# ELECTRIFICATION by wanghonghx

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```									ELECTRIFICATION
ELECTRIFICATION
   Introduction
   Basics of electric motors
   Brushed motors, Brushless Out Runner motors
   Motor Constants
   Choosing a Motor with makers data
   Interpreting makers data
   Rules of thumb are just that and not theoretical
   Summary
   Useful Web sites
The Coil

Magnetic field of a wire
The Coil

 One loop's magnetic field
The Coil

 A simple electromagnet
An Electric Motor

 Electromagnet in a horseshoe magnet
An Electric Motor

 Parts of an electric motor
An Electric Motor

 The commutator and coils rotates between two
magnets. This is a three pole motor
Brushless Outrunner Motor
By Torcman ®

 The coils are stationary the casing for the
magnets around the periphery rotates.
Brushless Outrunner Motor

 Torcman Motor                  14 magnets = 14 Poles
Magnetic field goes around 7 times for 1 rev of Outrunner
Outrunner type motors have more torque than same size brushed motor
Electromechanical motor constants
   The geometric arrangement of the magnetic circuit and winding defines in
detail how the motor converts the electrical input power (current, voltage)
into mechanical output power (speed, torque). Two important
characteristic values of this energy conversion are the speed constant kn
and the torque constant kM.

   The speed constant combines the speed n (rpm) with the voltage induced
in the winding Uind (Volt). Uind is proportional to the speed; the following
applies:
n = kn . Uind

   Similarly, the torque constant links the mechanical torque M (Newton)
with the
electrical current I (Amp).
M = kM . I

   The speed and torque constant are not independent. The following
applies:
kn . kM = 60 / 2π

   Efficiency = Output power / Input power hence:
η = 2π/60 . n . M / U . I
Electromechanical motor constants
Power balance Pin= Ploss + Pmech
= U.I = R.I2 + M.n.2π/60      R=Resistance
U.M/km = R.(M/km)2 + M.n.2π/60
N = U. 60/ 2π.km.– R.M.60/2π.km2
But kn . km = 60 / 2π

   In the speed-torque diagram, the
output power is equivalent to the
area of the rectangle below the
speed-torque line. This rectangle
and, thus, the output power, is
greatest at half stall torque and half
Choosing A Motor
Glow Motor
Rated Power               Practical Power      Propeller
Capacity
cu in       cc          Watts      BHP      @ RPM        Watts       @ RPM        in

0.10        1.8          200       0.27       17000       100        13027      7X4

0.15        2.5          305       0.41       17000       120        12628      8X6

0.25        4.1          447       0.60       15000       220         11843     9X5

RULE OF THUMB
Watts/Kg           Performance
77           Sedate Hand Launch Powered Glider
110           Rise of Ground Loops and rolls
>175          Aerobatic full 3D vertical take off feasible

! Max Rivers who distributes Torcman suggests twice as much power !
Choosing A Motor
 If the model weighs 300 g and you want it to be 3D
capable we need > 52 Watt.
 That determines the size of motor a little bigger is a good
idea say 60 Watt.
 How many cells will determine the voltage.
 Choose a propeller to absorb the power.
Remember Watts = Volts X Amps
 Choose the speed controller to suit with the current
 Big propellers turn slower. Look for a lower kv in the same
motor size.
 Lower kv means more turns or windings.
 Ducted fans want high RPM so less turns are wanted
 AXI give very useful data
Choosing A Motor
 This data is for the 2208/34
Propeller          Battery         I Amp       RPM        U Volt      P in      Efficiency %

9X3.75          2x Li-Poly          5.5       6190         7.1        39             79

9X3.75          3x Li-Poly          8.8       7880         9.6        84             75

10X4.75          2x Li-Poly          7.8       4820         6.6        51             70

9X6           2x Li-Poly          7.8       6190         6.6        51             70

8.5X5           7 Ni Cad           4.9       6870         7.6        37             80

8.5X5           8 Ni Cad           5.8       7510         8.4        48             79

