A tracked vehicle (also called: track-type tractor, tractor crawler, or track-laying vehicle) is a vehicle that runs on tracks instead of wheels. Typically used as part of an Engineering vehicle once additional attachments have been added.
The principal design advantages of tracked over wheeled vehicles are that they are in contact with a larger surface area than would generally be the case with a wheeled vehicle, and as a result exert a much lower force per unit area on the ground being traversed than a conventional wheeled vehicle of the same weight. This makes them suitable for use on soft, low friction and uneven ground such as mud, ice and snow. The principal disadvantage is that tracks are a more complex mechanism than a wheel, and relatively prone to failure modes such as snapped or derailed tracks.
A long line of patents disputes who the "originator" was of this concept.
Alvin O. Lombard of Waterville, Maine
was issued a patent in 1901 for what appears to be a regular railroad steam locomotive
with sled steerage on front and crawlers in rear for hauling logs in the Northeastern United States
. The haulers
allowed pulp to be taken to rivers in the winter. Prior to then, horses could be used only until snow depths made hauling impossible. Lombard began commercial production which lasted until around 1917 when focus switched entirely to gasoline
powered machines. A gasoline powered hauler is on display at the Maine State Museum in Augusta, Maine
After Lombard began operations, Hornsby
manufactured at least two full length "track steer" machines, and their patent was later purchased by Holt in 1913, allowing Holt to be popularly known as the "inventor" of crawler tractors. Since the "tank" was a British concept it is more likely the Hornsby, which had been built and unsuccessfully pitched to their military, was the inspiration.
In a patent dispute involving rival crawler builder Best, testimony was brought in from people including Lombard, that Holt had inspected a Lombard log hauler shipped out to a western state by people who would later build the Phoenix log hauler in Eau Claire, WI, under license from Lombard. The Phoenix Centipeed typically had a fancier wood cab, steering wheel tipped forward at a 45 degree angle and vertical instead of horizontal cylinders.
In the meantime a gasoline powered motor home
was built by Lombard for Holman Harry (Flannery) Linn of Old Town, Maine
to pull the equipment wagon of his dog & pony show, resembling a trolley
car only with wheels in front and Lombard crawlers in rear. Linn had experimented with gasoline and steam powered vehicles and six wheel drive before this, and at some point entered Lombard's employment as a demonstrator, mechanic and sales agent. This resulted in a question of proprietorship of patent rights after a single rear tracked gasoline powered road engine of tricycle arrangement was built to replace the larger motor home in 1909 on account of problems with the old picturesque wooden bridges. This dispute resulted in Linn departing Maine and relocating to Morris, NY, to build an improved, contour following flexible lag tread or crawler with independent suspension
type, gasoline and later diesel
powered. Although several were delivered for military use between 1917 and 1946, Linn never received any large military orders. Most of the production between 1917 and 1952, approximately 2500 units, was sold directly to highway departments and contractors. Steel tracks and payload capacity allowed these machines to work in terrain that would shred or cause to spin the poorer quality rubber tires that existed before the mid 1930's.
Linn was a pioneer in snow removal before the practice was embraced in rural areas, with a nine foot steel v-plow and sixteen foot adjustable leveling wings on either side. Once the highway system became paved, snowplowing could be done by four wheel drive trucks equipped by improving tire designs, and the Linn became an off highway vehicle, for logging, mining, dam construction, arctic exploration, etc.
Once steel cleats became unpopular on paved roads, in 1938 a limited experiment began to bridge the gap between truck and tractor, a "convertible vehicle" patented by Phillip Sloan, the C5 Catruk, suffered design flaws and limited production before it was finally abandoned.
Fate of pioneer companies
Lombard gasoline production was more limited as they never managed to diversify use away from log hauling; it is believed a diesel built in 1934 was their last unit.
Phoenix, Eau Claire, Wisconsin, appears to have built at least one gasoline powered machine before fading into history.
Holt and Best ended up merging. Holt had registered the trademark Caterpillar. They merged company produced a version of the Best 60 tractor, which later became the Caterpillar 60. The new corporation Caterpillar Inc. took that name about 1925, and remains in business today.
- The crawler tractor was the basis of the first designs of tank.
- Crawlers equipped with a shovel like blade are called bulldozers, and used for construction and earthmoving projects.
- Crawler design have been intermittently popular for farm use.
- The space shuttle is transported to its launch site by a large Crawler-Transporter.
- The largest crawler in the world is the German bagger 288 excavator.
Types of tracks