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PixHawk and power distribution

Posted by Rich B on June 12, 2014 at 2:17pm

Hi,

I have a PixHawk and have some questions about the power configuration. There seems to be some confusion (as least for me) as to the best method and practices. I find most of the documentation and diagrams talks about APM, but hasn't been fully updated for the PixHawk environment yet.

 

I have the following equipment:

  • PixHawk
  • 3DR-Radio (900 MHz) connected to Telemetry1
  • MinimumOSD connected to Telemetry2. 5V only pads on both sides have been bridged so it runs on the 5V from the Telemetry1 port.
  • 3DR power module, for monitoring the 4S battery and to supply power to the PixHawk via the power connector.
  • 3DR ublox GPS and compass, on a GPS mast, connected to the GPS and I2C port.
    FrSky X8R RC receiver connected to the RCIN port.
  • LEDs on each arm of a FW-450, connected to the power buss of the FW 'chassis'.
  • Four DJI E300 ESCs, running four of the E300 2212/920KV motors
  • 5.8 GHz transmitter, running from the balance connector of the 4S battery.
  • FatShark pilotcam 700CCD camera

 

I thought I see some brownouts on the MinimumOSD (the screen would go blank sometimes as I turn on my RC transmitter), so I was going to use a 5v switching (Castle Creations) 10A BEC to power the RC Pins of the pixhawk, and then directly connect the 5V power and ground of the minimumOSD to the RC pins of the pixhawk (to get power) (or should I use the main-out pins?)  Would this be a good idea?

The input of the 5V BEC will connect to the power buss of the FW450, so it would have plenty of current input.  But I'm worried about a ground loop. Should I disconnect the ground wire at the output of the 5V BEC as it conects to the pixhawk? If I do this, wouldn't this mean that the current would come through the 3DR power module wires (are they heavy enough for this extra current)?

Also, I believe the DJI ESCs do not have BECs, so is there any reason to disconnect their ground wires from the connectors that connect to the main out connectors on the pixhawk, or can I leave them connected (as well as the center 'power' pins) on the signal input lines to the ESCs?

 

Thanks for any ideas about how to best configure this.

 

Rich

 

 

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Replies

  • Phill Simpson July 2, 2014 at 7:11am

    The doc for the 3DR power module say that it has a minimum amount of power available. Pixhawk, GPS and Reciever are safe to power from it. I've also added telemetry and it still works. The OSD may be sucking up too much power as you already suspect. I've added a 5v, 3 Amp 5v BEC and a 12v 3Amp BEC to power my accessories and it seems to work fine, but I don't route it through the PixHawk. I wouldn't use a 10 Amp BEC, if something goes wrong, 10 amps is a lot of power to shove through a problem circuit.

    • Rich B > Phill Simpson July 4, 2014 at 6:52am

      Phil,

      Thanks again for your reply. I'm using 5V only for my easyOSD telemetry card as I've already blown one up using a separate analog power supply input for it. So I think it's just safer to use only 5V power for it.

      I already had the 5V 10A BEC, so I'll just use it for now. If later I get a smaller one, perhaps I'll replace it, but for now, the 5V BEC can supply backup power to the PixHawk as well as power the minimumOSD.

  • Rich B June 16, 2014 at 6:44pm

    Anyone have any thoughts or input on this?

    Thanks!

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