HK 2221 V2 Series 2221-6 2221-8 2221-10 2221-12 2221-1630 Kv (rpm/V) 4400 3595 3000 2580 1630 Max Power (W) 525W 475W 440W 400W 530W Max Amp (15sec) 52A 45A 42A 38A 30A Max Efficiency 85% 85% 85% 85% 85% Io (No load A) 2.89A 2.31A 1.79A 1.5A 0.71A Rm (Resistance) 0.016Ohm 0.024Ohm 0.031Ohm 0.038Ohm 0.079Ohm Shaft Diameter 3.17mm 3.17mm 3.17mm 3.17mm 3.17mm Gearbox N/A N/A N/A N/A N/A Motor Diameter 28mm 28mm 28mm 28mm 28mm Motor Length 33.6mm 33.6mm 33.6mm 33.6mm 38mm Motor Weight 79g 79g 79g 79g 79g Built in Fan Yes Yes Yes Yes Yes Max Rpm 48,000 48,000 48,000 48,000 48,000 Poles 6 6 6 6 6 Case Outrunner Outrunner Outrunner Outrunner Outrunner ESC Timing 20-25 deg 20-25 deg 20-25 deg 20-25 deg 20-25 deg ESC Switching Freq. 8-16KHz 8-16KHz 8-16KHz 8-16KHz 8-16KHz