**2.2.2 Navigation system**

In the design of the navigation system, we followed some principles. First, the system must be compact and easy to equip on the airframe. Second, the system should use low-cost sensor to reduce the RUAV system's cost. Third, the system should be designed as light as possible to save fuel and increase the payload. Precision navigation information of flight state is needed to realize the autonomous control of the RUAV. Generally, navigation information must include positions, velocities, accelerations, attitude, heading and angular velocities in 3-axis. The architecture of the navigation system is shown in Figure 4 (Wu, et al., 2010).

Fig. 4. Hardware Architecture of Navigation System

We use GPS receiver to give position and velocity. But the altitude given by GPS generally has a fluctuation of 5m, and it is not accurate enough to control the RUAV. So a barometer is needed to give a more accurate measurement of the relative altitude. Even though the barometer is more accurate in relative altitude, it is susceptible to weather condition and may vary significantly in different weather. Because the altitude given by GPS is much more unsusceptible to weather, a combination of GPS altitude and barometer altitude will give more accurate and stable altitude information.

Attitudes' accuracy is the key point for the stability of the RUAV since the position control of the RUAV is coupled with the attitude. We use IMU to measure the acceleration and angle velocity. By referring to a low-cost attitude design described in literature (Gao et al., 2006), we determine the attitude in pitch and roll by accelerometers and gyroscopes. A simple calculation of acceleration may be suitable for the RUAV in hovering and other mode with low maneuverability in low acceleration, but in high maneuverability mode with high acceleration, the measurement will deviate a great deal because the measurement of accelerometers include not only gravity acceleration but also absolute acceleration. So a feedback from velocity is added to decrease the influence of absolute acceleration.

The yaw of RUAV will be calculated by the magnetic field measured by the magnetometer. Due to the deviation of magnetic field of the earth in different places, a revision of magnetic field would be necessary to get the real yaw.

Compared with previous generation, this navigation system uses independent processor. We choose LPC3250 as the calculation and acquisition processor. A two-stage EKF is implemented to estimate the flight state. Further research in navigation theory can be conducted by using this system.

Fig. 5. The navigation system

618 Advances in Wavelet Theory and Their Applications in Engineering, Physics and Technology

2150 mm. The total height of the helicopter is 770mm, the full width of it is 720mm, and the total length is 2680mm. The maximum airspeed is 100 km/h, and it can cruise 1 hour at

In the design of the navigation system, we followed some principles. First, the system must be compact and easy to equip on the airframe. Second, the system should use low-cost sensor to reduce the RUAV system's cost. Third, the system should be designed as light as possible to save fuel and increase the payload. Precision navigation information of flight state is needed to realize the autonomous control of the RUAV. Generally, navigation information must include positions, velocities, accelerations, attitude, heading and angular velocities in 3-axis. The architecture of the navigation system is shown in Figure 4 (Wu, et

GPS Receiver

Microprocessor

Accelerometer

Magnetometer

Fig. 4. Hardware Architecture of Navigation System

more accurate and stable altitude information.

field would be necessary to get the real yaw.

Barometer

Gyroscope

We use GPS receiver to give position and velocity. But the altitude given by GPS generally has a fluctuation of 5m, and it is not accurate enough to control the RUAV. So a barometer is needed to give a more accurate measurement of the relative altitude. Even though the barometer is more accurate in relative altitude, it is susceptible to weather condition and may vary significantly in different weather. Because the altitude given by GPS is much more unsusceptible to weather, a combination of GPS altitude and barometer altitude will give

Attitudes' accuracy is the key point for the stability of the RUAV since the position control of the RUAV is coupled with the attitude. We use IMU to measure the acceleration and angle velocity. By referring to a low-cost attitude design described in literature (Gao et al., 2006), we determine the attitude in pitch and roll by accelerometers and gyroscopes. A simple calculation of acceleration may be suitable for the RUAV in hovering and other mode with low maneuverability in low acceleration, but in high maneuverability mode with high acceleration, the measurement will deviate a great deal because the measurement of accelerometers include not only gravity acceleration but also absolute acceleration. So a

The yaw of RUAV will be calculated by the magnetic field measured by the magnetometer. Due to the deviation of magnetic field of the earth in different places, a revision of magnetic

feedback from velocity is added to decrease the influence of absolute acceleration.

Flight Control System

Navigation Information Output

36 km/h speed.

al., 2010).

**2.2.2 Navigation system** 

The IMU, GPS, barometer, magnetometer and processor are integrated in a compact circuit, as shown in Figure 5. The primary parameters of compacted navigation system are shown in Table2.


Table 2. Sensors Parameters
