ok, so we were on the same page. and the cost of a sprocket would be a lot cheaper than the cost to fabricate it all, unless you have access to all of the equipment and the time.
now, in order to make it shift, you would need to make a front derailler with the capability of movement the same as a rear one. then you would have to attach that to the bike somehow, too.
you'd need to have the gear selection on the wheel drive, and leave the engine drive static (one speed.)
the chain size would be a bit of a problem, as you would have to use a chain that's wide enough for the rear sprocket, yet still small enough for the cassette gears and the derailler. might be able to use a heavy duty bmx chain, i forget the size, it'll fit on the sprockets, but you still might have to modify the derailler. most derailler chains are thinner.
still, all of this could be done.
next, you're saying the cassette's freewheel would act in the same way as a bearing. it'd be like a "one way ratcheting bearing" (i just made that term up, i think
) you'd have to have a hub with a strong enough cassette so it wouldn't get ripped apart while shifting. i don't think a regular hub's freewheel would hold up.
also, if i understand correctly, the freewheel is basically acting as a bearing, the cassette as an axle, and the hub as the housing.
i don't think the cassette could withstand the constant hi speed spinning and torque loads the engine would put out. they're designed for coasting at relatively slow speeds, and all those tiny little bearings would probably fuse together or explode if ran at a constant high rpm, like a 40+mph motor bike would put out. even a 20+mph would probably melt it.
also, i'm not putting your idea down, just going through the basic mechanics of it to see if it would work.
unless i'm missing something, the middle gears would cancel themselves out, and be nothing more than a very complicated chain tensioner, unless you could make it shift.
