Vitamin Reduction - Polar Stage Combined with Z axis

This is a concept I came up with today as a possible way of reducing the number of the most difficult to source and expensive reprap vitamins in a future subspecies. It would unfortunately require a switch to a polar coordinate rather than a Cartesian robot, which has been discussed and discarded before. At any rate, the design works like this:
1)The build stage is set up as a very large gear, and a stepper motor drives it with a small gear from the outside. This gives it the high resolution required for a polar/rotary machine.
2)At the center of the rotating build stage, it extends downward into a gear, which serves as the primary or "sun" gear of a planetary/epicyclic gear train. The ring gear is a part of the stage to which the stepper is attached. This whole stage is supported from the center by a threaded rod, which is attached to the output of the planetary gears (a ring which is connected by bearings to the planet gears, so it rotates once when a single planet gear makes a complete circuit of the ring gear. This provides an extreme reduction between the polar stage and the coupled Z axis, so that a single layer of building can be accomplished within a fraction (say, 1/10 or 1/20) of a layer height of variation.
3) descent to the next layer is accomplished by rotating the build platform multiple times. Tip cleaning can occur during this phase, with a cleaning rig (clip/toothbrush) set at a point on the outer edge of the platform that has too low a resolution for build use.

The advantage here for vitamin reduction is pretty clear. Fewer steppers is the holy grail of vitamin reduction, of course, and that's the biggest thing going on here. The planetary gear system is also more amenable to replication than belt systems. The ring and build stage gears could in theory be broken into parts for printing, and the planet gears would be trivial to print. The Sun gear could be printed in one part, centered on the center of the polar axis.

I don't believe I've seen this particular concept around the forums or blogs before, but I've been wrong before. Let me know what you think. Crappy sketch included for your entertainment.

Nice idea. one motor drives the rotation axis and also the z-axis at a massive rate of reduction.

So, when printing a minimug, you will have 1 platform rotation height difference between the start and finish of the outer wall.

To make this height difference minimal, you will have to gear the z-axis down by a lot - say 100 - which will give you a 1% difference in layer height between start and finish. (unless you're printing the spiral boxes!)
Difficult area: z-axis movement will require a *lot* of rotations - e.g. a 100-layer print will need 10,000 revs to build, and another 10,000 revs to home again - with a stepper that's already geared low for accuracy on the polar axis.
It might take a while?

Difficult area: filament speed is no longer constant, but now highly dependent on position, so you'll need good extrusion control (0 at center to max at outer radius), and some neat speed control to get good prints.

Bonus : Since the resolution varies according to the radial distance, small objects get a better accuracy for building!

Good luck!

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