As title says, I am looking for the older version of the pix hawk firmware for the qav 250. If anyone could provide links I would be very grateful.
Try and start here.
Thank you. Do you by chance know the difference between px4_fmu-v5_default.px4 and the px4_fmu-v3_default.px4 trying to install on a qav 250
It depends on your Pixhawk version, e.g. v3 is for a Pixhawk 1 or 2.4.8 that has the updated bootloader to recognize the 2Mb memory. A quick way to find out what your FC uses is update it with the current stable firmware and watch which version it uploads.