How to Setup Betaflight RPM Filter

Setting up RPM filter has become super simple since Betaflight 4.1, the hardest part is probably updating your FC and ESC :) If you find the official guide too much to swallow, you might find this quick tutorial useful.

RPM filter is designed to reduce motor noise and it makes your quad fly better. According to many pilots, RPM filter is by far the best filtering in Betaflight. You should definitely give it a try if you haven’t already.

Looking for new ESC’s that support RPM filter?


What is RPM filter?

Notch filter is very effective for killing noise, there is less signal delay than a low pass filter for the same amount of attenuation. You can read more about filters in our Betaflight Filter 101 course.

The challenge comes from tracking the peak frequency of the noise. Dynamic filter does this pretty well, but it only tracks one frequency. Motors in a drone can all spin at different RPM (rotation per minute), hence making noise at different frequencies.

RPM filter is basically a collection of notch filters, precisely targeting the noise frequency and its harmonics from the motors, by getting motor RPM from ESC through bidirectional DShot.


Flash Latest BLHeli Firmware

REMOVE ALL PROPELLERS BEFORE WE BEGIN

Update your BLHeli_32 ESC to version 32.7 or newer in order to use “bidirectional DShot”, which is a necessary feature for RPM filter. (Instructions on How to Update BLHeli_32)

You can also do RPM filters on BLHeli_S ESC, you just need to flash a special firmware. This tutorial explains how to setup RPM filter on BLHeli_S ESC.


How to Setup RPM Filter in Betaflight

Update your FC to Betaflight 4.1 or newer (How to flash Betaflight, after updating Betaflight, don’t forget to setup VTXtables if it uses SmartAudio, otherwise your VTX might not work properly)

Use 4KHz looptime.

With faster looptime (i.e.. 8K) you might get jitters, 4K is a safer option and most people probably won’t notice the difference anyway.

For 4K looptime, DShot300 ESC Protocol is fast enough. You only have to use DShot600 if you are using 8K looptime.

For BLHeli_S Users, use different config based on the ESC processor

  • Use 4K looptime and DShot300 if you have “H” type ESCs (BB2)
  • Use 2K looptime and DShot150 if you have “L” type ESCs (BB1)

Enable “Bidirectional DShot“, and set Motor poles.

Simply count how many magnets you have in the motor bell, that’s the number you have to enter in Motor Poles. If you put the wrong number in, filtering is not going to work properly (doesn’t report the correct RPM). As a general guideline:

  • 14 poles in 22XX, 23XX, 24XX motors
  • 12 poles in 08XX, 11XX, 12XX, 13XX, 14XX, 16XX motors

It’s best if you count it yourself to avoid any surprises.

Now go to the motors tab, on top of the sliders, you might see DShot Error at “E:100%”.

As soon as you plug in the battery, they should all go to 0%. If they don’t, something is wrong. You might want to use a slower looptime if you are running 8K/8K.

You can now spin the motors up with the sliders (apply just a little throttle), to make sure they work properly.

Now go to the PID tuning page, under Filter Setting, enable “Gyro RPM Filter“. Just leave the two settings at default.

By default, RPM filter is set to target 3 harmonics for each motor (4 motors), on each axis (pitch, roll, yaw), so it gives you a total of 36 notch filters!

After your flight controller reboots, go to the CLI and enter

tasks

Check if the value of “Gyro/PID rate/hz” is close to your looptime. For example, For 4K/4K it should read around 4000. It doesn’t have to be exactly the same, but the difference should be less than 1%, otherwise you should lower looptime until it is. (as recommended by Betaflight devs)

Now go out and fly your quad, it should feel pretty good. But we are not quite done yet, you can still tweak the filtering settings to get more performance out of it.


Removing Default Filtering

Simply adding RPM filters will certainly make your quad fly smoother and the motors cooler, but we should take advantage of the excellent noise rejection from RPM filter, and try to minimize the default filtering delay.

This is actually the part that makes your quad fly so darn good without propwash :)

Under Dynamic Notch Filter:

  • Leave Filter Range at Medium, but if motors are cool you can try changing it to LOW
  • Change Width Percent to 0 (setting this to zero will remove one of the two dynamic filters and decrease latency)
  • Q factor to 200 or even 250 – for a narrower filter
  • Set Min frequency to 90 as there is less high frequency noise now thanks to RPM filter, and we want to focus on lower frequency

Test your quad again, I suggest doing this with used propellers as it will give you more objective results.

If the motors are cool, it probably means you can reduce filtering  further. But this time we will use the two sliders on the top of the filter tab – Gyro Filter Multiplier and D term filter multiplier.

You don’t have to change any of the check-boxes or numbers under the sliders. These adjust themselves as you move the sliders left and right.

