Hobbywing rpm sensor this hobbywing rpm sensor detects the voltage changes at the wires of brushless motor, and then outputs the rpm signal. This rpm sensor can work with some speed control systems for helicopters. And one of its typical applications is to work as the rpm sensor for v-bar system made by mikado. It is included as standard equipment with the platinum-120a-hv, platinum-70a-hv, flyfun-100a-hv and flyfun-80a-hv esc's. The hobbywing rpm sensor is compatible with any firmware of the above esc's, that means if you use hobbywing rpm sensor, the above esc's are always compatible with v-bar governor function. Spec check: size: 23mm(l)*10mm(w)*2mm(h) weight: 6g (input and output wires are included) working voltage: 3. 5v to 8. 4v(1s to 2s lipo) current: 1 to 5ma voltage range of the motor wires: 2 to 14s lipo rpm range (for 2 poles brushless motor): 1000rpm to 300000rpm working temperature: 0 to 50 celsius degree or 32 to 122 fahrenheit degree (hw86060041)