Case Study – Application of Sensorsin measuring torque and thrust produced by propellers

in small unmanned quad-rotor helicopter

???Propeller Thrust, Torque & RPM

Thrust (N) / Lift force by propeller

Torque (N-m)

)(xfF

x

k

F

kxF

F

Force Applied

Spring Const.

Spring Elongation

How to get this force in terms of electrical Signal / voltage ???

)(ForcefVoltage

Strain Gauge

Resistance

A

l

RA

lR

Property of material

Length of wire

Effective cross sectional area of wire

lR

R

l

R

l

=>

Tension

Compression

Wheatstone Bridge

inout VRR

R

RR

RV

21

2

43

4

Wheatstone Bridge

(3) (3)

(3) (3) 0

0.533

3

33

3

00.5

,

21

2

43

4

out

out

inout

in

V

V

VRR

R

RR

RV

voltsV

say

Wheatstone Bridge

(2) (4)

(4) (2)

voltsV

V

V

VRR

R

RR

RV

voltsV

say

out

out

out

inout

in

667.1

0.56

2

6

4

0.524

2

42

4

00.5

,

21

2

43

4

Full Bridge Strain Gauge

RR

R R

Tension

Compression

No Force Applied

R

R

R

R

Bending Beam Load Cell

Strain Gauge

Strain Gauge

Bending Beam Load Cell

Strain GaugeIn Tension

Strain Gaugein compression

Measuring Thrust & Torque

Measuring Thrust & Torque

Thrust

Torque

Measuring RPM

Light Sensitive Sensor

LED

Calibration of Sensors

Calibration of Sensorsy = 8E-06x3 - 0.0006x2 + 1.0108x

y = -4E-06x3 - 0.0027x2 + 2.1242x

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

0 40 80 120 160 200

MEASURED RESPONSE (A/D COUNT)

AP

PL

IED

WE

IGH

T (

gm

)

Torque Calibration CurveThrust Calibration Curve

Propeller Characteristics

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 500 1000 1500 2000 2500 3000 3500 4000 4500

RPM

TH

RU

ST

(N)

APC 7 X 8 Theoretical Result

APC 7 X 8 Dynamometer Test Result

APC 7" X 8" Slo-FLyer Prop

y = -5E-14x3 + 2E-09x2 - 6E-07x

0.0000

0.0025

0.0050

0.0075

0.0100

0.0125

0.0150

0.0175

0.0200

0.0225

0.0250

0 500 1000 1500 2000 2500 3000 3500 4000 4500

RPM

Torq

ue (N

-m)

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

2.50

0.00 5.00 10.00 15.00 20.00 25.00 30.00

POWER (watt)

TH

RU

ST

(N

)

GWS 8" X 4" (5.26 gm)Graupner 6.7" X 3.5" (4.79 gm)APC 7" X 3" (5.65 gm)Graupner 7" X 3" (12.75 gm)Master Screw 8" X 5" (11.68 gm)APC 7" X 8" (12.38 gm)

0.0000

0.0050

0.0100

0.0150

0.0200

0.00 5.00 10.00 15.00 20.00 25.00 30.00

POWER (watt)

TOR

QU

E (N

-m)

APC 7" X 8" (12.38 gm)Master Screw 8" X 5" (11.68 gm)GWS 8" X 4" (5.26 gm)Graupner 6.7" X 3.5" (4.79 gm)Graupner 7" X 3" (12.75 gm)APC 7" X 3" (5.65 gm)

Propeller DynamometerDemo