While quadcopters have become very popular in recent years, there are still some inherent limitations in the design that includes multiple motors and multiple propellers. For one thing, there is a theoretical limit in the size you could go with multiple propellers given the need for more motors. The quadcopter design was rejected years ago by the United States military for the simplicity of a single rotor. However, today with better flight controllers and electronics to control the aircraft, the quadcopter design is taking off.
To learn more about the advantages and disadvantages of the quadcopter versus helicopter design, click here.