This is my 1st post, I have lurked, read and learned a lot, as this was all new to me, thank you all!
I am now also interested in building a grinder with a large conical burr set, most likely a powered grinder. After looking at some designs, from HG one, Versalab, to the ones on the German and Swedish coffee forums, I am now at the point where I am thinking what I want to build.
Are there any designs that spin the bottom burr and keep the smaller burr stationary? Imagine for example a HG one where the bottom part spins and the shaft holding the top burr remains stationary.
Would such an arrangement have a influence on the feeding of the beans into the burr set, in other words make it more or less likely to feed into the burrs? Would it matter if we are talking of the effect at low speed say 100 r/min or at 500 r/min? Any inputs on this will be appreciated.

No designs exist. I don't see a problem at any speed a grinder with similar burrs works. From my thoughts, spinning the outer burr seems more complicated. But, there are so many ways to go about building a grinder, follow your heart!

Getting the lower burr to spin and still having a chamber for the grounds is going to require way more complexity/cost and increase the size of the grinder.

Making for a compact less complicated design, especially the adjustment is actually the reason im considering it. Obviously the chamber with the coffee rotates with the outer burr. My conscern is that it may perhaps slow the feeding of the beans into the burr, due to the possible effect of centrifugal forces.

Doing it this way, the lower outer burr needs not be adjustable, but simply spins with its holder. The adjustment is then done by screwing the stationary inner burr up or down, requiring a much smaller screw than the normal 90 to 100mm cylinder with threads cut into it, which might possibly become full of coffee dust like I would expect to happen on the Swedish grinder.

I just can't picture how the lower burr rides on any kind of strong bearing surface without requiring a large amount of the lower chamber to turn with it. Also, would it be driven by gear teeth surrounding the lower bearing and then another smaller gear hooked up to that? You end up offsetting the motor assembly to the side and increasing the footprint.

Also, you still need a substantial shaft for the inner bearing so that it is rigid and kept in alignment.

If you wish to spin the lower burrs, perhaps a flat burr may be preferred over a conical?