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Lawnmower)
A lawn mower (often spelled as one word—lawnmower) is a machine (electric or mechnanical) used to cut grass to an even length. It was invented in Britain in 1830 by Edwin Beard Budding, primarily to cut the lawn on sports grounds and expansive gardens. Since many sports had just been invented in Britain that required a flat soft ground (such as croquet, cricket, soccer and rugby), a more efficient way of making uniform length grass was needed, and so the lawn mower was born.
Previously, grass was cut by hand using a scythe and before that, by a sickle.
Electric rotary lawn mower with rear catcher, side view
There are two main types of lawnmowers—
- those where a set of spiral-cylindrical blades spin on a horizontal axis (reel mower)
- those whose blades spin horizontally on a vertical drive-shaft (rotary mower)
The former is the design from 1830 and they were manually powered. Nowadays most are powered. The latter type is powered by two-stroke or four-stroke internal combustion engines running on petrol or other liquid fuels, although versions with electric motors are becoming increasingly popular. Cordless electric lawnmowers are also available for small lawns.
The simplest kind of mower is the manual push (reel) mower. These always use the cylindrical type blades (the reel). It works by spinning the cutting blade at speed with power supplied by the user pushing it and rotating its wheels that are geared to the cutting reel. The mower moves forward and the blades rotate over the grass, pulling it into the reel and against a horizontal plate just above ground level—the blade and plate come together in a scissor-like slicing action that cuts the grass.
Power mowers
Lawnmower engines usually have only one cylinder. Power ranges from 2 to 6 horsepower (1.5 to 4.5 kW). The engines are usually carburated and require a manual pull to start them, although electric start may be used too.
The simplest type of power mower is basically a push mower with an engine—the engine rotates the cutters and drives the machine forward. In the last twenty or thirty years it is also common to find this type of mower with an electric motor as the power source, though this has the disadvantage of requiring a trailing power cord that limits its range, so these are only useful for relatively small lawns close to a power socket. There is also the obvious hazard with these machines of the possibility of mowing over the power cable.
Underneath electric mower, showing mulching blade
Rotary mowers
An alternative mechanism for cutting grass is a horizontally spinning blade held close above the grass surface. This type is usually referred to as a rotary mower. One of the first companies to exploit this principle commercially was the Australian Victa company, in 1947. These mowers are always powered, using either an internal combustion engine or an electric motor. Usually, these mowers are moved by manual motive power—the onboard engine or motor only spins the blades. The most common type is fitted with wheels, but an alternative is the hover mower, in which the spinning blade also acts as a fan providing a lift force, lifting the mower bodily clear of the ground on the same principle as a hovercraft. Such mowers are very light and easy to manoeuvre, provided the grass surface is fairly even. Rotary mowers typically have an opening in the side of the housing where the cut grass is expelled. Some have a grass catcher attachment at that point to bag the grass clippings. Rear-catchers is another common design for the same purpose.
Special "mulching" blades are now also available for rotary mowers. The blade is designed to keep the clippings circulating underneath the mower until the clippings are chopped quite small. Other designs have twin blades to mulch the clippings to small pieces. This avoids the need for bagging the clippings or raking the clippings. Not only does this save labour, as no organics are removed from the lawn, less fertilizer is needed.
On rotary mowers, the blade is seldom sharp enough to cut the grass blades. The speed of the blade simply tears the grass resulting in brown tips. By contrast, the cylinder-type lawnmowers and manual lawnmowers usually work by scissor action on the blades and a cleaner cut is achieved.
Different grass lengths may be desirable at different times of the year or in different parts of the lawn. The height of the lawnmower can usually be adjusted to control the height of the cut grass. On older or less expensive lawnmowers, this is accomplished by manually moving each wheel to a different slot on the chassis. A more recent innovation is a "one-touch" height-adjust mechanism where the wheels are mounted on a frame separate from the rest of the lawnmower and the frame can be raised and lowered. In general, vertical mowers can cut closer to the ground than horizontal mowers.
In some countries modern power mowers may have a "deadman's switch" which requires the operator to hold a switch to keep the engine running. Typically, this is an extra bar that is held against the handle. Should the operator drop "dead" or otherwise lose control of the lawnmower and release the bar, either the engine is turned off or the blade is disconnected by disengaging a clutch. The switch may be mandated by local legislation.
