Failsafe due to low battery voltage

Some intro. first. I am brand new with drones and electric motors. For many decades I have flown nitro and gasoline planes (0.35 to 110cc) and helicopters (450 to 900) without autopilots; only gyros for the flybarless heli heads.

The frame kit is a X500 with the following components.

  • Matek H743-Slim V3 FC
  • Matek AP_PERIPH GNSS M10-L4-3100 (GPS+Compass+Barometer)
  • mRo Sik Telem. radio v2
  • 4S2P 5600 mAh lipo
  • T-Motor F35A 32bits 3-6S ESC
  • iFlight 4pcs XING 2806.5 1800KV
  • HQProp 4pcs HQ Macroquad Prop 9X5X3 Tri-Blade Propeller 9 inch CW/CCW

After going through Arducopter’s “First time Setup” and “First flight and tuning” multiple times as I am familiar with helis gravity is ******* (lol) as they do not have wings do glide.

I believe the FC, GPS, Comp. and Bar are operating properly as I had no-propellers testing RC, telemetry, motors, failsafes etc. I put on the props and brought it a low hover for a few seconds looking very, very stable. Then I tried little longer and it went to failsafe with “Battery low voltage” and engaged RTL which worked perfectly, gained a few feet of altitude and then came to a very soft landing at the same take-off spot; failsafe is working!!!

I matched the PWM (min/max) from the RC Calibration to the BLHeli32 configuration (1003 - 1996) for all the ESCs.

The questions I have are:

  1. For the configuration (see above) should I decrease the BATT_CRT_VOLT (14), BATT_LOW_VOLT (14.8)?
  2. Did the combination of the motors/props is wrong for this X-quad size?
  3. Do you match the throttle PWM of the RC with the ESC?
  4. Using Dshot600 and I can not run the calibarion procedure for these ESCs, yes?
  5. I setup the MOT_SPIN_ARM 0.04 and MOT_SPIN_MIN 0.07 but I do not get these speeds during arming/spin-up. Props rotate almost twice as fast from these values.
  6. Anything else I should check?

I have attached the graph from that short flight.

I tried to upload the log file which is only 1.5 MB but got an error that cannot upload anything larger than 3.3MB…

Upload the .bin log to a fileshare site like dropbox or onedrive, then share the link to it.
If you connected to MissionPlanner and used Initial Parameters to set the battery failsafe voltages then leave them as they are.
For 4S you should have these:

If you feel the failsafe kicked in too early then check and recalibrate the voltage sensor at the minimum expected voltage (BATT_AMP_PERVLT) but the .bin log file will tell us more.

If you are using DSHOT (MOT_PWM_TYPE,6 for example) then you should have
and no need to calibrate ESCs.

With the BLHELI ESCs connect with the BLHELI32 Suite using passthrough and set these even if you dont use DSHOT
Low RPM Power Protect = OFF
Low Voltage Protection = OFF (rely on the flight controller battery settings)
Temperature Protection = 90
Motor Timing = Auto

First of all thank you Shawn for taking the time to help me!

You can access the bin log (zipped) 2023-03-17

I just got back and I am looking at the parameters.

I followed the instructions on measuring/verifying battery Voltage with 2 multi-meters (cheap one and FLUKE 322) and both matched the HUD displayed Voltage within 0.02 Volts. Unfortunately, the FLUKE only measure AC currents and the cheap one is below 10 amps. I think is about time to look for a mid-level dissent multi-meter maybe analyzer.

The great info. I got from the video was to reverse and switch CW/CCW props to produce downward thrust for testing because the real one is not good for my nerves lol !!!

btw what is your opinion for the choice of motors and props for the X500 frame?
Vendor recommend 2212 900KV motors an 2 blade 1045 props. I thought a 2806.5 1800 KV with a tri-blade 9x5 prop will achieve similar thrust or I am very, very wrong :slight_smile:

More information tomorrow.
Many thanks!

BLHeli New setup:


So I reversed the props and run some tests running the motors with down-thrust. At always failed at about half throttle with “Low Battery” Failsafe.

