I’m setting up a new quadcopter using a 2.4.8 Pixhawk FC and PX4 firmware. After doing an initial set-up and calibration, the motors will arm when the FC is plugged into the computer via USB. They won’t arm with just the radio transmitter. Any suggestions?
You need to figure out why it’s not arming. Easiest is to get telemetry using an SiK radio like this: SiK Telemetry Radio V3 – Holybro.
Otherwise, you can also enable logging from boot and then check the logfile if there are any hints why it didn’t arm.