In present days, autonomous multi-rotor copters are increasingly becoming popular due to its advantages in terms of multi-purpose functionalities, robustness, high dynamic response and more significantly inexpensive costs of development and usage. However, real-time attitude estimation is a key component which needs to have further development for better control and precise navigation to drive these unmanned aerial vehicles reliably. This paper presented an approach to improve the method of attitude estimation by Direction Cosine Matrix for multi-rotor copters that is based on low cost MEMS inertial sensors, a magnetometer and a commercial GPS receiver. In connection with the Direction Cosine Matrix attitude estimation scheme, a novel algorithm design for dealing with limitations on attitude sensing accuracy and reducing latency in real-time is proposed. The design is insensitive to noise or loss of GPS signals. The viability of the proposed design is demonstrated by an experimental scenario with real-time attitude information under different observations. From the experiment, some issues have been noticed and their reasons have been discussed.