Tricopter is an aircraft similar to a helicopter and quadcopter except it has three motors. The yaw is controlled by the servo turning the back motor. The beauty of the design compare to quadcopter is that 1) foldable; 2) natural flying orientation; 3) fewer point of failure. It is simple, cheap, easy to build with no advanced electronics needed. Oscar Liang explains how he made his own large tricopter after making several smaller quad ones.