“CATERPILLAR” TRACTION
Long ago it occurred to inventors that a machine could travel over trackless wastes if they carried their own tracks with them. The idea dates back more than a century, but only in comparatively recent times has it been developed to a practical stage. The track-laying mechanism takes different forms, but in one prominent type it consists of a series of plates linked together to form a chain or belt that passes around a series of wheels. As the machine progresses the plates are successively laid down in front of the wheels and picked up behind them. The wheels consist of a large number of rollers whose axles are spring-supported so that they are capable of a certain amount of vertical movement and as the belt they roll upon is made up of separate plates they can adjust themselves to irregularities of the ground and creep over an uneven surface. Its close resemblance to the creeping locomotion of a caterpillar has led to the adoption of the trade name “caterpillar” by one of the large tractor manufacturers. The tractor belt is driven by spur wheels at each end and the rollers serve merely to distribute the weight of the machine along the belt. The traction is exceedingly great because the belt is broad and long, giving it a large gripping surface. For the same reason it will not sink into plowed ground. Because of its flexible tread surface it will creep over rocks and stumps, waddle down into a ditch and climb up the opposite bank. So powerful is it that it will crash through underbrush with ease and even small trees yield before it. It will run over soft mud, deep sand, and even snow with equal facility. The tread belts on either side of the tractor are separately driven and by making one belt run faster than the other it is possible to steer the machine. In fact it can be made to turn around in its own length by stopping the belt on one side and driving the belt on the other.
Such a machine is ideal for plowing and other are hauled with ease over the soft plowed ground. For ordinary farming purposes speed is not essential, but the possibility of rapid travel with tread-belt traction was demonstrated in the World War when small “tanks” were built which could run at the rate of twelve miles per hour.