(hit the 2x)
I received so many E-mails about the last post with questions about how it was done that I thought I'd post a separate shot with the particulars. This will be of more use to Blender users, but there are some general answers too.
Q: What software did you use?
A: Blender (blender.org)
Q: Did you light it using an HDR?
A: No, just a bunch of emissive surfaces.
Q: How did you figure out the gear timing?
A: Google "planetary gear ratio" -- there are plenty of formulas, depending on what planetary gear mechanism you want to implement.
Q: How did you design the gear geometry?
A: The 2D cross-section of these gears is a "spur gear", like the gears in legos. Google "gear geometry" and you'll find lots of step-by-step guides. Once you have the basic geometry, you can use "loft-rotate" or "twist" (depending on the software you're using) to get the helical shape.
Q: The material used on the gears reacts oddly to light. Why?
A: I'm attaching a screenshot of the shader setup I used to this shot.
Q: How did you get those light rays to shine through the gears?
A: In this particular case I used the blender compositor to combine a couple of separate renders. This really depends on what software you're using, some renderers will be able to give you this effect in a single pass.
Q: How did you composite this scene?
A: I'm attaching a screenshot of the compositor setup I used to this shot.
If you have any additional questions, post them and I'll try to provide useful answers.