1 Fabrication and optimisation of an electrical motorisation for mini-UAV in hovering Nicolas Achotte, Jérôme Meunier-Carus, G. Poulin, J. Delamare, O. Cugat Laboratoire d’Electrotechnique de Grenoble - France

2 Electric propulsion chain for hovering Global/elementary optimisation Traction Output power Rotation speed Figure of Merit Hovering Dimensions Mass Autonomy Noise Payload Specification sheet Optimisation tool necessary ! Voltage Current Efficiency Capacity (A.h)

3 Electrical motorisation for mini-UAV Experimental study –Hovering power evaluation –Test bench –Experimental results and characterisations –Realisation of global traction chain Design of an planar miniature magnetic motor –Modelling –Structure choice & dimensioning Optimisation of the entire chain Perspectives - Conclusion

4 Power needed to hover a given mass Theory : Momentum theory (Rankine, 1865; Froude, 1885; Betz, 1920) Figure of merit : ~ hovering ‘’ efficiency ‘’ Mechanical power for hovering :

5 Test bench Propeller Motor Speed sensor Thrust sensor Torque sensor Speed controller Fully automated laptop Batteries Ball bearings

6 Tests on propellers Dimensions (50 cm) and non compressible fluid condition Low Reynolds Number < Experimental study necessary. Modeling of Performances Implementation into Optimisation framework High speed propeller necessary to build and optimise the electrical chain Mass of the motor and converter  1/rotation speed For a given power, I batteries  1/rotation speed

7 Tests on propellers Results in Hovering Best working point Diametre = 50 cm Thrust = 500 g P mechanical = 26 W Rotation speed = 1630 rpm Figure of merit = 0.6

8 Tests on converters and motors Brushless Motors : Inner rotor (high speed, low torque): gearbox necessary. Outer rotor (low speed, high torque). Test on Model motor AXI speed controller Jeti advance 18-3P (Direct drive) Working point: speed > 3500 rpm for efficiency > 60 % Gearbox (still !) needed…

9 Tests on batteries Our application : high power and energy density required Lithium Chemistry ( 3,6 V; I discharge >2 C; Energy density = 140 Wh/kg) Kind of battery Nb of elements Mass (g) Av Voltage 1 Element (V) (at 1 C) Capacity (Ah) Max Continuous discharge current (A) P max continous (W) Energy density (Wh/kg) Li-Ion Panasonic CGR A 31413,61,83 2,18 C = 4 A 35 (32 min) 135 Li-Poly Kokam SLPB ,63 1,66 C = 5 A 30,5 (35 min) 132 Tests results for 2 suitable batteries:

10 Global traction chain test in hovering 50 cm Results: Autonomy = 33 min Payload = 141 g P electrical = 35 W Efficiency = 65 % Off-the-shelf components can fullfill the specification sheet but… Important improvements are possible: On the propeller mass (85 g at present). On the propeller speed (for motor and converter optimisation). On the motor (better torque for direct drive and high efficiency).

11 Design of a new dedicated planar motor Objective : build a brushless motor adjusted to the propeller Specification sheet : mechanical power and low rotation speed Model : based on the electromotive force created by a conductor under a magnetic flux variation Software : Optimisation goal : minimise the mass of the motor and maximise its efficiency Constraints : width and thickness of the windings, diametre of the stator and rotor, etc. Results : Pareto curves (point = minimised mass for a given efficiency)

12 Structure Disk rotor Planar stator Rotor sandwich Stator sandwich Single gap structure

13 Structure choice 30 g 20 g -10 % -7 %

14 Optimisation of the entire chain Propeller modelMotor model Pj = R.i 2, (Joule losses) e = B.L.v, (e.m.f) Pin = e.i + Pj, efficiency = Pout/Pin mass = .V Batteries model Batteries data base Voltage, Current, Energy, Power, Mass Propellers data base , k, Diameter, Mass Overall mass Autonomy The best solution Objectives : maximise the autonomy and the payload for a given overall mass

15 Conclusion Carefully selected off-the-shelf components can presently comply with the specification sheet if smartly associated but multi-constraint optimisation is necessary dedicated planar motors can enhance the performances

16 Macro Fibre Composite actuators as an alternative to drive morphing structures Applications : flapping wings, flaps,… Threshold of 770 V, deflection of 20 mm To be optimised in terms of number, optimal speed, MFC dimensions control to be applied to UAV Perspectives

17 Thank you for your attention ! Any questions ? Any answers ?