For a little while now, 6s has been the new standard for FPV drones, but some still own quads with 4s motors and 4s batteries. If your quad has a 6s capable stack (ESC flight controller combo), you can program, in betaflight, a smart motor output limit. This would allow you to run 6s on 4s motors without burning them, and to run 4s without having to change the settings manually in betaflight everytime you change battery voltage. If you plan on running only 6s, 6s motors will be better, but still good to know for when 8s becomes more popular.
Motors don’t have an actual voltage limit, the arbitrary limits from the specs list are based on max RPMs, so by limiting the motors RPMs, you can run any battery through it.
A motor limit is the better method of achieving this. Using a throttle limit can work too, but when doing flips and rolls, the motors aren’t limited. With a motor limit, the RPMs are limited at all times, which keeps your motors from overspinning.
First, you’ll have to calculate the right motor output percentage for your motors. You’ll take the nominal 6s motor kv for your drone size (for a 5 inch freestyle 1750kv) and divide it by your motor kv (2550kv for example). 1750/2550 x 100 ≃ 69%. For your 6s profile you’ll have to set the motor limit at 69%.
To enable this motor limit you’ll need to connect your drone to betaflight.Go to the Power & Battery tab, and make sure your maximum cell voltage is at 4.35V. This will make sure that the correct profile is applied even if you are using LIHV batteries.
Then go to the PID Tuning tab, you will need to copy your current pid tune profile to all the other slots. Press on Copy Profile and apply to the other slots.
The head to the CLI tab, there enter or copy the following text:
profile 0
set auto_profile_cell_count = 4
profile 1
set auto_profile_cell_count = 6
set motor_output_limit = 69
profile 2
set auto_profile_cell_count = -1
save
To verify that the programming was successful, remove your props, and go to the PID tuning tab. Plug in a 4s and then a 6s battery, you should see the profile change by itself at the top left.
You’re now ready to use all your batteries on 4s motors. You can do this for all drones, as long as the flight stack supports the higher battery voltage. Keep in mind that it is better to use the appropriate motors for your battery, but this can help out if you don’t want to change the motors right away. For more questions please contact me by email at info@epicfpv.ca