a pivoted detent or pawl 43 having an outstanding tip 47 engageable with the microswitch button 45 a which can best be seen in fig7 on referring to fig7 it will be seen that cam wheel 46 has two radially elevated surfaces 48 and two radially recessed surfaces 49 when the cam wheel 46 rotates ninety degrees the positions of those four surfaces are reversed as illustrated by the phantom lines in fig7 the direction of rotation of cam wheel 46 is shown by the arrow in fig7 it is to be noted that each time detent 43 moves from a higher point x to a lower point y the microswitch 45 is thrown or tripped each time the switch is thrown current to the motor is cut off and the motor 39 stops this power cut off occurs each time the gear reducer output shaft 36 rotates ninety degrees in the embodiment shown the motor 39 is provided with a brake assembly 60 as shown in fig9 the motor 39 is mounted between the gear reducer 44 and mounting plate 62 by bolts 64 which pass through and by means of spacers 63 and 65 locate the motor core 42 the motor core includes an opening 67 in which the motor armature 66 rotates by virtue of the motor shaft 68 mounted between the gear reducer 44 and the mounting plate 62 as.