Self-propelled mowers
All mowers which require a human to push or manoeuvre them become quite tiring once the area of grass to be cut becomes more than a few tens of square metres. There are self-propelled mowers in which the wheels are powered but the operator is still required to walk behind the mower to steer it. These are only slightly more expensive than regular push mowers. A popular alternative for larger domestic properties is the ride-on mower. These often resemble small tractors, with the cutting deck mounted amidships between the front and rear axles. Such machines are convenient for large lawns. An alternative layout for a ride-on is a rear-mounted engine with rear-wheel steering, and a front-mounted deck. These mowers are generally more manoeuverable around tight corners than the tractor type, but are generally more expensive. Most of these machines cut using the horizontal rotating blade system, though usually with multiple blades.
Professional mowers
Professional grass-cutting equipment (used by large establishments such as universities or local authorities, etc), usually take the form of much larger dedicated ride-on platforms, or attachments that can be mounted on a standard tractor unit. Either type may use rotating blades or the cylindrical blade type cutters.
Other mowing aids
Edge trimmer
Edge trimmers (also called line trimmers or wipper-snippers in Australia) are specialized, electric or petrol-engine powered, hand-held mowers for cutting grass near fences, trees and other areas too small or rough for a mechanized lawnmower. The cutting device is either a monofiliment nylon 1.6 to 3 mm diameter line, or a nylon or steel three-lobe blade.
Electric wipper-snippers have the advantage of being very light, easy to manouvre and easy to operate devices. However, they are limited by the length of power cord that can be deployed across the ground and they are usually less powerful and robust than the petrol-engined ones. Electric machines normally are limited to 2.5 mm (0.100 inch) maximum diameter nylon because of their lower power output (400 to about 1200 watts).
Petrol-engine powered trimmers usually have a minimum of 25 cc motors. At this size they can easily turn 2 mm (0.080 inch) line and some have nylon blades as accessories to the line-reel. A 32 cc engine can swing a 2.75 mm (0.110) line and often have metal-blade accessories.
While this type of trimmer is heavier, uses petrol-oil mix and vibrates significantly they are much more mobile (not attached to a power outlet) and are not very limited in maximum power for commercial use. Large trimmers, used for cutting roadside grass in large areas, may be quite heavy—being suspended from the body by a harness— and be a two-hand-controlled device.
For trimming close to fences and other snagging features, petrol-trimmers can be throttled back to limit the chance of the line catching or breaking off, or both. Speed-control is not possible with electric trimmers—they are essentially single-speed machines.
A line-trimmer works on the principle that a line that is turned fast enough is held out from its housing (the rotating reel) very stiffly by centrifugal force. The faster it turns the stiffer the line. Even round-section nylon line is able to cut grass and slight, woody, plants quite well. Some monofilament, designed for more powerful cutters, has an extruded shape—like a star—that helps the line slash the material being cut and it is able to cut quite large woody plants (small shrubs) or, at least, ring-bark them very effectively. These lines make disks less necessary for tough jobs.
The line is hand-wound onto a reel before the job is started—leaving both ends extending from the reel-housing. The reel is turned by the motor and the line extends horizontally while the operator swings the trimmer about where the plants are to be trimmed. The operator controls the height that cutting takes place and can trim down to ground level quite easily. As the line is worn, or breaks off, the operator knocks the reel on the ground so that a release mechanism allows some of the line in the reel to extend and replace the spent portion. A small cutter on the line-guard ensures that the line length exposed for cutting does no exceed the length that can be swung efficiently by the motor. Newly extended line operates more efficiently because of its heavier weight and surface effects (the star-shaped edges).
Trimmers that have nylon or metal blades usually have straight driveshafts because of the higher torque required to turn the disk and because of the shock loads that are passed back from the blade to the driveshaft and its gearbox(es). Smaller line trimmers have curved driveshafts to make holding the cutting-head at ground level much easier and less strain on the operator.
Safety precautions, often ignored, with wipper-snippers are that the operator should wear robust boots and clothing (especially trousers), goggles, hearing protection and gloves. The power should be disconnected (or the engine stopped) before the line is replaced or before any significant work is done in the line-reel area (such as removing grass stalks that have wound onto the reel). The line guard should not be removed because it stops material being flung back at the operator's legs and because it carries the cutter ensuring that the line length is not too long for the trimmer. When using a disk the operator can easily overload the driveshaft and damage the machine or strip the gearbox gears.
Clippers
Hand-powered or battery-electric grass clippers can used for the tightest spots, however one has to be on their knees a lot.
Robotic mowers
Robotic lawnmowers represented the second largest category of household robots used by the end of 2003, with 37,000 units sold [1]. One of the manufacturers is Friendly Robotics with its RoboMower product. A robotic lawnmower requires the user to set-up a border wire around the lawn that defines the area to be mowed. Afterwards it can operate completely autonomously, recharging as necessary. The company also sells a robotic vacuum cleaner.
See also
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