Caterpillar track

Caterpillar tracks are large (modular) tracks used on tanks, construction equipment and certain other off-road vehicles. Unlike the rubber-made Kegresse tracks used on snowmobiles, the Caterpillar tracks are made of metal or some rigid material. The tracks help the vehicle to distribute its weight more evenly over a larger surface area than wheels can, keeping it from sinking in areas where wheeled vehicles of the same weight would sink. For instance, the ground pressure of a car is equal to the pressure of the air in the tires, perhaps 30 PSI (207 kPa), whereas the seventy-tonne M1 Abrams tank has a ground pressure of just over 15 PSI (103 kPa).

Engineering

Modern tracks are built from modular chain links which compose together a closed chain. These chain links are often broad and made of strong metal. The links are jointed by a hinge. This allows the track to be flexible and maintain its elliptical shape.

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The vehicle's weight is suspended from a number of road wheels, or "bogies". Road wheels are typically mounted on some form of suspension to cushion the ride over rough ground. Suspension design is a major area of development; early designs offered only a few inches of travel using springs, whereas modern hydro-pneumatic systems allow several feet of travel and include shock absorbers.

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Tracks are moved by a toothed drive wheel, or drive sprocket, driven by the motor and engaging with holes in the track links to drive the track. The drive wheel is typically mounted well above the contact area on the ground, allowing it to be fixed in position. Placing a suspension on the driving wheel is possible, but is mechanically more complicated. A non-powered wheel, an idler, is placed at the opposite end of the track, primarily to angle the front (or rear) of the track to allow it to climb over obstacles. Some track arrangements use return rollers to keep the top of the track running straight between the drive sprocket and idler. Others are "slack track", allowing the track to droop and run along the tops of large road wheels.

Related Topics:
Drive wheel - Sprocket

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Tracked vehicles have better mobility than pneumatic tires over rough terrain. They smooth out the bumps and glide over small obstacles; riding in a fast tracked vehicle feels like riding in a boat over heavy swells. Tracks are tougher than tires since they cannot be punctured or torn. Tracks are much less likely to get stuck in soft ground, mud, or snow, since they distribute the weight of the vehicle over a larger contact area, decreasing its ground pressure. Bulldozers, which are most often tracked, uses this attribute to rescue other vehicles (such as wheel loaders) which have become stuck in or sunk into the ground.

Related Topics:
Pneumatic tires - Pressure - Bulldozer - Wheel loader

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The disadvantages of tracks are lower top speed and the damage that they cause to what passes beneath them: they can severely damage lawns, farm fields, and even asphalt pavement. Prolonged use places enormous strain on the drive transmission and the mechanics of the tracks, which must be overhauled or replaced regularly. It is common to see tracked vehicles such as bulldozers or tanks transported long distances by a wheeled carrier such as a semitrailer or train, though technological advances have made this practice less common among tracked military vehicles than it once was.

Related Topics:
Transmission - Semitrailer - Train

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