I first started playing with CVTs when I was designing the first drivetrain for my bike.  At the time I only knew of the variable sheave and cone types.  I designed a rubber belt variable sheave transmission to go with the EV Warrior motor (see picture in the Bike page) and spec'ed all the components.  After that I decided to abandon it, realizing how much more complex it is, how much time it would take to make, how much money it would cost me and how much less efficient it would be.  I stayed with single ratio drive, but later redesigned the whole drivetrain with a 2 speed mechanical transmission - efficient, simple, light, guaranteed to work. 

    A few months ago I stumbled on another idea on the web and thought it might work great for a bike with a unique spin of my own.  This is a concept of a highly efficient direct mechanical CVT (no friction devices).  The pictures show the resulting prototype that I tested on a beater bike.  I'll have to admit this particular one has a problem which I know the solution to, though to be honest I'm too busy to pursue it right now.  But who knows, maybe every bike in the future will be equipped with one of these or a variant.  The funny thing is, it's not even all that complex.  It is no more complicated than a normal manual transmission - just very different.  A simple idea...