I'd like to share the final scene file of my physics-simulation-based marble machine animation, in case it is useful for others to dissect and learn from. You can see the rendered animation I made of it here:
The scene contains 56 balls, 32 constraints, 10 drivers and exactly 2 keyframes (on the big gear's parent empty). It uses the bullet engine for the rigid body physics work. The simulation potentially could continue forever: at one point I had it going for 2000 frames without a hitch, but at some stage an adjustment I made, meant that the stairs would occasionally lose a ball. Ouch! Ah well.
I was especially interested in simulating small objects 'to-scale' to avoid that 'slow-mo' look that a lot of simulations get, when the scale and timing have to be fudged. These balls are 16mm in diameter, and using 240 steps per second in the rigid body world settings, they simulate pretty realistically and stable. If you're interested, I'm happy to share the sprawling .pdf document that was the journal/notebook I kept as I was creating this monstrosity. It includes lots of sketches and ideas, as well as prototyping and test results from when I first planned on making this in Maya, and goes into some detail about why Blender was just better :) The document is not designed as a tutorial by any means, but might be useful if you're exploring this area. Just PM me and I'll share it with you.
The file includes several excellent CC procedural wood materials by Dale Cieslak available here on Blendswap, as well as an HDRI from the CC-attribution sIBL archive "Factory Catwalk" http://www.hdrlabs.com/sibl/archive.html. The Steampunk/Lovecraftian pressure gauge texture is based on an image shared by Herbert West at http://herbertw.deviantart.com/art/Metaphysical-Gauges-335601199