Cobra CM-2820/16 740Kv Motor Propeller Data
Magnets Motor Wind Motor Kv No-Load Current Motor Resistance I Max P Max (4S)
14-Pole 16-Turn Delta 740 RPM/Volt Io = 0.92 Amps @ 15v Rm = 0.074 Ohms 35 Amps 520 W
 
Stator Outside Diameter Body Length Total Shaft Length Shaft Diameter Motor Weight
12-Slot 35.0 mm,  1.378 in. 46.4 mm,  1.827 in. 52.6 mm,  2.071 in. 5.00 mm,  0.197 in. 146 gm,   5.15 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 0.79 A 0.92 A 1.08 A 1.24 A 700 RPM/Volt @ 15V 0.074 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 12x4.5-MR 3 11.1 14.28 158.5 6,529 34.0 1171 41.31 7.39
APC 14x5.5-MR 3 11.1 22.09 245.2 5,851 30.5 1658 58.48 6.76
APC 16x5.5-MR 3 11.1 29.97 332.7 5,185 27.0 2081 73.40 6.26
GemFan 13x4.5-MR-W 3 11.1 16.52 183.4 6,353 27.1 1315 46.38 7.17
GemFan 14x4.5-MR-W 3 11.1 19.19 213.0 6,126 26.1 1505 53.09 7.07
GemFan 15x4.5-MR-W 3 11.1 20.72 230.0 5,976 25.5 1594 56.23 6.93
GemFan 16x4.5-MR-W 3 11.1 26.34 292.4 5,466 23.3 1873 66.07 6.41
RC-Timer 12x5.5-CF 3 11.1 17.19 190.8 6,283 32.7 1206 42.54 6.32
RC-Timer 13x5.5-CF 3 11.1 21.73 241.2 5,900 30.7 1432 50.51 5.94
RC-Timer 14x5.5-CF 3 11.1 27.45 304.7 5,368 28.0 1609 56.76 5.28
RC-Timer 15x5.5-CF 3 11.1 33.84 375.6 4,746 24.7 1797 63.39 4.78
 
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 10x4.5-MR 4 14.8 14.38 212.8 8,984 46.8 1259 44.41 5.92
APC 11x4.5-MR 4 14.8 17.94 265.5 8,658 45.1 1558 54.96 5.87
APC 12x4.5-MR 4 14.8 22.90 338.9 8,189 34.9 1898 66.95 5.60
APC 14x5.5-MR 4 14.8 33.65 498.0 7,143 37.2 2526 89.10 5.07
APC 16x5.5-MR 4 14.8 42.59 630.3 6,071 31.6 2938 103.63 4.66
GemFan 11x4-MR-W 4 14.8 15.83 234.3 8,843 33.5 1431 50.48 6.11
GemFan 12x4-MR-W 4 14.8 20.64 305.5 8,400 31.8 1761 62.12 5.76
GemFan 13x4.5-MR-W 4 14.8 25.34 375.0 7,965 33.9 2062 72.73 5.50
GemFan 14x4.5-MR-W 4 14.8 28.92 428.0 7,595 32.4 2335 82.36 5.46
GemFan 15x4.5-MR-W 4 14.8 31.51 466.3 7,330 31.2 2491 87.87 5.34
GemFan 16x4.5-MR-W 4 14.8 38.48 569.5 6,622 28.2 2805 98.94 4.93
RC-Timer 11x5.5-CF 4 14.8 18.47 273.4 8,602 44.8 1457 51.39 5.33
RC-Timer 12x5.5-CF 4 14.8 27.44 406.1 7,756 40.4 1902 67.09 4.68
RC-Timer 13x5.5-CF 4 14.8 33.86 501.1 7,113 37.0 2187 77.14 4.36
RC-Timer 14x5.5-CF 4 14.8 42.77 633.0 6,472 33.7 2457 86.67 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.