Help on electronics!

Hi there 

I am in the Johannesburg area and it s the first time I am posting on this forum, please be patient for my terrible english and my noob questions

I am building an octo, using for the first time the APM 2.5, I am reading/studying a lot but I really need some help.

Basically the octo will be powered by two PDBs, one powering only escs and motors (6s) and the other powering the fpv,vtx,flight rx etc.(3s or 4s) The two PDB have a common ground. I am thinking to power the APM from a dedicated battery and BEC.

- I am using the Platinum Pro 30A opto ESCs which don't have an on board BEC, so I am planning to cut off the red cable, send only the white cable to the matching output on the APM and connect the black cable to the common ground of the PDBs. Would this work correctly?

- I will use a Futaba T8J linked to a Delta 8 frSky rx. If I put the jumper on the rx signal pin 3 and 4 and a jumper on the APM inputs signal 2 and 3 will I be able to connect the rx to the APM by the only signal wire on CH 1as the APM will use the PPM streaming? Will I need to update to the latest 

ArduPPM_v2.3.16_ATMega32U2.hex  or is there a way to check if it is already loaded with the APM firmware?

- I found this sensor at I would like to put it in the main PDB (ESCs and MOTORs) does someone know if it'd work with the APM? Where would I connect the three pins?

- Lastly where do you guys buy batteries in big quantities? They cost a fortune!!!

Sorry for the many/long questions, any help or reference is highly appreciated, thanks a lot



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  • Moderator

    - No need to cut the red wire on the opto ESC's as there should be no voltage on that anyway. Common ground should be OK but I once had a ground loop problem causing a blown APM so caution should be exercised (and keep things simple.)

    - no idea on the PPM stuff, sorry.

    - AFAIK there is no support for a hall effect sensor, not sure why you would want that anyway?

    - Hobbyking for the batteries but shipping can be a killer

    • Hi Graham

      so you reckon that if I cut the red wire off it shouldn't be a problem any way ( i already did in a couple of escs)

      I did hear about the ground loop problem, do you know what to do to avoid it? that s why I thought a "clever" idea would be to connect only the signal wire to the APM and power it from a dedicated battery,,,

      The idea of the sensor was for monitoring the batteries from the esc's  pdb, in one of the forum they suggested this one that seems to work, the one I found seems to be the same without the board. 

      Thanks for your help


      Allegro ACS758 Current Sensor Module 50A/100A/150A/200A by BBTech on Tindie
      Allegro ACS758 Current Sensor Module
  • Hi Fransco,

    Welcome, here is a link that you really need to study....

    And after that, try to hook up with one of the many JHB drone guys.

    A new APM 2.5 will only have the bootloader, you need to pick what firmware you want to load.

    Unfortunately I'm in Cape Town :-)

    • Hi Gustav

      thanks for your reply, I m reading those pages till my eyes are sore but still confused about the issues in my previous post.

      I am desperatly seeking for a local "guru" willing to share his knowledge, but doesn't seem an easy task!!!

       I ll keep  on looking



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