ESC Setup - rotorflight/rotorflight GitHub Wiki

Knowing the current RPM of the main motor is needed for governing it and for RPM filtering. RPM filtering is strongly recommended when using Rotorflight: it uses the RPM information to identify and filter out vibrations that are coming from the main and tail rotors.

There are three ways for obtaining the motor RPM:

  • Bidirectional DSHOT RPM telemetry
  • KISS ESC telemetry
  • Frequency sensor

1. Bidirectional DSHOT RPM Telemetry

BLHeli_32 and some BLHeli_S alternatives -like Bluejay- support bidirectional DSHOT. For helicopters it's important that braking is disabled on the ESC for the main motor, else the main motor will stop too abrupt - possibly damaging the main gear. If your helicopter doesn't support autorotation (no one way bearing), disable damped light as well. In BLHeli_32 disable Brake On Stop and enable Non Damped Mode, like this:

BLHeli_32

However, enable damping on the ESC for the tail motor if you have one. It will improve tail performance.

For BLHeli_S ESC you will need to update the firmware to Bluejay in order to use bidirectional DSHOT. Step by step details can be found Blheli_S to Bluejay.

2. KISS ESC Telemetry

KISS ESCs, like the KISS 24A and most BLHeli_32 ESCs support KISS telemetry over a seperate wire from the ESCs to the FC. The protocol has frames of 10 bytes and communicates with the FC at 115200 baud, enabling a maximum rate of 1KHz. That's enough for governing and RPM filtering. Here's more info on how to set this up.

Other ESCs may also have telemetry output. The MSRC project lists a few. However, the rate of those protocols is too slow for governing or RPM filtering. For example, the Hobbywing Platinum V3/4/5 telemetry update rate crawls at 50Hz.

3. Frequency Sensor

If your ESC doesn't support bidirectional DSHOT or KISS telemetry, you can use an RPM sensor. Hobbywing has one for brushless motors. Also, some ESCs like the Hobbywing Platinum V3/4/5 have a frequency sensor built in: the yellow wire transmits the RPM pulse signal. This page describes how to configure it.

Note that the Hobbywing RPM sensor only works safe with 3.3V. If you're using 5V to power it, it will also output 5V. And that might damage MCU pins that can't handle 5V (all FC pins can handle 3.3V). This is only an issue with the Hobbywing RPM sensor, the RPM signal from the Hobbywing ESCs is always 3.3V.