The crane was built around a triangular structure. It now contains the servos, an electronics junction, left and right boundary switches, and a barcode scanner.
It splits the fat cable from the main board to the crane and a smaller cable to the sled.
Two servos move the sled up and down.
The crane is locked into a J shaped track. This is the most stable method and keeps it from needing a counterweight.
Horizontal movement is powered by a bidirectional winch. Only a bidirectional winch can provide movement over the vast distances required. The bidirectional winch is attached to the cable at both ends and can pull in both directions with a single motor. The key is a set of weights which keep the cable under tension at all times.
Many early barcode attempts. The crane uses barcodes to know where it is and align exactly with each tower. 4 bars encode the tower number. 1 bar aligns the crane with the tower. A fat bar is a 1 and a thin bar is a 0.
The final barcodes were laser printed and held down by a screw.
The crane reads barcodes with a laser bounce sensor. Normal movement of the crane passes the sensor over the barcodes.