Counterrotating cam and follower apparatuses (C-CAFA) capable of converting reciprocating to rotational motion, and visa versa, utilizing counterrotating cams cooperating with at least one reciprocating cam follower. Apparatus cam counterrotation is ensured to be synchronously timed without necessity of prior art stationary geartrains, by and through apparatus cam follower(s) combining with counterrotating cam surfaces acting as moving follower constraints, provided that disclosed structural limitations, including those regarding cam and follower surface interface engineering slop, multiple degree of freedom cams, rotating and reciprocating follower(s), and electromechanical limitations are met when specified. Optional apparatus usages include reciprocating mass balancer, differential to reverse and or multiply shaft rotations, and apparatus combinations with connecting rods, pistons, cylinders, and or engines. “Adequacy of Constraint and Newtonian Force Analysis, Cam and Follower Surface Kinematical Analysis, and Electromagnetic Cam Analysis” are applied to various disclosed embodiments to teach making, using, and correlation of disclosed apparatus structure to function.