Input: the pink roller, rotates counterclockwise.
Output: the green roller.
The orange ring contacts with the two rollers under its weight.
The friction forces at contact places are regulated automatically.
The blue roller of low friction coefficient material is for supporting the input and output rollers only (not for torque transmission).
The transmission is possible if tg((a+b)/2) is less than m.
a is angle CAB, b is angle CBA
C is the ring center.
m is friction coefficient of roller materials in contact with the ring (the smaller one)
Transmission is impossible if the pink roller rotates clockwise.