Cobra CM-2217/20 Motor Propeller Data
Magnets Motor Wind Motor Kv No-Load Current Motor Resistance I Max P Max (3S)
14-Pole 20-Turn Delta 950 RPM/Volt Io = 0.53 Amps @ 12v Rm = 0.188 Ohms 20 Amps 220 W
 
Stator Outside Diameter Body Length Total Shaft Length Shaft Diameter Motor Weight
12-Slot 27.0 mm,  1.063 in. 33.0 mm,  1.299 in. 35.1 mm,  1.382 in. 3.17 mm,  0.125 in. 76 gm,   2.68 oz
 
Test Data From Input 10.0 V 12.0 V 14.0V 16.0V Measured Kv value Measured Rm Value
Sample Motor Io Value 0.49 A 0.53 A 0.58 A 0.63 A 890 RPM/Volt @ 10v 0.188 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 10x4.5-MR 3 11.1 11.83 131.3 7,536 32.1 875 30.86 6.66
APC 11x4.5-MR 3 11.1 14.00 155.4 7,107 30.3 1012 35.70 6.51
APC 12x4.5-MR 3 11.1 16.98 188.5 6,507 27.7 1168 41.20 6.20
APC 14x5.5-MR 3 11.1 22.02 244.4 5,324 27.7 1322 46.63 5.41
GemFan 8x4.5-MR 3 11.1 8.81 97.8 8,147 34.7 633 22.33 6.47
GemFan 9x4.7-MR 3 11.1 9.96 110.6 7,926 35.3 731 25.79 6.61
GemFan 10x4.5-MR 3 11.1 13.84 153.6 7,174 30.6 935 32.98 6.09
GemFan 11x4.7-MR 3 11.1 16.54 183.6 6,619 29.5 1098 38.73 5.98
GemFan 12x4.5-MR 3 11.1 19.02 211.1 6,085 25.9 1099 38.77 5.21
GemFan 10x4-MR-W 3 11.1 12.28 136.3 7,448 28.2 855 30.16 6.27
GemFan 11x4-MR-W 3 11.1 13.11 145.5 7,307 27.7 963 33.97 6.62
GemFan 12x4-MR-W 3 11.1 16.17 179.5 6,671 25.3 1115 39.33 6.21
GemFan 13x4.5-MR-W 3 11.1 18.61 206.6 6,120 26.1 1225 43.21 5.93
GemFan 14x4.5-MR-W 3 11.1 20.41 226.6 5,725 24.4 1297 45.75 5.72
 
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 17.98 266.1 9,185 39.1 1341 47.30 5.04
APC 11x4.5-MR 4 14.8 20.42 302.2 8,504 36.2 1506 53.12 4.98
GemFan 8x4.5-MR 4 14.8 13.48 199.5 10,170 43.3 997 35.17 5.00
GemFan 9x4.7-MR 4 14.8 14.94 221.1 9,847 43.8 1160 40.92 5.25
GemFan 10x4.5-MR 4 14.8 20.22 299.3 8,603 36.7 1389 49.00 4.64
GemFan 10x4-MR-W 4 14.8 18.23 269.8 9,180 34.8 1323 46.67 4.90
GemFan 11x4-MR-W 4 14.8 19.17 283.7 8,876 33.6 1426 50.30 5.03
   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.