The green and orange wheels of Archimedean grooves are identical. The green one is input.
The pink pin slides in both grooves and in a straight slot of a fixed bar.
If the bar is perpendicular to the line connecting axes of the two wheels at its middle point, two wheels rotate in opposite directions with the same speed, like in a drive of two equal gears.
In case not at the middle point, the orange output wheel has irregular rotation.