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google for "four bar linkage crank rocker" and you're gonna need a flywheel on the rotating side. For some definitions of intermittent rotary motion.

If you're ever bored, look at what four bar linkages can do. Stereotypical mech eng topic where its shocking just how many different things four chunks of metal and some bearings can achieve. A really poor analogy would be its kind of the turing machine of the mech eng world in that it can seemingly do almost anything with a minimal amount of parts.

There is an interesting scaling effect where the math for linkages scales pretty scarily as the number of bars increases.

(edited to add, and you can see an applied model in some stair stepper exercise machines where the arm actually moves thru an arc, which I guess is the intermittent rotary motion you're looking for?)

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