. Very strange.

2) I have it set up similarly, with a rate of 24 since I have 24 FPS and I keyframe it on and off - this way I don't have to make the particle die before another one can be shot. Thought there was a better way.

3) Thanks! Now I understand it a bit better, also as to why you would do it.

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