A quadcopter, or multirotor, drone, or quadrotor, is a simple flying mechanical vehicle that has four arms, and in each arm there is a motor attached to a propeller. Multicopters with three, six or eight arms are also possible, but work on the same principal as a quadcopter. Two of the rotors turn clockwise, while the other two turn counter clockwise. Quadcopters are aerodynamically unstable, and require a flight computer to convert your input commands into commands that change the RPMs of the propellers to produce the desired motion.
Quadcopters today, are very easy to fly in any direction. They can also hover in place super smoothly. The engineering and design is different to an airplane or helicopter for flying.
Quadcopters differ from a helicopter or a fixed wing aircraft in the way they generate lift and control forces. For an aircraft the lift is generated by the wings, but in a quadcopter the lift is generated by the propellers. A helicopter uses its main rotor to generate lift, but also have the ability to vary the pitch of the rotor blades to generate control forces.
The quadcopter concept is not new. Manned quadcopter designs appeared in the 1920s and 1930s, but these early concepts had bad performance, a high level of instability, and required a lot of pilot inputs. The advancement of electronic technology in flight control computers, coreless or brushless motors, smaller microprocessors, batteries, accelerometers, cameras, and even GPS systems made it possible to design and fly quadcopters. The simplicity of the quadcopter has made it a very effective aerial photography and video platform.
In the last few decades, the quadcopter layout has become popular for small-scale unmanned aerial vehicles or drones. The need for aircraft with greater maneuverability and hovering ability has led to a rise in quadcopter research. The four-rotor design allows quadcopters to be relatively simple in design yet highly reliable and maneuverable.
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.
Due to their ease of construction and control, quadcopters are popular as amateur model aircraft projects.