1st Edition

Optimizing Small Multi-Rotor Unmanned Aircraft A Practical Design Guide

By Stephen Prior Copyright 2019

    This design guide was written to capture the author’s practical experience of designing, building and testing multi-rotor drone systems over the past decade. The lack of one single source of useful information meant that the past 10 years has been a steep learning curve, a lot of self-tuition and many trial and error tests. Lessons learnt the hard way are not always the best way to learn. This book will be useful for the amateur drone pilot who wants to build their own system from first principles, as well as the academic researcher investigating novel design concepts and future drone applications.


    2 Lithium Polymer battery (power supply)
    2.1 Safety considerations
    2.2 Lithium Polymer discharge characteristics

    3 Electronic Speed Controller (ESC)
    3.1 Timing
    3.2 Cut-off voltage
    3.3 Switching frequency

    4 The Brushless DC (BLDC) motor (outrunner)
    4.1 BLDC motor construction and theory
    4.2 Equivalent brushed DC motor equations
    4.3 Comparing theoretical and empirical data

    5 The propeller (rotor)
    5.1 Propeller or rotor?
    5.2 Propeller variables
    5.3 Propeller geometry
    5.4 Simple momentum theory
    5.5 Non-dimensional rotor (propeller) coefficients
    5.6 Figure of Merit (FM)
    5.7 Propeller efficiency (p)
    5.8 Co-axial and overlapping rotor designs
    5.9 Reynolds number, Re
    5.10 Airfoil geometry
    5.11 Airfoil theory – Blade Element Theory (BET)
    5.12 Online airfoil resources

    6 The system solution
    6.1 IMechE UAS challenge – a worked multi-rotor example
    6.2 Measuring the propulsive efficiency
    6.3 Forward flight
    6.4 Dihedral and cant angles
    6.5 Active thrust vectoring

    7 Conclusion
    7.1 Economic and societal impact
    7.2 Future directions, opportunities and threats

    Appendix A1 Li-Po batteries ready reckoner (6S)
    Appendix A2 A range of 6S Li-Po batteries with high specific energy (Wh/kg) (June 2018)
    Appendix B Guidance on the safe use, handling, storage and disposal of Lithium Polymer batteries
    Appendix C T-Motor BLDC motor selection tool
    Appendix D Overall system selection spreadsheet
    Appendix E Examples of multi-rotor systems built at the ASL
    Appendix F Drone radio frequency legal requirements in the UK
    Appendix G Example Pixhawk flight controller wiring diagram and mission planner set-up (PID tuning)


    Dr Stephen D Prior is Reader in Unmanned Air Vehicles within the Faculty of Engineering and the Environment at the University of Southampton. He gained a BEng in Mechanical Engineering degree in 1987 and PhD in Robotics from Middlesex University, London in 1993. He is a Chartered Mechanical Engineer, Corporate Member of the IMechE and Fellow of the Higher Education Academy. His research interests are in the areas of Mechatronics, Autonomous Unmanned Systems, Robotics and Design Engineering. He was Project Lead for the MoD Grand Challenge i-Spy team in 2008 and was the Team Leader for Team HALO, winner of the DARPA UAVForge Competition 2012. He has been an editor for the International Journal of Micro Air Vehicles since 2010.