Try dragging both of the sliders to the right for less filtering, just a tiny bit every time you test fly the quad. Check motor temperature and assess if you can reduce filtering further. Note that even if the motors don’t get hot, without enough filtering, your quad can actually perform worse, so keep that in mind, motor temperature is not the only thing!

To get more tuning tips, make sure to read the Betaflight official guide.

Edit History

  • May 2019 – RPM Introduction published
  • Jan 2020 – Setup tutorial added

29 thoughts on “How to Setup Betaflight RPM Filter

  1. Thomas

    Hey, I just switched to the Maverick 16.73 ESC FW, now I could Setup my RPM filter, all is working well and first flight will be tomorrow!

    Thx Oscar for your awesome work with your blog!

    Reply
  2. Thomas

    Hi,
    what could be the reason that Betaflight 4.2 shows the E:100 in red at Motor tab?
    I have a BB2 ESC (Aikon SEFM 30A 2-4S)
    My FC is a Furious FPV Fortini F4 OSD Rev3,
    I used 8k/4K and Dshot300.
    I followed all the instructions, but something seems to be wrong.

    What could be the reason?

    Greets Thomas

    Reply
  3. Tim Howitz

    Hi Oscar,

    I’m running betaflight 4.2 and I don’t seem to have the dynamic notch filter range option,, does this matter? Do I have to change any other filter settings? I do now have a dynamic notch max hz, the default is 600, should I change this?

    Many thanks,

    TIm

    Reply
  4. Luis Leston

    Thanks for this wonderful material. After following it I was able to fine tune my quad. No prop-wash at all!

    Reply
  5. Sebastien

    Oscar i have recently come across a strange problem that I cant seem to solve, my drone can take off and move around at a reasonable pace but the second i try to do a flip or go anywhere near a 90 degree angle the quad freaks out and goes full throttle in random directions, i have swapped out a flight controller as i had a spare one and that isn’t the problem, I am not really sure what to do!! I had also flown this quad 3-4 times properly (with flips and tricks) before this happened and i haven’t changed any betaflight settings since then.
    Would appreciate advice from anyone.

    Reply
  6. Carlos

    My props all of a sudden are breaking and im getting vibrations.. i upgraded from 1105 to 1204 motors on a beta85x and this began to happen.. im suspecting is the filtering.. any ideas?

    Reply
  7. Frank

    Hi Oscar,
    My quad is HGLRC Parrot132 4s version. Yesterday I update my flight ctrl from 4.11 to 4.1.3, and I follow instructions to update ESCs to support bidirectional Dshot and use free JazzMaverick’s P_H_10_48_REV16_79 firmware. Everything was good to moment when I want to turn on bi-directional Dshot protocols and plug my battery I noticed E – 100% on motors tab. But when I turn off bi-directional Dshot, motors tab back to normal again. I don’t know what should I do to fix this problem.
    I set 4K4K looptime, DShot300 ESC Protocol. Help me PLZ,

    Reply
  8. Arnold De Groot

    Help?
    Now go to the PID tuning page, under Filter Setting, enable “Gyro RPM Filter“. Just leave the two settings at default.
    There is no “Gyro RPM Filter” setting under Filter setting.
    Perhaps this was the case in BF4.1.0 and now in BF4.1.1 separated into 3 other filters ?

    Reply
  9. Fabrice

    Hello Oscar,
    always on top the documentation that can be read on your site.

    About the 4KHz gyroscopic sampling rate and 4KHz loop time,
    is it not reliable to put 8K / 8K even in Dshot 600 if my FC allows me.

    It’s an F7

    Reply
    1. Oscar Post author

      BF documentation seems to suggest 4K is more reliable than 8K mostly. But check CLI status anyway as suggested in this post.

      Reply
  10. Bastian

    Does anyone know how the bidirectional DShot protocol works on a communication level? I’m trying to run a motor/ESC from an ESP32 and I got DShot to work. Now I have to get the motor RPM. I don’t necessarily need bidirectional DShot (if I can get the RPM over Serial that would be ok too), but it would be nice.
    What I mean is in which form is it communicated? Is there a way to get to that information? I’ve been browsing on the spec all day long and it seems like I have to send some number within the 32-35 range via DShot to get the RPM back. But there’s very little other information. Sadly, I don’t have an oscilloscope or logic analyzer so everything I could do is write some Arduino code to read the pin and so on.

    Reply
  11. Steven Potter

    Hello Oscar,

    Any new news about Bidirectional RPM filtering on the CLracing F7 Dual gyro? M4 solder to what? LED? or what’s the what?

    HobbyWing ESC which has BAT next to 5v and then GRND on the io jack battery voltage? Where does this go??
    THE F7 has a telemetry wire on the io jack where does this go??

    Thank you for your time,

    Steven

    Reply
  12. 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.

    Reply
  13. 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?

    Reply
  14. 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!

    Reply

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