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Version: Version 2.1.0

RPM Measurement

In order to use the Governor or RPM filters (and why wouldn't you!!) you must measure the RPM. There are two options for this:

  • RPM sensor
  • Bi-directional D-shot
info

RPM can sometimes also be read via ESC telemetry. However, this is at a refresh frequency that is too slow to be used for filtering of governing.

caution

RPM filtering is used to remove frequencies related to the rotating components. This allows a much higher tune; HOWEVER!! If the helicopter is flown in an OverSpeed condition the rotation of the one way bearing means that the RPM measurement will not be correct. If the helicopter is tuned too critically this could mean the helicopter could become out of tune resulting in unwanted oscillations.

note

Frequency Sensor​

Typically it is used when the RPM is not available via ESC telemetry. Only BLHeli_32, some BLHeli_S and APD F3 ESCs support Dshot/KISS telemetry, so this feature is needed with a wide range of traditional ESCs.

The RPM signal is used in multiple places in the FC, e.g. in the PID control, the governor and the RPM-filter. If these features are not needed, then there is no need for the frequency sensor either.

An electrical frequency signal is provided by some ESCs, e.g. Hobbywing with the "yellow" wire. Or it can come from an RPM sensor, which is converting the motor three-phase voltages into a frequency signal - e.g. Hobbywing RPM sensor. Please refer to your ESC's or sensor's manuals how to connect them correctly.

Note about the Hobbywing RPM sensor: it's safest to power it with 3.3V, as the input voltage of the sensor is also the output voltage of the RPM signal it generates. All inputs on a STM32 MCU tolerate 3.3V, and some will also accept 5V. But if you're using a 8.4V BEC to power the sensor, you'll likely damage the MCU.

Up to two frequency sensors are supported, for acquiring motor #1 and motor #2 speed.

If both Frequency Sensor and telemetry RPM signals are available, the Frequency Sensor has precedence.

Connection​

Plug the ESC RPM wire (often yellow wire) or separate RPM sensor (Hobbywing RPM etc) into the FC RPM input.

Frequency input

Configuration​

Then the frequency sensor can be turned ON with the feature flag located on the Motors tab.

frequency_2