ELECTRIFICATION by wanghonghx

VIEWS: 10 PAGES: 23

									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
     no-load speed.
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
Max. loading                 8 A / 60 s              load.
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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