the right in fig1 by a step equal in distance to the throw or travel of the carriage 14 because the belt flight 50 is of the same belt as the flight 48 in the illustrated embodiment obviously the flight 50 will move in the opposite direction to the left in fig2 by the same distance to initiate the next step the coils 28 and 62 are de energized while the coils 30 and 64 are energized by imposing a bias voltage on the transistors b and d in this state the carriage will be driven from the stop 18 back to the stop 16 or its initial condition while the armature 66 in the motor 48 is engaged with the flight 50 thereby moving it to the left as viewed in fig1 repetitions of this operation will advance the belt in step increments in a clockwise direction as shown in fig1 the armature 66 of the clamp motor 48 will be positioned by the iron disc 74 so that it remains in engagement with the belt flight 48 when all coils are de energized in should also be understood however that the clamp motor 58 can be made self centering by for example placing the washer 74 at the center of the motor so as to release the belt upon each de energization in fig3 of the drawings an alternative embodiment is illustrated in which components identical in structure or similar in structure but identical in function are designated by the same reference numerals but in a 100 series thus in this instance the clamp motor 158 supported by the carriage 114 includes essentially the.