A Quadcopter is an unmanned aerial vehicle (UAV) or drone with four rotors, each with a motor and propeller. 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.
I was amazed by this technology a had started building a quadcopter. Equipped with cheap components from HobbyKing, the copter flew, but was almost uncontrollable, crashing into the ground often.
The next version of the quadcopter re-used almost all component, like the flight-controller and motors but was built with a more robust hollow metal frame.
Our quadcopters evolved very similarly to the tricopters. We used several frame-types and the flight controllers evolved from ArduCopter to OpenPilot to DJI-Naza.
After the suboptimal results with a smaller quad, I started building bigger, much bigger quad and hexa-copters that could carry small cameras.
Hexacopter dubbed DragonFly had an all-up weight of 2869 gr.