Electronics and Vision System of a Projectile-Drone Hybrid System These control signals are generated by a controller from Robbe. The engine rotation speed is based on a PWM signal input from the controller. The relationship between the PWM signal and the engine rotation speed is unfortunately not known; it is not linear, and the control is open loop; thus, a control board was developed to achieve the closed loop motor speed control. The rotation speed is extracted by an analog filter and it is communicated to a microcontroller. A proportional-integral-derivative control implemented on the microcontroller will update the PWM signal sent to the controller to follow a speed reference. ACCURACY ENHANCEMENT OF THE IMU The GLMAV needs to know exactly its angles of roll, pitch, and yaw, as well as its speed and position, to ensure autonomous navigation. The attitude angle measurements must be better than 1° to achieve a good positioning of the counter-rotating helicopter. The vehicle must embark an inertial measurement unit (IMU) to carry out these measurements. The IMU must be compatible with many mechani- Figure 8. Estimation of the altitude by Kalman filter. Figure 9. Screenshot of the graphic interface running on the ground station computer. 44 IEEE A&E SYSTEMS MAGAZINE OCTOBER 2017