Flipsky 75100 pro V2.0 Vesc with VX3 pro controller battery voltage readings incorrect

Rocket · October 5, 2025, 11:24am

Hi Guys

Assume I’m not the first person to have these issues but can’t find any discussion topics on this.

Issue 1
When reading the voltage of my fully charged 11S3P from my Vesc through Vesc tool in the real time data display it show 45.2Volts and level at 94% when my multimeter and another battery checker I trust both read the battery at 45.9 volts and 100%. My VX3 pro also reads down from full (about 94%) on the bar across the top of the screen.

Issue 2
Regardless of what settings I put in the voltage tab of the motor configuration for the cutoffs (lower volts) the VX3 pro controller gives me the low voltage red warning when my battery is at 38.3-37.8 Volts which is nowhere near the 34-35 volts that I know I can run the battery down to (the figures I entered as my cut outs in voltage tab). Does this mean that the controller has some sort maths calculation in it that is separate to the values we enter into the voltage tab?
If so, is there a way to get the warning to correspond to the correct low voltage settings?

Jan12 · October 5, 2025, 11:35am

1
I think that is common, I would not worry about it.
The VX3 is probably reporting the voltage readings of the VESC

2
The controller knows nothing about the values you put into VESC tool, as far as I know.
As far as I remember, you just enter the number of cells into the remote config and there is no way to adjust the htreshold value.

ZedMan · October 6, 2025, 1:45am

I run 14s and the Flipsky remote is useless, with the battery bar at around 1 third for safe low voltage.

The problem with using a voltage limit in the ESC is voltage sag activating it and when it recovers, it is much higher and more battery could have been used.

Logging is the best way to sort out battery management, then the checked battery level when the voltage recovers.

I have a battery box at the front of my board with a battery checker on it that I can read while foiling which was a real educational experience to see the difference under load, and then to compare to the logs.

I don’t know how everyone else decides that the session is over due to reaching low battery, but I’ve tried different things from distance on my gps watch, stopping to try and read the Maytech remote, and previously at 8s with the warning on the Flipsky remote.

The battery checker display is the best for an under load reading with 5% a good limit.

I know not everyone can do this, and my next build probably won’t have it, but it is good for now and a learning experience for voltage readings across the system.

ludwig_bre · October 6, 2025, 6:54am

I also had this problem for a long time
That’s why I added a feature in my remote for that purpose now You need to tell the remote your type of battery (Manufacturer name) and the load you put on it on average
That way the battery discharge curve is matched to the voltage measured by Rx or VESC and any sag and non-linearity is compensated

More information here:

Kian · October 6, 2025, 7:40am

We noticed that our lab bench power supply is also some mV’s out of what the VESC is reporting.
The higher the voltage, the more it gets.
This is overt the BLE, UART and CAN messages.

At 60 volts the VESC is reporting 59.15 volt
At 20 volts the VESC is reporting 19.8 volt

Strongarm · October 6, 2025, 1:17pm

I’ve programmed a lot of VESCs now and they all seem inaccurate and variable with their voltage readings. I get a couple of percent difference in the calculated percentage.

My theory is that they will use a low accuracy resistors for the voltage divider to calculate the voltage.

It would be great if you could sort this out in vesc tool using a voltage calibration value, but I’ve looked and no such option exists.

Kian · October 6, 2025, 2:26pm

They have some code in the VESC firmware, but you will need to recompile it.


//The voltage dividing acquisition circuit on the Makerbase VESC motherboard is 56K and 2.12K resistors.

#ifndef VIN_R1 #define VIN_R1 56000.0 #endif #ifndef VIN_R2 #define VIN_R2 2150.0 #endif … … … // Input voltage #define GET_INPUT_VOLTAGE() ((V_REG / 4095.0) * (float)ADC_Value[ADC_IND_VIN_SENS] * ((VIN_R1 + VIN_R2) / VIN_R2))

See line #111 and after.

github.com

WeDo-ESC/bldc/blob/master/hwconf/makerbase/84_100_HP/hw_mksesc_84_100_hp.h

/*
	Copyright 2018 Benjamin Vedder	benjamin@vedder.se

	This file is part of the VESC firmware.

	The VESC firmware is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    The VESC firmware is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/
	
#ifndef HW_MKSESC_84_100_HP_H_

This file has been truncated. show original

ZedMan · October 7, 2025, 2:42am

Thanks for this. It definitely is a scaling issue based on:

“VESC voltage readings can be off by a few percent due to resistor-divider tolerances and ADC scaling, and you usually can’t calibrate that easily in VESC Tool.”

As @Kian has demonstrated.

I’ve been trying to get my voltage cutoff set for the desired battery percentage usage and something was off. I thought incorrectly that it related load from the ESC or battery sag.

But my battery sag is as bad as I thought, but also ESC readings are off, so they are a usable indicator but not for the exact values.