What’s RPM Filter and Bidirectional DShot

One of the biggest improvements in Betaflight 4.0 is RPM Filter and Directional DShot. In this article I will discuss what RPM Filter and Bidirectional DShot are, and what benefits they will bring to our mini quad.

RPM filter will revolutionize the filtering in Betaflight. I haven’t tried it yet, but I have been hearing positive reports from testers, I cannot wait to try it when both Betaflight and BLHeli32 become more stable.

See this post for more info about Betaflight Filters.

What are Bidirectional DSHOT and RPM Filter?

RPM filter is designed to reduce motor noise. It works by targeting motor RPM and its harmonics frequencies. The RPM data is sent from the ESC to the FC – this is where Bidirectional DShot comes into play.

Bidirectional DShot gives ESC the ability to tell the flight controller the RPM of each motor – how fast the motors are spinning in real time.

RPM Filter is not magic, it’s just a collection of notch filters. But since we can get RPM of each motor without delay, we can target and attenuate motor noise more accurately and quickly, without adding too much latency to the system.

Requirement to Run Bidirectional DSHOT and RPM Filter

Hardware: BLHeli_32 ESC and F4/F7 flight controllers.

RPM Filter is available on Betaflight 4.0, you can flash it through the configurator today.

In order to run Bidirectional DShot, you need the latest BLHeli_32 firmware, which is still on Beta (you have to flash through custom firmware). Bidirectional DShot sends the ESC telemetry data through the same ESC signal wire as DShot, so there is no additional wiring and hardware required.

How to Enable RPM Filter and Bidirectional DSHOT

Coming soon, just waiting for both Betaflight and BLHeli_32 to become more stable, setup will be easier too.

7 thoughts on “What’s RPM Filter and Bidirectional DShot

  1. Kyle J Minchokovich

    Could RPM filter work on a hexacopter (6 motors)? I have an older rotorx raiju that I would like to update with new motors and esc’s. Its using a omnibus f4 FC. Thanks for all the great insight you give.

  2. Ken

    Will the new bi-directional protocol enable betaflight OSD to report “Mah consumed” without a current sensor on the 4in1? For example, with the Bardwell blHeli-32 4in1?

  3. bambam

    Hey Oscar, I love love love your stuff. I used your rates for ages, until eventually changing them to suit my liking. Is there any way you could add dates to your articles? Or else tell me where they are if they’re there already because I can’t find one and it makes it hard to reason about what I should and shouldn’t do.

    Thank you for all your help!


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