I CNC'ed a splined coupler that lets me mate a standard 11T or even 10T cassette cog to my White Industries freewheel. The two main reasons for making this were that I wanted to both avoid a derailleur because with horizontal dropouts it is redundant to have a derailleur AND to run a much smaller gear with a nice freewheel mechanism. It also let's me adjust chain alignment more easily and have arguably cheaper maintenance ($10 cog).
Aluminum is just a prototype.. but should work out well. I got the spline pattern very snug the first time around. The last cog on a cassette has much more surface area, so I'm not too worried about stripping the splines.
If anyone one wants one, I have the CAMing done and can spit another out in less than a couple hours, so let me know if you want to do business
. If I ever did an RC build I would easily add the mounts for 130bcd road rings...
The reason the splines have rounded grooves is that the smallest endmill I had (1/8") would not get all the material if I didn't overcut. Worked out splendidly. Again, if anyone wants one.. maybe I can make a business out of it.
Pretty soon I'll have my welder done so I can finish my pack. I just got the weld pressure sensor working, but I have yet to finalize the main circuitry.