It looks like the purpose of the mechanism in your picture is to convert the constant rotation motion of shaft #2 to the intermittent rotation of shaft #1. A common mechanism for achieving this is known as a Geneva drive.
There are several appealing aspects to a Geneva drive. If the input shaft is rotating at a constant velocity then the variation of speed of the output shaft varies sinusoidally which means that the angular accelerations of the output shaft speed up and slow down gradually before coming to a complete stop. In addition, when the output shaft is not rotating it is locked.
I am not familiar with the mechanism geometry in your picture. It looks like the ratio of the radii of the two effective "gears" is 4:1 and that one revolution of the input shaft will cause the output shaft to rotate by 45°. I think the shape of the cutout curve of the output gear is an epicycloid. I would try creating it by defining a series of points formed by rotating the input shaft by -5° and the output shaft by +20°. If you are interested I could take a stab at it when I have a little time in the next day or so. Better yet, do you think you could use a traditional Geneva drive instead?
Upon further inspection I think my previous post is all wrong!!! Please ignore it.
The mechanism looks more like some type of feed system with an impeller. Do you know what it is used for? The cutout shapes could be simple arcs. The following drawing shows how to determine the radius of the cutout if you know the wheel radius and distance between the wheel and impeller shafts.
