Introduction

The term “drone” usually refers to any unpiloted aircraft also known as UAVs (Unmanned Aerial Vehicles / Uncrewed Aerial Vehicle) while a quadcopter comes from two words which is "Quad " that means four and "Copter" is another term for helicopter. I know that the quadcopter is new to you guys coz you've probably only heard of the term "Drones", "UAVs","Helicopter" and an "Aircraft". So let me explain more on the Quadcopters.

[ Quadcopters]

A quadcopter or quadrotor refers to the type of helicopters with four rotors (rotary blades). The small size and low inertia of drones allows use of a particularly simple flight control system, which has greatly increased the practicality of the small quadrotor in this application. Quadcopters generally have two rotors spinning clockwise (CW) and two counterclockwise (CCW). Flight control is provided by independent variation of the speed and hence lift and torque of each rotor. Pitch and roll are controlled by varying the net centre of thrust, with yaw controlled by varying the net torque.

Unlike conventional helicopters, quadcopters do not usually have cyclic pitch control, in which the angle of the blades varies dynamically as they turn around the rotor hub. In the early days of flight, quadcopters were seen as a possible solution to some of the persistent problems in vertical flight. Torque-induced control issues can be eliminated by counter-rotation, and the relatively short blades are much easier to construct.

[Drones]

Around 2005 to 2010, advances in electronics allowed the production of cheap lightweight flight controllers, accelerometers (IMU), global positioning system and cameras. This resulted in the quadcopter configuration becoming popular for small unmanned aerial vehicles. With their small size and maneuverability, these quadcopters can be flown indoors as well as outdoors. For small drones, quadcopters are cheaper and more durable than conventional helicopters due to their mechanical simplicity. Their smaller blades are also advantageous because they possess less kinetic energy, reducing their ability to cause damage. For small-scale quadcopters, this makes the vehicles safer for close interaction. It is also possible to fit quadcopters with guards that enclose the rotors, further reducing the potential for damage. However, as size increases, fixed propeller quadcopters develop disadvantages relative to conventional helicopters. Increasing blade size increases their momentum. This means that changes in blade speed take longer, which negatively impacts control. Helicopters do not experience this problem as increasing the size of the rotor disk does not significantly impact the ability to control blade pitch. Due to their ease of construction and control, quadcopters are popular as amateur model aircraft projects.

More information can be access here and here (UAVs & RPA)