<p>This sensor, used in conjunction with a telemetry enabled transmitter/receiver, is used to indicate the number of rotations (propeller, rotor, etc. ) of the item to which it is attached. The number of rotations of a model in the sky is a system which can be checked with a transmitter etc. To maximize your enjoyment, and to ensure proper sensing, please read through the manual thoroughly.</p><p><br></p><p>The SBS-01RO is not optimal for helicopter use due to the large distance between the rotor and sensor, as a result, the reading can be unstable. We recommend the SBS-01RM magnetic sensor be utilized for helicopters.</p><p><br></p><p>Use: RPM Sensor</p><p>Length: 160 mm</p><p>Weight: 4.9 g</p><p>Voltage: DC3.7 ～ 7.4V</p><p>Range: 360 ～ 300,000 RPM/blades</p>