Why is it that chainsaws need a pull cord to start? Couldn’t they just be turned off or on with a switch?
In: Engineering
An engine that runs on gas or gas/oil mixture is generally one that explodes that fuel to drive one or more pistons, etc. You can’t start such an engine just by applying electricity to it, you have to get process of firing the spark plug to turn the crank started. If you fired a spark plug when the piston mechanism was in the wrong position, the piston would drive the engine in the wrong direction.
So the way to get such an engine started is to move the whole mechanism a little bit in the proper direction while electricity is available for the spark to fire at the correct time. Really old cars had a crank; manual transmission cars can still be started by turning on the ignition, pushing the car forward at a mile or two per hour with the clutch pedal pushed in, and then releasing the clutch suddenly (to move the pistons, etc.).
In order to start with a switch, the chainsaw would need some equivalent to an automobile’s starter motor: something that would take stored electricity (like a car battery) and jerk the motor forward. Such a mechanism would increase the weight, cost, and complexity of the chainsaw mechanism, so they don’t normally do it. Chainsaws have to be small and light enough that they can be manipulated while working, so increasing weight is likely the biggest factor.
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