when:
- R1 is different from R2
- pins radius are larger than shafts radius
- number of pins is infinite so screw surfaces are created.
The working surface of the blue shaft is created when a circle of radius 10 (in the plane perpendicular to the shaft axis, its center is 5 from the shaft axis) moves along a helix of pitch 20.
The working surface of the pink shaft is created similarly by a circle of radius 15 (in the plane perpendicular to the shaft axis, its center is 5 from the shaft axis) moving along a helix of pitch 20.
Distance between the shafts is 25.
Transmission ratio is 1. The mechanism now looks like a gear drive but the two shafts rotate the same direction.