A quadcopter is a multicopter lifted and propelled by four rotors. The motors are mounted in the same plane, on the helicopter, forming a square. This allows this quadcopter to lift vertically without rotating on itself. There are several advantages to quadcopters over comparably-scaled helicopters. The fact that four motors are involved reduces the minimum size of the propellers on each motor. This means that in case the quadcopter hits anything the damage is significant less than if a similar sized helicopter crashed. The following figure shows how the motors are mounted. The rotation direction is critical to the correct functioning of a quadcopter.
All motors have to rotate at the same speed for a vertical lift; however, motor 1 and 3 have to rotate opposite to motors 2 and 4. This is necessary to compensate the angular acceleration generated by each motor. This way the total angular acceleration should be zero, maintaining the quadcopter �stable�.
According to Wikipedia, flight dynamics is the science of air vehicle orientation and control in three dimensions. Roll, pitch and yaw as shown in the picture below are the three critical flight dynamics parameters, which are the angles of rotation in three dimensions about the flying object’s center of mass. In our project, we use our IMU chip to measure these values and also employ the PID (proportional�integral�derivative controller) system from lab 4 to fine-tune them. Roll, pitch, yaw and throttle (up and down) movements are controlled by an Xbox joystick.