1 Fabrication and optimisation of an electrical motorisation for mini-UAV in hovering Nicolas...
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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
L.E.GL.E.G
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Electric propulsion chain for hoveringGlobal/elementary optimisation
• Traction
• Output power
• Rotation speed
• Figure of Merit
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• Hovering
• Dimensions
• Mass
• Autonomy
• Noise
• Payload
Specification sheet
Optimisation tool necessary !
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• Voltage
• Current
• Efficiency
• Capacity (A.h)
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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
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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 :
P
TvM
air2
mg
R.M
mgP
R
m 23
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Test bench
Propeller
Motor
Speed sensor
Thrust sensor
Torque sensor
Speed controller
Fully automated
laptop
Batteries
Ball bearings
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Tests on propellers
Dimensions (50 cm) and non compressible fluid condition
Low Reynolds Number <100000
• Experimental study necessary.• Modeling of Performances• Implementation into Pro@Design 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, Ibatteries 1/rotation speed
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Tests on propellers
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0 1000 2000 3000 4000 5000 6000 7000
Speed propeller (rpm)
Th
rust
(g
)
0.11x0.2
0.12x0.25
0.18x0.28
0.2x0.38
0.28x0.51
0.257x0.512
Results in Hovering
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100
200
300
400
500
600
700
800
0 10 20 30 40 50
Mechanical Power (W)
Th
rus
t (g
)
0.11x0.2
0.12x0.25
0.18x0.28
0.2x0.38
0.28x0.51
0.257x0.512
Best working point
• Diametre = 50 cm
• Thrust = 500 g
• Pmechanical= 26 W
• Rotation speed = 1630 rpm
• Figure of merit = 0.6
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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 221226 + speed controller Jeti advance 18-3P (Direct drive)
Working point: speed > 3500 rpm for efficiency > 60 % Gearbox (still !) needed…
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Tests on batteries
Our application : high power and energy density required
Lithium Chemistry ( 3,6 V; Idischarge >2 C; Energy density = 140 Wh/kg)
Kind of battery
Nb of elements
Mass (g)
Av Voltage1 Element
(V)(at 1 C)
Capacity(Ah)
Max Continuous discharge current (A)
P max continous
(W)
Energy density(Wh/kg)
Li-IonPanasonic
CGR-18650A
3 141 3,6 1,832,18 C= 4 A
35 (32 min)
135
Li-PolyKokamSLPB
526495
2 137 3,6 31,66 C= 5 A
30,5 (35 min)
132
Tests results for 2 suitable batteries:
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Global traction chain test in hovering
50 cm
Results:
• Autonomy = 33 min • Payload = 141 g• Pelectrical= 35 W• Efficiency = 65 %
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500
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0 5 10 15 20 25 30 35 40
Time (min)
Th
rust
(g
)
Mass of components
Payload = 141 g
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50
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150
200
250
300
350
400
450
500
550
0 5 10 15 20 25 30 35 40
Time (min)
Th
rust
(g
)
Mass of components
Payload = 141 g
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).
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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 : 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)
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Structure
Disk rotor
Planar stator
Rotor sandwich
Stator sandwich Single gap structure
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0
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10
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20
25
30
35
20 40 60 80 100efficiency (%)
mas
s (g
)
structure 1
structure 2
structure 3
Structure choice
30 g
20 g
-10 %
-7 %
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Optimisation of the entire chain
m
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k
mP
Propeller model Motor modelPj = R.i2, (Joule losses)
e = B.L.v, (e.m.f)
Pin = e.i + Pj,
efficiency = Pout/Pin
mass = .V
Batteries model
Batteries data baseVoltage, Current,
Energy, Power, MassPropellers data base, k, Diameter, Mass
Overall mass Autonomy
The best solution
Objectives : maximise the autonomy and the payload for a given overall mass
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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
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• 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
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Thank you for your attention !
Any questions ?Any answers ?