http://bikemotorparts.com sells a 1 1/4" diameter steel drive roller with one-way self locking bearing.
http://bikemotorparts.com/driverollers.html
ahh yea, I thought I remembered seeing one somewhere.
Still to get decent freewheeling one would still need to raise it up off the tire requiring the rider to get off the bike, unless someone has a on the fly disengager. The pressure of a roller even a freewheeling one pressing 1/4-3/8 into the tire puts a significant amount of drag on the wheel.
Will need to look at why you want a freewheeling hub and a chain drive. Guess you want some lower center of gravity, and a way to customize other ways. Need to re-read this discussion again.
The reason is because after having many motorized bikes I have never had one that was a real breeze to ride as a bicycle. It has nothing to do with center of gravity.
Its about
not having to have a seperate bike and motorbike for me to enjoy bicycling. I believe one could have say less than a 25LB load on the back that was somewhat unnoticeable (besides the weight) when pedaling.
It should do this without slowing down for the clutch to disenagage, without getting off the bike to disconnect anything. It should be an ideal all in one, light weight solution for bicyclers. Also it should change gears somehow. haha
Also I live in mountains so I would love to motor up a huge hill and then just kill it and freewheel for a mile or two before I need the engine again,without the drag of a big chain, clutch or transmission, then pedal for a few miles (no engine)without struggling and hardly noticing anything but the added weight.
Where I live your either going up or down there is no in between.
Its asking a lot but I believe it what a true motorized bike should do.