Power module and pixhawk


Hii Guys

   I have tried to produce an agriculture drone. I just completed all set-up configuration and I have performed the first flight attempt. however, the agricultural drone  could not take-off because the  voltage supplied by my batteries were not enough to produce the required RPM of the motor for take-off.

Frame :x8 octoquad

Motor : U8II 85 KW

ESC : Alpha 80 A HV

Propeller 29x9,5

Controler : Cube

Battery : 2 x 6S (serial )

       I used 6S 200A power module because I did not have a 12S power module. I know that I have to use HV version but I dont want to waste time while shipping. so, I connected the 6S power module to one of the batteries and then connected the power module in series to the other battery before connecting the batteries to the ESC. Is my circuit arrangement affecting the voltage produced by the batteries to drive the motor at the required RPM for take-off?

Best wishes…


Could you please share a flight log file via http://logs.px4.io? Please also make sure to use the latest version of the PX4 firmware.


Dear Meier

Thank you very your soonest reply but I can share you log file on Monday…

See you monday


Dear Meier:

     I try to share log file via https://logs.px4.io/  which  are *.BIN and *.LOG formats but continuosly I had gooten file format mistaken, would you pls tell me which format is possible...

Best Regars


hey @SmS,

Try uploading your log to a flight report on https://review.px4.io and share the link to the report.


I looked at your first post and just did a quick check out of what I understood. Here’s what I am wondering based on your first post.

  • Do you have two 6s power modules hooked up in series from each battery to get 12s at your ESC’s
  • Do you have one 6s power module that has two 6s batteries hooked up in series to act like one 12s battery
  • Do you have one 6s power module that has two 6s batteries hooked up in parallel to get 6s at your ESC’s?

I put the numbers you listed into a static thrust calculator (http://godolloairport.hu/calc/strc_eng/index.htm) with:
Prop Diameter = 29"
Pitch = 9.5"
Standard Propeller
CF = 1
No. of Blades = 2
Air temp = 68F
Air density = 1.2045

I got RPMs in 2 ways.

First, I assumed your ESCs are getting a full 12s potential difference:
–> (3.7v Nominal) * (12 cells) * (85kV) = 3552 RPM
This RPM outputs over 25 lbs of static thrust which would be 200+ lbs thrust on an octo.

Second, I assumed your ESCs are only getting 6s. In this case,
–> (3.7v Nominal) * (6 cells) * (85kV) = 1776RPM
This RPM outputs about 7 lbs of static thrust which would be just under 50 lbs of thrust on an octo.

These numbers are based off of nominal voltage, so they are conservative. More info on your power distribution wiring setup from batteries to ESCs would be helpful, as would the weight of your copter but by the sound of it, your ESCs aren’t getting the voltage.


Hiii Dear JrodJiggle

       Firstly Answers your questions.

         I'm using two 6S batteries and only one 6S Power module. The batteries are connected in series to ESC while the only 6S power module is connected to only one of the batteries. Gİven this arrangement, I would only be able read the voltage of one of the batteries on the HUD screen which approximately half the voltage of both batteries although 12S batteries voltage should be shown on the HUD screen. 

I tested the two motors attached to one arm of my Octoquadrotor on the test bench and all the test data such as thrust were quite good. if you wich to see the Excel file of the test data, I can send it to you.
I am using Alpha 80A HV ESC.

       I tried to upload log files several times but Unfortunately, I was not succesfull. The log files were not accepted by the server. Could you please tell me what file format to be upload?  Are *.BIN and *.LOG the correct file formats? Can you offer me other file sharing servers?

@SmS I use https://review.px4.io to review and host my flight logs, and use QGC to pull them from my SD through the FC via USB. Mine come out with a .ulg extension. I’m not sure on .LOG extensions, maybe someone else can chime in on that.


Dear Meier:

        Fistly sorry for my late reply, I couldn t share with you log file via https://logs.px4.io/ this web page because I got "Invalid file type " message when I tried, firstly do you know any converter software frim .BIN to .ULG   .  if you share me I will be very pleasure.

       Secondly I was upload we transfer Datalog, video and Electrical Connection diagram you can download below the link...

Datalog : https://we.tl/t-H8FuF8fzX4

Video : https://we.tl/t-WLwi9QrXKe

Connection Diagram : https://we.tl/t-glr2m35wFt

    Best Regards