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Fabrication and optimisation of an electrical motorisation for mini-UAV in hovering

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. Specification sheet. Hovering Dimensions Mass Autonomy

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Fabrication and optimisation of an electrical motorisation for mini-UAV in hovering

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

  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 Ball bearings Motor Torque sensor Speed controller Speed sensor Batteries Fully automated laptop Thrust sensor

  6. Tests on propellers • Dimensions (50 cm) and non compressible fluid condition • Low Reynolds Number <100000 • Experimental study necessary. • Modeling of Performances • Implementation into Pro@DesignOptimisation framework High speed propeller necessary to build and optimise the electrical chain Mass of the motor and converter a 1/rotation speed For a given power, Ibatteriesa 1/rotation speed

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

  8. Tests on converters and motors Inner rotor (high speed, low torque): gearbox necessary. Outer rotor (low speed, high torque). Brushless Motors : Test on Model motor AXI 221226 + 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; Idischarge >2 C; Energy density = 140 Wh/kg) Tests results for 2 suitable batteries:

  10. Global traction chain test in hovering 50 cm • Results: • Autonomy = 33 min • Payload = 141 g • Pelectrical= 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 rotationspeed Model : based on the electromotive force created by a conductor under a magnetic flux variation Software : Pro@Design 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 Single gap structure Stator sandwich

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

  14. Propeller model Motor model Pj = R.i2, (Joule losses) e = B.L.v, (e.m.f) Pin = e.i + Pj, efficiency = Pout/Pin mass = r.V Batteries data base Voltage, Current, Energy, Power, Mass Propellers data base s, k, Diameter, Mass Optimisation of the entire chain Objectives : maximise the autonomy and the payload for a given overall mass Autonomy Overall mass Batteries model The best solution

  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. Perspectives • 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

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

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