For motor-just applications, the slower the electric motor speed, the bigger the motor must be. Large motors can be expensive and may not fit within the allowable envelope space of a credit card applicatoin. Utilizing a gearbox with a smaller sized motor allows the unit to use at lower speeds.
To be able to understand the need for using a gearbox to decrease motor speed, consider this situation. You have a pastry speed gearbox conveyor that adds cherry filling as the pastries pass. Because this is a fairly light load, you’ll not want the conveyor working at 5000 rpm. If it was, there would be pastries and cherry filling all over the place!