Hi @anasarrak @ibaiape, so I reinstalled the apm-copter with the 3.5 stable version, and now at least the pxfmini goes into the 3 light, orange blue green, cycle. But after turning off the power and turning on again, and putting the throttle down to 0, it still doesn't calibrate the esc's.
I can still confirm that the ppm signal is getting to the pxfmini, and can still arm the copter. However, on arming, non of the motors spin until a bit of throttle is put on, and then the 0 point seems to be at about 40% throttle, so above 40% spins the motors one way, and below 40% reverses then to spin the other way. Weird! It didn't do this before.
Also, on disarming the drone, all the motors just stay spinning at a high rpm until battery is disconnected.
I have parameterized as per the post above, and have run through the rc calibration, level calibration and compass calibration a few times now, and no difference.
Any ideas? I reaaaaally want to fly this thing!