Thanks for the generous comments ;^) Miles - I'd say any ratio you want between 10 and 20:1 is pretty easy. Spinningmagnets - what I like is how accessible it is - I made that in a fortnight by walking down to the local laser cutting shop with a pen drive in my pocket with dxf's on it, bearings off the web & an hour or two on my lathe. A spur or planetry gear would need more than one stage to get that degree of reduction and is an expensive technology way outside the scope of the amateur tinkerer. I'm fairly happy with it; I don't think the mk1 is a practical solution;- too much metal flying around too fast... but I think the mk2 will be. And the way the whistling input and wobbly chain motion translates to such a smooth slow output drive is, well it's just cool!