PX4 Not responsive to any commands or data from QGC/Rpi

I am trying to set up a Raspberry Pi 4B connected to some ultrasound sensors and use that data in my Pixhawk 4. Before the christmas break, I had at least some communication both ways set-up. Now, however, I am running into a very annoying problem. As far as I know, it is unlikely any component suffered real physical damage, but nothing is impossible.

My Pixhawk will not take any commands from either QGC or the RPi. It still connects and I can request some data from the Pixhawk, but for example using led_control in QGC doesn’t do anything. When I send messages using pymavlink or mavproxy from the Pi, I see no evidence at all that these messages are received.

I tried:

  • Resetting the firmware to stock 1.11.
  • Resetting all parameters except the three I need for the connection: SER_TEL2_BAUD = 57600, MAV_1_CONFIG = TELEM2 and MAV_1_MODE = Onboard.
  • I have removed (as far as I know) all references to mavlink, pymavlink and mavproxy from my Pi. I have reinstalled them all, and verified the installation. When I try to connect, I get a heartbeat from the Pixhawk, but basically nothing else.

Does anyone know in what direction I could search? I am a physicist masking as a drone programmer, so a bit of “ELI5” for the more deeply technical stuff is appreciated.

Any additional tests I could run that could bring me closer to an answer are also appreciated, as I am completely stuck.