8.5X5          10 Ni Cad           7.6       8640        10.0        76             77

8X6            7 Ni Cad           6.2       6140         7.3        45             77

8X6            8 Ni Cad           7.3       6660         8.1        59             75

9.5X5           7 Ni Cad           6.9       5820         7.2        49             74

Notice how the voltage is not consistent, the volt drop in the battery increases with current drain.
Useful Information or not?
POWER AND THRUST FOR AN APC 8X6 Propellor                                                     8 X 6 Propellor RPM v Thrust

1000
15000                                                 900

900
14000                                                 800

800
13000                                                 700

700
12000                                                 600
600

11000                                                 500

Thrust g

Thrust g
RPM
RPM

500
Thrust g
10000                                                 400
400

9000                                                  300
300

8000                                                  200
200

7000                                                  100                                     100

6000                                                   0                                        0
0          50    100    150    200   250    300                                         5000   7000        9000      11000      13000
Watts                                                                                  RPM

      Thrust data is for the static condition, because of drag and wind speed,
model shape, it is possibly only of interest for prop hanging indoors
Choosing A Motor
Specification AXI 2208/34
If model weighs 300 g this
Voltage range                6-10 cells
data tells us the motor
2-3xLi-Poly
should work, but we cannot
kn RPM per Volt              1,080 RPM/V
tell much more without using
Max. Efficiency              81%                     maths!
Max. Efficiency Current      4-7 A (>74%)
kn is given presumably at no
No load Current @ 8 V        0.35 A
Using the formula we can
Internal resistance          260 mohm
predict the speed at any
Dimensions                   27,7x26 mm              torque and the power
Shaft Diameter               3,17 mm
(M.n = P watts).
Weight                       45 g
Of course we still need to
Recomended model             200 - 500 g
weight                                               know what power is needed
Propeller range              2xLi-Poly prop 10"x5"
for a given propeller.
3xLi-Poly prop 9"x4"
10 cells prop 8,5"x5"
Choosing A Motor
POWER AND THRUST FOR AN APC 8X6 Propellor

   So we know the voltage, the
15000                                             900
power, the rpm a motor will
14000                                             800
deliver now we need some
propeller data. If everything
13000                                             700                             matches that is the motor to buy!

12000                                             600
   Another rule of thumb for 6~9
11000                                             500
inch propellers:-

Thrust g
RPM
RPM

Thrust g
10000                                             400
   U volt constant then 1 inch less
diameter reduces power by 25%,
9000                                              300
RPM goes up 5%, thrust is down
8000                                              200
40 %. The converse is true for 1
inch bigger diameter.
7000                                              100

   1 inch less pitch reduce power by
6000                                               0
0      50    100    150    200   250    300
10% at same RPM.
Watts
Choosing A Motor

 Warning about - Rule of thumb
 Do not blame me! They are inaccurate!
 The idea is to get a handle on how things
relate to one another.
Choosing A Motor
RPM Vs Power

120

This data was derived
100
theoretically using the
80
relationship that
APC 10x4,7
APC 11x4,7   power and rpm are
connected by a 3√
Power

GWS 0843
60
GWS 0947
GWS 1260
40                                                     GWS 1280

20

0
0   2000   4000   6000   8000    10000   12000
RPM
Electrification
Summary
 Brushless motors are more efficient and more
powerful than the same size brushed motor.
 Brushless Motors are different not necessarily
better, it depends on what you want.
 More turns means less speed and more
torque.
 If you copy someone else make sure they tell
you exactly what they have, look at the specs
and confirm.
Electrification
Summary
   If you go your own way
-   Estimate the model weight.
-   Decide how you would like it to fly.
-   Match the motor to the power needed.
-   Decide on battery type
-   Pick a propeller to absorb the power.
Web Sites

 www.megamotor.cz/en/novinky.phtml
 www.kb-modell.de
 www.modelmotors.cz/index.php?id=en&nc=domu
 http://www.torcman.de/index.htm

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