Earlier I was trying to explain what I built a couple of years ago. When you look at this pic, try to imagine it mounted to the rear as you would mount a rear rack or carrier, I'm not sure of the proper name. If you were to turn this upside down, the bike would move forward as it turned your bike wheel.
All it takes is a couple of hours work, a drill, two metal pipes or tubes that mount to the wheel nuts and a hacksaw. The air pressure can be adjusted to get the right pressure so that the drive wheel turns your bike wheel without EVER spinning in place. Rubber on rubber is by far the best "friction drive" you will ever come across.

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