Cannot connect RaspPi to Pixhawk Cube using battery power

Hey guys,

I’m trying to setup a drone to fly using APsync with the Raspberry Pi 4 (4G LTE capability). I have been able to get the mission planner to remotely connect to the drone while the Pi is powered remotely. However, as soon as I switch to drone power via 5V BEC the mission planner will just say “Mavlink Connecting” for a while and the fail to connect (not a timeout error).
The drone power is connected to the Pi via soldered pins on the bottom of the Pi, below the USB-C port. Other functions of the 4G system work using the drone power, including connection to the network and video streaming. The only part that has an issue when switching to drone power is the connection to mission planner itself.
Some things that I am thinking about:

  1. The BEC doesn’t provide steady power
  2. The power is somehow not reaching the pins of the Pi that have connection to the Pixhawk (5V, GND, TX, RX)
  3. I have heard that potentially using the pins on the Pi bypasses some safety measures, maybe it may also not be a reliable power source?

This connection issue happens even when the drone is not running and we have 2 6s 25000 mAh batteries that shouldn’t have any problems supplying necessary current.

Thanks!

Get a multimeter and check the BEC is actually supplying 5V. Some BECs supply 4.8V or less under load.

Also, try connecting the BEC power to the power pins on the GPIO header.

You don’t need the 5V line connected. That complicates the power flows.

Thanks for the reply!

I have confirmed the connection will also work powering through the usb-c port from a battery pack.

I have also tested the voltage and it appears to be steady at 5.04V. I have noticed that the raspberry pi red and green lights do not stay on while powering through the TP pins, which may be connected to the issue.

In regards to the GPIO pins I think the Pi 4 I have needs special equipment to input power through those pins.

No special equipment. Any correctly-rated BEC (5-5.1V, >3A) will work. Just connect 5V and GND to the appropriate pins: https://www.raspberrypi-spy.co.uk/2012/06/simple-guide-to-the-rpi-gpio-header-and-pins/

Otherwise, there’s pre-built power supplies such as the Pi-Connect: https://www.rpanion.com/product/pi-connect-lite/