Physics; heterogeneous multirotor; cascaded PID control; automatic tuning; stable reference tracking; stable flight operation; Proportional integral derivative; Frequency response; Robust control; Control systems; Energy efficiency; Frequency dependence; Rotary wing aircraft; Configurations; COVID-19; Maneuverability; Attitude control; Control algorithms; Helicopters; Control systems design; Flight control systems; Unmanned aerial vehicles; Experiments; Endurance; Controllers; Rotors; Design; Tuning; Helicopter control; Reynolds number; Relay feedback