An open top swing assembly comprises a frame (10) which provides an open top structure and a trapezoidal shaped front base (14); a swing drive mechanism (100) includes a drive sleeve (110) rotatably mounted to an axle (32) that operatively supports the hanger, a drive flange (120), a drive flange coupling device (130) positioned between the sleeve (110) and drive flange (120); the coupling device (130) includes a hub member (140) coaxially and rotatably mounted on the axle and at least one torsional spring (134); a crank (150) driven by a motor (160) is linked to the sleeve (110) to oscillate the sleeve; a swing height control device (200) can have a sensor (210) for detecting the swing height or amplitude. The control device (200) outputs either no voltage, first, second, and third predetermined voltages to control the voltage input to the motor based on the selection of the swing height setting.