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Fast Electric Calculator - homepage.ntlworld.com

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					Fast Electric Calculator
     This spread sheet has been produced to take the effort out of those tricky fast
     electric calculations. To use the sheet simply enter the relevant values into the
     white boxes and the answer will appear in the red box. I have tried to include as
     many formulas as possible, but if you require something that is not listed,
     please drop me an email.

                              Weight Conversion
     Enter weight in grams                        Enter weight in Ounces
           500 g                                         10 oz

     Weight in ounces is                          Weight in Grams is
         17.64 oz                                      284 g

     Weight in pounds is
          1.10 lb.



                              Length Conversion
     Enter length in inches                       Enter length in mm
             12 inches                                   300 mm

     Length in mm is                              Length in inches is
         304.8 mm                                     11.81 inches



                              Speed Conversion
     Enter speed in miles per hour                Enter speed in kilometres per hour
             31 mph                                       50 km/h

     Speed in Kilometres per hour Is              Speed in miles per hour is
          50.0 km/h                                    31.0 mph

     Speed in metres per second is                Speed in metres per second is
          13.9 m/s                                     13.9 m/s

     Speed in feet per second is                  Speed in feet per second is
          45.5 ft/s                                    45.4 ft/s


                              Current Calculator

                                       Enter battery capacity in mAH
                                              800 mAH

                                       Enter run time in seconds
                                              300 seconds
                                Average current is
                                      9.6 Amps



                    Cell Pack Voltage
                                Enter number of cells
                                        7 cells

                                Nominal Voltage is
                                      8.4 v


                    Power and Resistance
                                Enter Volts
                                       8.4 v

                                Enter Current
                                       25 Amps

                                Power is
                                      210 Watts

                                Resistance is
                                    0.336 Ohms          Note: 1 Milliohm = 0.001Ohms




                               Volt Drop
                                Enter Current                    You can use this
                                       60 Amps                   calculation to
                                                                 work out the voltage
                                Enter Resistance                 drop across an ESC.
Note: 1 Milliohm = 0.001Ohms        0.002 Ohms

                                Volt drop across resistance is
                                      0.12 Volts


                                Cell Duration
                                Enter Cell Capacity
                                     2000 mAh

                                Enter Discharge current
                                        24 Amps

                                Cell(s) will last
                                       300 Seconds


          Cell pack voltage and power output under load
                                   Enter number of cells
                                           7 Cells

                                   Enter discharge current
                                           60 Amps

                                   Enter internal resistance of cell
                                           4.0 Milliohms

                                   Cell voltage under load is
                                         0.96 Volts

                                   Pack voltage under load is
                                        6.72 Volts

                                   Pack power output is
                                         403 Watts



                                    Propeller Pitch
                                   Pitch ratio
          Enter diameter           Octura Props: X4=1.4:1, X6=1.6:1, 17=17:1, 19=1.9:1, 20=2:1, 21=2.1:1
                  29 mm
                                   Prather Props are between 1.5 and 1.6:1
          Enter pitch ratio
                 1.2 :1            Graupner: K and P series = 1.2:1 , S series = 1.4:1

          Propeller pitch is       Amps props are around 1.5:1
               34.8 mm


                      Speed Prediction
                      Enter pitch of propeller
                                65 mm

                      Enter Revs Per Minute
                            20000 RPM                      Prop Slippage Guide
                                                           Monohull: typically 25%
                      Prop slippage                        Scale Hydro: typically 20%
                                25 %                       Rigger: typically 15%

                      Speed is
                                 36 mph
                                 59 km/h




                      Speed Calculation
Distance between check points                              Distance between check points
       60 Metres                                                 500 Feet
Time taken to pass between check points           Time taken to pass between check points
       4.2 Seconds                                       10 Seconds

Speed is                                          Speed is
     31.9   MPH                                        34.0    MPH
     51.4   Km/h                                       54.9    Km/h
     14.3   metres/second                              15.2    metres/second
     46.9   feet/second                                50.0    feet/second


                                      Motor RPM
Enter boat speed                                  Enter boat speed
      51.4 Km/h                                         31.9 MPH

Enter pitch of propeller                          Enter pitch of propeller
        65 mm                                             65 mm

Enter gear ratio                                  Enter gear ratio
         2 :1 (for direct drive enter 1)                   2 :1 (for direct drive enter 1)

Enter prop slippage                               Enter prop slippage
        20 %                                              20 %

Motor speed is:                                   Motor speed is:
   31631 RPM                                         31663 RPM

            Prop Slippage Guide
            Monohull: typically 25%
            Scale Hydro: typically 20%
            Rigger: typically 15%


                                      Discharger Design
Enter number of cells                             Common resistor values (Ohms):
        7 Cells                                        0.1        0.22      0.47
                                                      0.68           1       1.5
Enter required discharge current                         2.7          3.3         3.9
        10 Amps                                          5.6          6.8         8.2

Resistor value is:
      0.84 Ohm(s)                                 For example: .84 ohms @ 98w you could use 4 x .22
                                                  Ohm 25w resistors in series (=.88 Ohms), 4 x .33 Ohm
Minimum resistor power rating is:                 25w resistors in parallel (=.825 Ohms) or even 10 x 8.2
      98 Watts                                    Ohm 10w resistors in parallel (=.82 Ohms)
out of those tricky fast
relevant values into the
I have tried to include as
g that is not listed,
work out the voltage
drop across an ESC.




put under load
, 17=17:1, 19=1.9:1, 20=2:1, 21=2.1:1
o pass between check points




1 (for direct drive enter 1)




                               0.56
                                2.2
                                4.7
                                10


: .84 ohms @ 98w you could use 4 x .22
sistors in series (=.88 Ohms), 4 x .33 Ohm
s in parallel (=.825 Ohms) or even 10 x 8.2
sistors in parallel (=.82 Ohms)

				
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