screw 89 the annular housing 88 has an open end for admitting an electromagnetic energization coil in the form of an annular ring 90 the energization coil 90 is fixed to any suitable mount e g the end plate 18 the coil 90 is spaced from the interior walls of the annular housing 88 to permit rotation of the housing 88 with the drive shaft 42 the housing 88 is spaced from the pulley 24 and has a plurality of drive teeth 91a facing a similar plurality of drive teeth 91b on the pulley 24 the drive teeth 91a and 91b are provided for effecting a positive drive of the pulley 24 by the housing 44 and to provide discrete repeatable positioning of the pulley 24 on the other side of the pulley 24 is located a second annular housing 92 which is arranged to enclose an energizing coil 93 therein the second housing 92 is fixed to any suitable means e g the side plate 18 to prevent rotation thereof while allowing the drive shaft 42 to pass through a central opening in the annular housing 92 bearing means 94 are provided between the shaft 42 and the annular housing 92 to allow the shaft 42 to rotate independently of the annular housing 92 the pulley 24 is also provided with a bearing means 96 for enabling the pulley to rotate on the shaft 42 while enabling a transverse motion or movement of the pulley 24 on the shaft 42 to be induced therein by either the clutch 44 or the brake 46 thus the pulley bearing means 96 may be any suitable type of bearing e g a sleeve bearing or a ball bearing capable of allowing a rotation and a.