Industrial vs domestic
There are mainly two types of sewing machines are available. They are industrial and domestic. Industrial sewing machines are larger, faster, and more varied in their size, cost, appearance, and task. An industrial sewing machine can handle heavy-duty sewing jobs. Industrial machines, unlike domestic machines, perform a single dedicated task and are capable of continuous use for long periods; they have larger moving parts and larger motors rated for continuous operation. Parts for different industrial machines, such as motors, sewing feet, and bobbins may be interchangeable, but this is not always so.
The motors on industrial machines, as with most of their components, lights, etc., are separate, usually mounted to the underside of the table. Domestic machines have their OEM motors mounted inside the machine. There are two different types of motor available for industrial machines: a servo motor (which uses less electricity and is silent when not in use), and the more traditional clutch motor (which is always spinning; even when not in use).
A clutch motor is always running and making noises when it is connected to electricity. The constant operation ensures consistency and speed.
The servo motor uses less electricity than a clutch motor. It does not make any sound unless the operator hits the pedal on the machine, but it cannot withstand the same kind of use as a clutch motor.