How to install and set-up Betaflight 4.1.1 for use with BL Heli_S RPM filtering

Before you flash Betaflight 4.1 do a ‘dump all’ for your current version of Betaflight. This way, if something goes wrong, you can always go back to what you know already works. 

In other sections of this guide we will be plugging in a lipo battery. It is a good idea to run something like a fan over your quad to keep the VTX and stack cool.

  • Connect to Betaflight
  • Go to the CLI tab and type dump all
  • Click option near the bottom right – save to file. Save this somewhere you can find it again. If you ever need to reflash back to your old setup, you just paste the text from the dump all file (it will just be a .txt file like notepad uses) and all your old settings will be restored. 

Now that you have a backup, let’s install betaflight 4.1.1

(you also need to make sure you have Betaflight Config 10.6.0 so you can set up VTX tables. There is a link to this in the resources section of this guide)

  • Enter the CLI again and type BL. Or go to the main config tab and hit the bootloader option.

(For some FC’s this won’t work and you will need to either press and hold the boot button on your FC while plugging in the lipo, or manually short the boot pins).

  • This should force your FC into DFU mode. ‘DFU’ should appear in the place where your com ports usually display. Top right corner.
  • Click the Firmware Flasher tab on the left. 

You need to know the right target to flash. You can find this at the top of the .txt file we saved earlier doing the ‘dump all’. i.e OmnibusF4SD.

  • Select the legacy version of your firmware i.e OmnibusF4SD legacy. 
  • Make sure full chip erase is enabled. Leave everything else. 
  • Click Load Firmware Online down the bottom right. 
  • Wait until it finishes downloading, then hit Flash firmware. 
  • Wait until this finishes. You should be able to connect to betaflight 4.1.1 now. If you cannot, close Betaflight, unplug the USB, replug and try connecting again. 

Now we can configure RPM filtering in Betaflight 4.1.1

Config tab:

  • Enable the bi-directional dshot option. 
  • Set motor poles (14 for most 5” motors, my toothpick mamba 1103 were 12 though. Most micro motors seem to be 12)
  • Set dshot 300 4k/4k if you have an f4 FC. You can run 8k/8k dshot 600 on an f7 – but check cpu load. If it’s around 28-35% on 8k/8k 600, drop it back down to 4k/4k 300. (Type tasks in the cli to see CPU load percentage. You need to spin the motors first, then go into the cli and type tasks, hit enter, ignore the first result and type tasks again, hit enter.)

Save and reboot

CLI settings:

  • Type:  set dshot_burst = OFF then hit enter then type save and enter again
  • Type:  set scheduler_optimize_rate = ON then hit enter then type save and enter again (these should be turned on by default after turning on birectional dshot in the config tab.)

Check the motors arm after each change.

  • Unplug the usb. Plug in a lipo, then plug in usb and connect to Betaflight ( it is important to do it in this order. Leave usb plugged into the fc and remove from the computer end – that way you minimise the risk of a short when plugging in the usb to a live FC.)

Motors Tab:

  • Props off, check ‘I understand the risks.’ Arm motors. 
  • Look for the red line – When you spin the motors, you should see the RPM data and 0 error rate. Success! RPM filtering is enabled and working on your quad. 
  • If you see an error rate above 0, STOP!. Something is wrong somewhere and you risk a flyaway.

Unplug lipo.

Check exact error rate in the CLI:

  • Type Tasks – Look for the gyro/pid loop line – the value should be close to the dshot number being used – i.e 4k/4k is represented as 4000 in this line. 
  • You want an error rate of zero-under 1% – so 4001, 3996, 4012 etc etc. If this error rate is outside of the 1% range, DO NOT TRY TO FLY. RPM filtering might not be properly supported on your esc’s. 

You are now ready to go with RPM filtering. Below is a basic section on tuning. It is worth flying as is, then changing to these settings if things don’t feel right. 

Save a dump all to give yourself a backup. Test hover and check motor temps – go for a 30 second flight, check motor temps. Hot motors will be either a PID or filter issue, but probably more likely to be filters. 

If your motors come down cool, you can slide the filter sliders to the right and reduce the other filters. We want rpm filters to be doing most of the work. The more you can reduce the traditional filters, the better your quad is going to feel in the air. 

TUNING RPM FILTERS 4.1.1

Last thing to do is set up a couple of basic features – mainly in the filters tab and TPA

PID tuning – Filters Tab

  • Make sure Gyro RPM filter is turned on:

Set values to 3 and 100.

  • Look for the dynamic notch and set it up like this:

Low

0

250

100

TPA 

  • Set to .65 and 1550. Default is .65 and 1250. A higher TPA is better for handling high throttle oscillations – i think stock is too low in bf 4.1.1, so running 1500-1550 should feel a lot better. Leave it stock if you want to see how 1250 feels. 

Final thoughts

  • Fly with everything else on default – then adjust sliders after each flight on the filters tab and the PID tuning tab. It is easier to reduce filters on a clean/new build than an old/noisy build. Two notches up is about the max on older/noisy builds on the filters tab. 
  • You may need to play with your P and D levels if your motors are coming down hot. 

Check out the tuning notes in the GitHub link below – you can adjust the dynamic notch if the low,0,250,100 setting didn’t work. It is worth reading this entire write up.

Resources

Betaflight tuning notes:

https://github.com/betaflight/betaflight/wiki/Bidirectional-DSHOT-and-RPM-Filter

Betaflight Config 10.6.0:

https://github.com/betaflight/betaflight-configurator/releases/tag/10.6.0

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