This taken a couple of minutes after the Failsafe triggered and disarmed.
65.6 deg is the capacitor and points 2 and 3 are ESCs.

Below FLIR with half throttle just after disarming.

At this point all tests are halted. I believe something is very wrong with my setup. I have ordered 4 2213 motors and 1045 props and I will re-test then.

Any thoughts?

From the previous tests the log (bin) files:
2 3-19-2023 2-51-56

3 3-19-2023 2-56-48

Motors at 80 degrees is bit of a problem.
1800kv motors wont be much good for a copter this size.

I thought so about the temperatures. Yah, I had a feeling I did some bad choices with motors and props. Tomorrow I should receive a set of 4pcs Emax Mt2213 935kv Brushless Motor 2CW 2CCW with Original 1045 Propeller for DJI F450 F550 Quadcopter Hexcopter Octo Copter. I hope for the low price of this motors package, they will work at least ok. I have searched for 2212/16 motors and it seems they are not that many choices of a reasonable price…

Also, this is my very 1st drone, 1st FC, 1st ESC, 1st Arducopter/pilot etc. :scream: I am sure I had made some bad parameter entries so I decided to start with a clean slate, and I mean re-flash the FC with a full erase. It’s surprising with the knowledge I have gain (and notes) how fast I configured Arducopter! This resolved some weird issues I had before, like even setting up MOT_SPIN_ARM 0.05 the motors will spin close to 0.15!!! Not anymore!

Now I am looking if my ESC/PCU can be setup for Bi-directional Dshot, I have loaded the bl version of the firmware (arducopter_with_bl.hex)) already. It will be great to get some RPM, V, Amp, temp. data out of the motors.

Anyway, thank you again for the comments and taking the time.

You can just do a “reset to defaults” instead. Also you should flash the bi-directional DSHOT version of the firmware for your flight controller.
It will have “BDSHOT” in the name when you go into the firmware section of MissionPlanner

Then start with:

  1. mandatory calibrations
  2. set up the voltage and current monitoring
  3. Initial Parameters, also select suggested settings (accept everything it offers)
  4. set any other requirements, like
    PILOT_THR_BHV,7 if you have a spring-centered throttle
    SERVO_BLH_POLES,14 ← check this matches your motors

EDIT: also set SERVO_BLH_BDMASK,3840 to suit your motor connections

And set these:
INS_HNTCH_ENABLE,1 ← set this then refresh params to see the rest

There are some reboots required in amongst that - like after setting the battery monitor type.

Do a hover test flight and some gentle pitch/roll movements, then post that .bin log

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Hi Shawn,

Sorry for the delayed response but finally installed the new motors and was waiting for less windy day as it is been very windy here so the best I could do was a 2 ft hover in the garage (WARNING: anyone reading this DO NOT do that unless your heli/drone feels and looks stable; also I am flying RC helis for 15 years; still not recommended :smiley: ). Anyway, I had a few short hovers and the motors are barely warm. ESC and capacitor/PDU cold.

I finally managed to calibrate the voltage by extrapolating the actual and HUD readings (BATT_VOLT_MULT). I am working on the Amp. output as I do not have yet a reliable Amp. meter. Until now no “Low Battery Failsafe” but a full outdoor hover is still pending.

I still working getting any readings from the ESCs. Matek support is more gear towards experience electronic users, which I am not, so I gave up on any further help from them. I am working to interpolate the mappings between the FC and PDU to pass to Ardupilot.

I have applied the following:
PILOT_THR_BHV,0 Heli radio JR 12X
SERVO_BLH_POLES,14 ← waiting from seller as was no infromation on the packaging.

SERVO_BLH_BDMASK ← Do not know yet.

INS_ACCEL_FILTER,20 ← Drone has zero visible vibrations. Still lower value to 10?

Holding back on INS_HNTCH_ENABLE until I short out the ESC telemetry.


I will fully charge all the batteries tonight and tomorrow I will take another hover and post the bin logs.


Today’s outdoor hover logs:

2023-03-24 16-39-56.bin

2023-03-24 16-38-20.bin