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# Fast Electric Calculator - homepage.ntlworld.com by nyut545e2

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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,

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

0.96 Volts

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.

, 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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