Spektrum Firma 1900kv Sensorless Brushless Motor. 
Specifications:
Bushing Or Bearing: Bearings
Cells: 3-6S LiPo
Connector Type: D4
Efficiency: 86%
Input Voltage: 11.1 - 22.2V (25.2V max)
Maximum Continuous Current: 60A
Motor Design: Outrunner
Number of Poles: 4
Outer Diameter: 1.6 in (42 mm)
Overall Length: 2.9 in (74 mm)
Product Weight: 14.67 oz (416 g)
RPM: 29100 @ 15V
Shaft Diameter: 0.197 in (5 mm)
Shaft Length: 0.73 in (18.5 mm)