Compensation of Voltage Sag Fluctuation, Causing Non-Linear Behavior

ArduCopter
1

Hi everyone,

I’m experiencing an issue with my drone where the voltage compensation, which should ideally provide a linear response, is fluctuating and behaving inconsistently. This fluctuation seems to be correlated with voltage sag under load.

Here’s what I’ve checked so far:

Battery Setup:

  • MOT_BAT_VOLT_MAX and MOT_BAT_VOLT_MIN are configured correctly based on my battery specifications:
    • Max: 6S = 6x4.2V = 25.2V
    • Min: 6S = 6x3.3V = 19.8V

Despite this, the voltage compensation doesn’t seem to follow the linear thrust curve it’s supposed to, especially during high throttle. The behavior seems worse under sudden throttle changes, likely due to voltage sag. Additionally, due to the fluctuation in the voltage curve, the low battery failsafe is triggering much earlier than it should. Instead of triggering at 19.8V as configured, it’s being triggered at a higher voltage.

Any guidance or insights would be greatly appreciated!

This is the Voltage sag and Voltage compensated Curve for Radiolink power module, where this issue is arising:

Screenshot 2025-01-17 at 4.07.55 PM
Screenshot 2025-01-17 at 4.07.55 PM2088×1252 244 KB

This is the Voltage sag and Voltage compensated Curve for Generic power module (not fluctuating):

Screenshot 2025-01-17 at 4.06.27 PM
Screenshot 2025-01-17 at 4.06.27 PM2094×1300 242 KB

2

Your graphs look like the battery is quite poor, or there is more current draw than it can handle.

These are the settings you should have for 6S LiPo

BATT_FS_CRT_ACT,1
BATT_FS_LOW_ACT,2
BATT_ARM_VOLT,22.10
BATT_CRT_VOLT,21.00
BATT_LOW_VOLT,21.60
MOT_BAT_VOLT_MAX,25.20
MOT_BAT_VOLT_MIN,19.80

Dont be tempted to change these voltage levels, they are quite “tried and true”.

If you have a low C battery then you can set this to use the sag-compensated voltage:
BATT_FS_VOLTSRC,1
and to change the overall sensitivity:
BATT_LOW_TIMER
which you would normally set smaller, like 5, rather than longer, to ensure there is enough battery left to complete an RTL especially for long flights.

Any other situation means your battery is poorer than you expected. Check if there are any connectors getting hot, if so replace them.

1 Like
3

And get rid of anything from Radiolink. They are bad actors with respect to the Ardupilot’s GPLv3 license.

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5

This is double posted and in the wrong place in both instances. Suggest you delete both and create a new post.

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