This paper describes development and validation processes of a low-cost hardware based flight control computer designed for multi-rotor UAVs. The developed flight control computer controls multi-rotors stable and can handle complex flight missions using an integrated high-performance Linux computer. A complementary filter generates a navigation solution with 500 Hz, and a proposed observer significantly reduces measurement noise. A control algorithm utilizes a feed-forward term computed by a three-dimensional curve fitting method, and it increases tracking performance. The developed flight control system has been fully tested through several test flights, and it can apply to real flight environments.