Cobra CM-3520/20 480Kv Motor Propeller Data
Magnets Motor Wind Motor Kv No-Load Current Motor Resistance I Max P Max (6S)
14-Pole 20-Turn Delta 480 RPM/Volt Io = 0.68 Amps @ 15v Rm = 0.069 Ohms 32 Amps 710 W
 
Stator Outside Diameter Body Length Total Shaft Length Shaft Diameter Motor Weight
12-Slot 43.0 mm,  1.693 in. 52.0 mm,  2.047 in. 55.6 mm,  2.189 in. 5.00 mm,  0.197 in. 234 gm,   8.25 oz
 
Test Data From Input 12.0 V 15.0 V 18.0V 21.0V Measured Kv value Measured Rm Value
Sample Motor Io Value 0.63 A 0.68 A 0.74 A 0.80 A 465 RPM/Volt @ 15V 0.069 Ohms
 
Prop Prop Li-Po Input Motor Input Prop Pitch Speed Thrust  Thrust Thrust Eff.
Manf. Size Cells Voltage Amps Watts RPM in MPH Grams Ounces Grams/W
APC 14x5.5-MR 4 14.8 14.66 217.0 5,835 30.4 1644 57.99 7.58
APC 16x5.5-MR 4 14.8 21.32 315.5 5,407 28.2 2260 79.72 7.16
APC 18x5.5-MR 4 14.8 27.16 402.0 5,039 26.2 2776 97.92 6.91
GemFan 15x4.5-MR-W 4 14.8 13.45 199.1 5,930 25.3 1531 54.00 7.69
GemFan 16x4.5-MR-W 4 14.8 18.07 267.4 5,622 24.0 1970 69.49 7.37
RC-Timer 13x5.5-CF 4 14.8 14.22 210.5 5,858 30.5 1408 49.67 6.69
RC-Timer 14x5.5-CF 4 14.8 19.33 286.1 5,523 28.8 1714 60.46 5.99
RC-Timer 15x5.5-CF 4 14.8 26.13 386.7 5,092 26.5 2104 74.22 5.44
RC-Timer 16x5.5-CF 4 14.8 29.88 442.2 4,898 25.5 2360 83.25 5.34
RC-Timer 17x5.5-CF 4 14.8 33.01 488.5 4,675 24.3 2513 88.64 5.14
 
Prop Prop Li-Po Input Motor Input Prop Pitch Speed Thrust  Thrust Thrust Eff.
Manf. Size Cells Voltage Amps Watts RPM in MPH Grams Ounces Grams/W
APC 12x4.5-MR 5 18.5 12.93 239.2 7,558 32.2 1610 56.79 6.73
APC 14x5.5-MR 5 18.5 21.06 389.6 6,976 36.3 2424 85.50 6.22
APC 16x5.5-MR 5 18.5 30.10 556.9 6,361 33.1 3233 114.04 5.81
APC 18x5.5-MR 5 18.5 37.45 692.8 5,855 30.5 3781 133.37 5.46
GemFan 13x4.5-MR-W 5 18.5 14.67 271.4 7,431 31.7 1776 62.65 6.54
GemFan 14x4.5-MR-W 5 18.5 17.47 323.2 7,230 30.8 2106 74.29 6.52
GemFan 15x4.5-MR-W 5 18.5 19.22 355.6 7,089 30.2 2274 80.21 6.40
GemFan 16x4.5-MR-W 5 18.5 25.44 470.6 6,711 28.6 2860 100.88 6.08
RC-Timer 12x5.5-CF 5 18.5 15.81 292.5 7,340 38.2 1658 58.48 5.67
RC-Timer 13x5.5-CF 5 18.5 20.93 387.2 6,984 36.4 2056 72.52 5.31
RC-Timer 14x5.5-CF 5 18.5 28.05 518.9 6,490 33.8 2467 87.02 4.75
RC-Timer 15x5.5-CF 5 18.5 37.23 688.8 5,872 30.6 2835 100.00 4.12
 
Prop Prop Li-Po Input Motor Input Prop Pitch Speed Thrust  Thrust Thrust Eff.
Manf. Size Cells Voltage Amps Watts RPM in MPH Grams Ounces Grams/W
APC 11x4.5-MR 6 22.2 13.67 303.5 9,096 38.8 1770 62.43 5.83
APC 12x4.5-MR 6 22.2 17.53 389.2 8,780 37.4 2217 78.20 5.70
APC 14x5.5-MR 6 22.2 28.16 625.2 7,973 41.5 3260 114.99 5.21
APC 16x5.5-MR 6 22.2 37.27 827.4 7,548 39.3 4100 144.62 4.96
GemFan 12x4-MR-W 6 22.2 15.67 347.9 8,930 33.8 2020 71.25 5.81
GemFan 13x4.5-MR-W 6 22.2 19.41 430.9 8,639 36.8 2393 84.41 5.55
GemFan 14x4.5-MR-W 6 22.2 22.93 509.0 8,363 35.6 2838 100.11 5.58
GemFan 15x4.5-MR-W 6 22.2 25.48 565.7 8,180 34.9 3059 107.90 5.41
GemFan 16x4.5-MR-W 6 22.2 32.79 727.9 7,647 32.6 3714 131.01 5.10
RC-Timer 11x5.5-CF 6 22.2 13.88 308.1 9,081 47.3 1637 57.74 5.31
RC-Timer 12x5.5-CF 6 22.2 21.68 481.3 8,436 43.9 2257 79.61 4.69
RC-Timer 13x5.5-CF 6 22.2 28.52 633.1 7,945 41.4 2755 97.18 4.35
RC-Timer 14x5.5-CF 6 22.2 36.74 815.6 7,326 38.2 3163.5 111.59 3.88
Propeller Chart Color Code Explanation
   The prop is to small to get good performance from the motor. (Less than 50% power)
   The prop is sized right to get good power from the motor. (50 to 80% power)
   The prop can be used, but full throttle should be kept to short bursts. (80 to 100% power)
   The prop is too big for the motor and should not be used. (Over 100% power)
PLEASE NOTE:
The Data contained in this Prop Chart is based on actual measurements, taken in a controlled test environment, at an altitude of
512 feet above sea level.  The test voltages used are based on the standard output of a Li-Po battery under load, which is 3.70 volts
per cell.  If you are using a battery that is larger in capacity than normal, or has a very high C-rating, then your actual voltages will
be higher than those shown in the chart, and this will result in a higher current and power value for every prop used.  You should
always test your actual power system with a watt meter before flying your model to make sure that you are not exceeding the 
recommended current and power ratings of the motor being used.  The prop recommendations in this chart assume that the motor
receives adequate cooling throughout its operation.  If your motor is being used inside a cowl or fuselage, you must ensure that
the motor receives sufficient airflow, and does not get too hot during operation.  It is always best to use a prop size that pulls no
more than 80% of the motors maximum recommended current value to ensure safe operation under all conditions.