Propeller Disk problem with Mental Ray

[kevjon]

Hi

I've been trying to get a decent prop disc with Mental Ray. Just wondering if it is possible as I've had no luck so far.

I've used Arch & Design Material. Inserted black bitmap in the diffuse color for the color of my prop and then use photoshop radial blurred prop bitmap in the cutout slot which is white motion blurred prop on black background.

When rendered I get the grey parts of radial blurred prop image lighting up see attachment.

Anybody know if there is a way to create a shader with MR that will give me a nice prop disk ?

[moid]

I'm not sure about why the A&D shader is causing this although my guess would be something to do with reflections. The effect you want can be easily made with a standard shader though. Make the diffuse a dark colour or use a bitmap. Place the opacity map you made into the opacity slot. Copy the opacity slot into the specular level and go into the bitmap properties and reduce the output value to 0.2 (or better yet draw your own specular map that is dark with occasional light rings in it). This should work I reckon...:)

[kevjon]

Thanks moid.

What you suggested with a standard material works perfectly but gives me the same result as the render above. Both A&D material with cutout and standard material look correct in the material editor but when rendered with MR give the white areas around the prop.

I have a self illuminated skydome around the scene to provide reflections to my aircraft. On the prop disk geometry I have turned off "visible to reflections and refactions" but that didn't make any difference when rendered with MR. I have just discovered that when I hide the skydome the prop renders correctly with either the A&D material or standard material. This problem has held me up for weeks so at least now I have found a easy solution.

Just out of interest here is the aircraft I'm working on and now that I have found a solution to this I can move forward to some final renders.

[moid]

Aha! The prop disk geometry is not the one to make invisible to reflections / refractions, it is the skydome! Although that will prevent it from reflecting in any geometry and you probably want that on the glass. My solution would be to use the standard material, place a falloff map in the refelction slot, set it to Fresnel, then place a Raytrace map in the white slot of the falloff map. Inside the raytrace map is an exclude function, click that and choose to exclude the skydome from the material. Now everything should render and be fine:D Also if you go back to the falloff map you can increase the reflectiveness of the prop by increasing the IOR value, decreasing does the opposite but don't go below 1.0

Hope that fixes it, nice plane model.

[kevjon]

Thanks Moid.....your right. I chose the wrong object to exclude from reflections. Wasn't thinking about logically...Doh.

You really know your materials, your suggestion for the prop disk material sounds great, I'll give that a go as I've always had a hard time getting good speculars into the prop disk.

Thanks for your advice...it is much appreciated !