Tractor
A tractor (from Latin trahere) is a device intended for drawing, towing or pulling something which cannot propel itself.
Most commonly the word is used to describe a vehicle intended for such a task on some other vehicle or object.
Farm tractor
The most common use of the term tractor is for the vehicles used on farms. The classic farm tractor is a simple open vehicle with two very large driving wheels on an axle below and slightly behind a single seat (this and hence the steering wheel are not on the left or right but in the center) and the engine in front of the driver with two steerable wheels below the engine compartment.
There are usually three pedals on the floor of a tractor, right below the steering wheel. The pedal on the left is the clutch, the operator presses on this pedal to disengage the transmission for either shifting gears or stopping the tractor. The two pedals on the left are the brakes. The left brake pedal stops the left front and rear tires, and the right break pedal does the same with the tires on the right side. This provides another method of steering the tractor, this is usually done in situations where a tractor needs to make a tight turn. The operator would press both pedals at the same time to stop the tractor.
The throttle, unlike those in automobiles is generally controlled from a hand operated lever. This helps provide a constant speed in field work. It also helps provide continuous power for stationary tractors that are operating an implement. Some modern tractors have an additional pedal on the floor that serves as an additional throttle control, giving the operator more control over the speed of the tractor.
Most farm tractors use a manual transmission. They have several gears which generally provide a range of speeds from less than a mile per hour up to about 25 miles per hour. Compared to other vehicles, the tractor is quite slow. Slower speeds are necessary for most operations that are performed with a tractor. These slower speeds help give the farmer a larger degree of control in certain situations - such as field work. Older tractors generally require that the operator press in the clutch to shift the gears, but some modern tractors can shift between gears without the need to depress the clutch.
The farm tractor is used for pulling agricultural machinery or trailers, ploughing, harrowing and similar tasks. Modern farm tractors can be quite large with eight driven wheels, four on the front axle and four on the back axle, and articulated steering. Variations of the classic style are used for smaller farm tasks, mowing grass, and landscaping.
The size - especially with modern tractors - and the slower speeds are one of the reasons the government urges motorists to use caution when encountering a tractor on the roads.
Modern tractors have roll over protection systems (ROPS) to prevent an operator from being crushed in the event of a rollover. This is especially important in open air tractors. In open air tractors the ROPS is a steel beam that extends above the operator's seat. For tractors with operator cabs, the ROPS is part of the frame of the cab. Before ROPS were required, many farmers were crushed to death when their tractors rolled over on top of them.
Most tractors have a means to transfer the engine's power to another machine such as a baler or reaper. Early tractors used belts wrapped around pulleys to power stationary equipment. Modern tractors use a power take-off (PTO) to provide rotary power to machinary that may be stationary or pulled. Almost all modern tractors can also provide hydraulic and electrical power.
Most equipment attached to the rear of the tractor use the three-point hitch (invented by Harry Ferguson) which has been a standard since the 1960s.
Engineering tractors
The durability and engine power of tractors made them very suitable for engineering tasks. Tractors can be attached with different engineering tools such as dozer blade, bucket, hoe, ripper etc. The most common attachments for the front of a tractor are dozer blade or a bucket. When attached with engineering tools the tractor is called engineering vehicle.
A bulldozer is a tracked-type tractor attached with blade in the front. Bulldozers are very powerful tractors and have excellent ground-hold, as their main tasks are to push or drag things.
Bulldozers have been further modified over time to evolve into new machines which are capable of working in ways that the original bulldozer can not. One example is that loader tractors were created by removing the blade and substituting a large volume bucket and hydraulic arms which can raise and lower the bucket, thus making it useful for scooping up earth and loading it into trucks.
A front-loader or loader is a tractor with an engineering tool which consists of two hydraulic powered arms on either side of the front engine compartment and a tilting implement. This is usually a wide open box called a bucket but other common attachments are a pallet fork and a bale grappler.
Other modifications to the original bulldozer include the reduction in size of the machine to permit it to operate in small work areas where movement is limited. There are also tiny wheeled loaders, officially called Skid-steer loaders but nicknamed "Bobcat" after the original manufacturer, which are particularly suited for small excavation projects in confined areas.
Backhoe loader
The most common variation of the classic farm tractor is the loader-backhoe, also called a backhoe-loader. As the name implies, it has a loader assembly on the front and a backhoe on the back. When both the loader and the backhoe are permenantly attached it is almost never called a tractor, not generally used for towing and usually does not have a PTO. When the backhoe is permenantly attached the machine ussually has a seat that can swivel to the rear to face the hoe controls. Removable backhoe attachments almost always have a separate seat on the attachment itself.
The backhoe-loaders are very common and can be used for a wide variety of tasks: construction, small demolitions, light transportation of building materials, powering building equipment, digging holes, breaking asphalt and paving roads. Some buckets have a retractable bottom, enable it to empty its load more quickly and efficiently. Retractable-bottom buckets are often also used for grading and scratching off sand. The front assembly may be a removable attachment or permanently mounted. Often the bucket can be replaced with other devices or tools.
Their relative small frame and percise control of the shovel/bucket and the backhoe made them very useful and common in urban engineering projects such as daily repairs and maintenance of the city. Their versatility and compact size makes them on of the most popular urban construction vehicles.
How a backhoe loader works (HowStuffWorks)
Other types of tractors
The term tractor is applied also to:
- road tractor
- heavy-duty vehicles with large engines and several axles. These tractors are designed to pull long road trailers, most often for the transport of freight of some kind over a significant distance (See Semi-trailer).
- locomotive tractor (engines)
- the amalgamation of machines , generators controls and devices that comprise the traction componant of railway vehicles
Tractors for aerospace and beyond
In aircraft, a tractor configuration refers to the propellers being in front of the fuselage or wing. Conversely if to the rear it is a called a pusher configuration.
NASA uses very large tractors to ferry launch vehicles like the Space Shuttle to (and in rare cases, from) the launchpad .
see Space Race
One might also ponderthe futuristic probability of the tractor beam and the cyberspace expansion to include file or packet tractors within the transport layer of the OSI Model. This falls into the field of internet:mechanics evolved conceptually from the tractor as a part of a printer that transports paper through the printer. (compare the adaptation of the term TTY still in use long after the Teletype machine faded into Cybernetic Antiquity.
See also
- List of farm implements
- Backhoe loader
- Bulldozer
- Crane
- Engineering vehicles
- Excavator
- Grader
- Front loader
- Skid loader