Cobra CM-2820/32 350Kv Motor Propeller Data
Magnets Motor Wind Motor Kv No-Load Current Motor Resistance I Max P Max (6S)
14-Pole 32-Turn Delta 350 RPM/Volt Io = 0.33 Amps @ 15v Rm = 0.200 Ohms 20 Amps 450 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 0.30 A 0.33 A 0.36 A 0.39 A 353 RPM/Volt @ 15V 0.200 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 5 18.5 9.39 173.7 5,414 28.2 1404 49.52 8.08
APC 16x5.5-MR 5 18.5 11.38 210.5 4,921 25.6 1862 65.68 8.84
APC 18x5.5-MR 5 18.5 16.61 307.3 4,526 23.6 2194 77.39 7.14
GemFan 15x4.5-MR-W 5 18.5 8.70 161.0 5,489 23.4 1320 46.56 8.20
GemFan 16x4.5-MR-W 5 18.5 11.73 217.0 5,139 21.9 1670 58.91 7.70
RC-Timer 13x5.5-CF 5 18.5 9.15 169.3 5,434 28.3 1214 42.82 7.17
RC-Timer 14x5.5-CF 5 18.5 12.31 227.7 5,073 26.4 1450 51.15 6.37
RC-Timer 15x5.5-CF 5 18.5 15.67 289.9 4,612 24.0 1681 59.29 5.80
RC-Timer 16x5.5-CF 5 18.5 17.86 330.4 4,354 22.7 1847 65.15 5.59
RC-Timer 17x5.5-CF 5 18.5 19.12 353.7 4,123 21.5 1930 68.08 5.46
 
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 6 22.2 7.82 173.6 6,830 29.1 1292 45.57 7.44
APC 14x5.5-MR 6 22.2 12.50 277.5 6,231 32.5 1889 66.63 6.81
APC 16x5.5-MR 6 22.2 17.41 386.5 5,587 29.1 2442 86.14 6.32
APC 18x5.5-MR 6 22.2 21.02 466.6 5,048 26.3 2808 99.05 6.02
GemFan 13x4.5-MR-W 6 22.2 9.03 200.5 6,676 28.4 1426 50.30 7.11
GemFan 14x4.5-MR-W 6 22.2 10.64 236.2 6,459 27.5 1703 60.07 7.21
GemFan 15x4.5-MR-W 6 22.2 11.58 257.1 6,329 27.0 1804 63.63 7.02
GemFan 16x4.5-MR-W 6 22.2 15.10 335.2 5,875 25.0 2189 77.21 6.53
RC-Timer 12x5.5-CF 6 22.2 9.60 213.1 6,600 34.4 1339 47.23 6.28
RC-Timer 13x5.5-CF 6 22.2 12.41 275.5 6,241 32.5 1644 57.99 5.97
RC-Timer 14x5.5-CF 6 22.2 16.22 360.1 5,738 29.9 1900 67.02 5.28
RC-Timer 15x5.5-CF 6 22.2 20.34 451.5 5,126 26.7 2113 74.53 4.68
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.