PWM signal generation for a quad-rotor with variable geometry arms

Abstract

This paper presents a methodology to transform two PWM signals into four is presented to generate the motion of the arms of a quadcopter having a variable frame geometry. Each arm can rotate around each axis by arms’ actuators. The four angles describing the angular position of the arms have been introduced. Based on the different geometric configurations of arms, the pitch and roll rotation of the quadcopter is developed. The algorithm that characterizes the control’s logic is based on few assumptions derived from the structure of the joystick’s motion and the maximum PWM width that each servo can develop corresponding to the maximum rotation of the arm. A specific geometric constraint is introduced so that all possible values of two combined PWM signals can be transformed that do not violate the maximum amount of PWM signal directed to the servo. The experimental validation is built up by using a commercial hardware characterized by four servos, a rotary encoder, one control board and an oscilloscope to validate the generated signal developed by the mathematical algorithm installed on the control board.