The cab houses two motors. The top motor turns the rack-and-pinion steering via a small rubber band, so that the motor is not stalled when the steering reaches the end of its travel. The bottom motor drives two pairs of driving wheels via a differential.
Two touch switches are mounted facing upwards at the rear of the tractor. These contact the underside of the trailer when it begins to pivot in either direction. A light sensor between the driving wheels detects marks on the ground.
The Truck files:
This program tries to back the truck in a straight line, while beeping to warn any minifigs who might be standing in the way.
More photos of the Truck:
Copyright © 1998 Ben Williamson