Even if your motors KV are for 4S LiPo (for example 2208 2500KV), you can still put a 6S LiPo on your quad. This is a new feature in Betaflight that auto adjust motor output to compensate for the voltage difference.
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Make sure your hardware support 6S voltage before trying this! Otherwise you could fry your ESC and FC. (as well as VTX and other components if you power them from LiPo)
You will probably lose some efficiency and get shorter flight time compared to running lower KV motors.
The main risk is when you crash and the motors are obstructed, ESC’s and motors are more likely to burn out.
It Feels Differently
As explained in my motor buyer’s guide, the KV of a motor affects torque constant. A higher KV motor would require more current to generate the same amount of torque as a lower KV motor.
For example, indeed you could use a 2400KV motors (for 5″ on 4S) and run 6S on them. If you limit maximum throttle in the flight controller, it will work and not burn out. Besides the lower efficiency, it would also feel very differently when it comes to handling than using a 1800KV motor that’s designed for 5″ and 6S.
Using Betaflight for Automatic Profile Switching
Go to PID Tuning tab, and select PID Profile 1.
After navigating to the PID tuning tab, scroll all the way down to the bottom of the interface, find Cell count for auto profile switching.
Under Motor Output Limit, set the Scale Factor to 100% and Cell Count to 4. Press the Save button.
This is the PID Profile for your 4S battery.
Then click on the ‘Copy Profile’ option and copied all values from Profile 1 to Profile 2, which essentially made the two profiles identical.
Now select PID Profile 2.
Under Motor Output Limit, set the Scale Factor to 66% and Cell Count to 6. Press the Save button.
This is the PID Profile for your 6S battery.
Now when you plug in your 6S battery, Betaflight will automatically scale motor output down to 66%. You can think of it as “Betaflight automatically reducing the motor KV for you”, although it doesn’t really quite work that way.
Note that Betaflight would select the PID profile based on the battery you plug in, so if you make changes to PID or any other settings in the profile, you might want to copy them across profile 1 and 2.
Using 4S battery on 6S Drone?
If you have a 6S quad, you can’t scale up motor output to 150% and hope it would performance the same on 4S LiPo. You can only reduce motor output, you can’t increase it.
When scaling down motor output in Betaflight, we are basically putting a limit on the output of the ESC, more specifically, the signal duty cycle to the FET’s (how long the pulses stays high).
Alternative Method – CLI Commands
Entering these CLI commands basically achieve the same thing as what I have shown you above.
set auto_profile_cell_count = 4
set motor_output_limit = 67
set auto_profile_cell_count = 6set auto_profile_cell_count = 6