Skid-steer loader

A Gehl skid loader

A skid loader or skid-steer loader is a small rigid frame, engine-powered machine with lift arms used to attach a wide variety of labor-saving tools or attachments. Though sometimes they are equipped with tracks, skid-steer loaders are typically four-wheel vehicles with the wheels mechanically locked in synchronization on each side, and the left-side drive wheels can be driven independently of the right-side drive wheels.

The wheels typically have no separate steering mechanism and hold a fixed straight alignment on the body of the machine. By turning the left and right wheel pairs at different speeds, the machine turns by skidding, or dragging its fixed-orientation wheels across the ground. The extremely rigid frame and strong wheel bearings prevent the torsional forces caused by this dragging motion from damaging the machine.

The skid-steering vehicle is turned by generating differential velocity at the opposite sides of the vehicle. Like tracked vehicles, the high ground friction produced by skid steers can rip up soft or fragile road surfaces. They can be converted to low ground friction by using specially designed wheels such as the Mecanum wheel.

Skid-steer loaders are capable of zero-radius, "pirouette" turning, which makes them extremely maneuverable and valuable for applications that require a compact, agile loader.

Unlike in a conventional front loader, the lift arms in these machines are alongside the driver with the pivot points behind the driver's shoulders. Because of the operator's proximity to moving booms, early skid loaders were not as safe as conventional front loaders, particularly during entry and exit of the operator. Modern skid loaders have fully enclosed cabs and other features to protect the operator. Like other front loaders, it can push material from one location to another, carry material in its bucket or load material into a truck or trailer.

History

A John Deere 280 skid loader moving mulch

The first three-wheeled, front-end loader was invented by brothers Cyril and Louis Keller (manufacturer) in Rothsay, Minnesota, in 1957. The Kellers built the loader to help a farmer mechanize the process of cleaning turkey manure from his barn. The light and compact machine, with its rear caster wheel, was able to turn around within its own length, while performing the same tasks as a conventional front-end loader.

The Melroe brothers, of Melroe Manufacturing Company in Gwinner, N.D., purchased the rights to the Keller loader in 1958 and hired the Kellers to continue refining their invention. As a result of this partnership, the M-200 Melroe self-propelled loader was introduced at the end of 1958. It featured two independent front-drive wheels and a rear caster wheel, a 12.9-hp engine and a 750-lb. lift capacity. Two years later they replaced the caster wheel with a rear axle and introduced the M-400, the first four-wheel, true skid-steer loader. It quickly became the Melroe Bobcat. The term "Bobcat" is sometimes used as a generic term for skid-steer loaders; however, such uses are inaccurate because "Bobcat" is a brand of equipment. The M-440 was powered by a 15.5-hp engine and had an 1100-lb. rated operating capacity. Skid-steer development continued into the mid-1960s with the M600 loader.

Many manufacturers have their own versions of the skidloader (often referred to as a Skidsteer in the Construction Industry), including: LiuGong, Volvo, John Deere, Case, JLG, JCB, New Holland, Gehl Company, Mustang, ASV, Caterpillar, Bobcat, Komatsu, Hyundai, and more.

Attachments

Bobcat skid loader clearing snow with snowblower attachment

A skid steer with a power-driven auger attachment

Trencher attachment

The conventional bucket of many skid loaders can be replaced with a variety of specialized buckets or attachments, many powered by the loader's hydraulic system. These include backhoe, hydraulic breaker, pallet forks, angle broom, sweeper, auger, mower, snow blower, stump grinder, tree spade, trencher, dumping hopper, ripper, tillers, grapple, tilt, roller, snow blade, wheel saw, cement mixer, and wood chipper machine.

Some models of skid steer now also have an automatic attachment changer mechanism. This allows a driver to change between a variety of terrain handling, shaping, and leveling tools without having to leave the machine, by using a hydraulic control mechanism to latch onto the attachments. Hydraulic supply lines to powered attachments may be routed so that the couplings are located near the cab, and the driver does not need to leave the machine to connect or disconnect those supply lines.

Loader-arm design

Skid steer using a multi-hinge parallel bar bucket lift mechanism, for greater lift height and a more vertically oriented bucket lift path, while retaining a compact device size

The original skid-steer loader arms were designed using a hinge at the rear of the machine to pivot the loader arm up into the air in an arc that swings up over the top of the operator. This design tends to limit the usable height to how long the loader arm is and the height of that pivot point. In the raised position the front of the loader arm moves towards the rear of the machine, requiring the operator to move extremely close to or press up against the side of a tall container or other transport vehicle to get the bucket close enough to dump accurately. At the highest arm positions, dumping the bucket may dump directly onto the top of the machine's cab.

An extended reach design uses multiple hinges and parallel lifting bars on the loader arm, with the main pivot points towards the center or front of the machine. This allows the loader arm to have much greater operating height while retaining a compact design, and allows the vertical movement to be less of an arc and more straight-up vertical, to keep the bucket forward of the operator's cab, allowing safe dumping into tall containers or vehicles.

Applications

A skid-steer loader can sometimes be used in place of a large excavator by digging a hole from the inside. The skid loader first digs a ramp leading to the edge of the desired excavation. It then uses the ramp to carry material out of the hole. The skid loader reshapes the ramp making it steeper and longer as the excavation deepens. This method is particularly useful for digging under a structure where overhead clearance does not allow for the boom of a large excavator, such as digging a basement under an existing house.

See also

• Compact excavator
• Backhoe loader
• Bulldozer
• Crane
• Excavator
• Forklift
• Grader
• Front loader
• Amphibious vehicle
• Skid-to-turn
• Tractor

External links

Media related to Skid-steer loaders at Wikimedia Commons

• "HOW THE BOBCAT SKID-STEER LOADER CAME TO BE, by Joe Keller
• How Skid Steer Loaders and Multi Terrain Loaders work - from HowStuffWorks.com
• U.S. National Institute for Occupational Safety and Health Alert: Preventing Injuries and Deaths from Skid Steer Loaders. February 1998.
• Skid Steer Loader Safety, Kansas State University
• "8th-grade grads invented, Ph.D.s explained their inspirations," by Edward Lotterman, St. Paul Pioneer Press, July 15, 2010