I have an ac motor that controls the up - down motion of the platform for a Treadmill, exercise machine. It uses a pair of triacs to control each direction. The front triac is an opto-isolator and that controls a gated triac for the 120 v windings. The motor has 3 leads: common, cw and ccw. Of course, this is a special type of ac motor designed to run bi-directional.
Pj