As the question currently appears (What motor is used on grass cutter machines?), this is a very wide scope.
The size of machine will range from the smallest string-trimmers (400 Watts / 1/2 HP) to the largest hay-harvesting combines, called reapers and reaper-binders, which can be powered by diesel engines of up to 405kW / 543 HP.
A “typical” domestic, powered grass cutter, called a lawnmower, is usually hand-propelled and will have a petrol/gasoline engine of between 2.2 kW to 3.7 kW (3 HP to 5 HP). The smaller machines will often be fitted with a 2-stroke engine while the larger ones are generally fitted with a 4-stroke engine. They will normally be fitted with a manual starting system operated with a pull-chord. Machines larger than these are also available with diesel engines.
Where an electricity supply is practical, domestic lawnmowers are available with electric motors which range between 1 kW to 2.5 kW / 1.3 HP to 3.4 HP. These motors are almost always constant-speed induction (“squirrel-cage”) motors. Many people who are reluctant to maintain internal-combustion engines prefer the simplicity of the electrical alternative.
Small, hand-held, grass trimmers (“string-trimmers”/“weed whackers”/”brush cutters”) can be powered with small 2-stroke engines of 20 cc and bigger - or compound (“universal”, i.e. AC/DC) motors of 500 W and bigger.
Any grass-cutting machine larger than a domestic lawnmower will be powered by an internal combustion engine and those rated over 7.5 kW / 10 HP will almost always have power-driven wheels as well, since such a large machine becomes impractical to propel by hand. Such large machines may be fitted with an electric starter, requiring a battery to be installed on the machine. There are also mechanical spring-powered starters which are tensioned through reduction gearing, allowing the operator to “wind up” the spring with a large number of undemanding turns of a crank-handle. A mechanical push-button system then allows the wound-up spring to turn the engine for starting. A properly-tuned engine fitted with such a starter will start up quickly enough to allow multiple starts from one full winding.