After the airframe is setup and configured you should validate the motor assignment and spin direction, and the servo response. This can be done in QGroundControl, under the Vehicle Setup > Motors tab.
Note the following PX4-specific behaviour:
- If a safety button is used, it must be pressed before motor testing is allowed.
- The kill-switch can still be used to stop motors immediately.
- The parameter COM_MOT_TEST_EN can be used to completely disable motor testing.
- On boards with an IO, only the MAIN pins can be tested.
- On the shell, motor_test can be used as well, which has additional options.
If one or more of the motors do not turn in the correct direction according to the configured airframe, they must be reversed. There are several options:
- If using ESCs that support DShot you can reverse the direction via DShot commands.
- Swap 2 of the 3 motor cables (it does not matter which ones).
If motors are not connected via bullet-connectors, re-soldering is required (this is a reason, among others, to prefer DShot ESCs).
The following additional checks should be performed to validate that the vehicle is setup correctly:
- With propellers still removed, switch to Stabilised mode (Multicopter) or Manual mode (Fixed Wing) and arm the vehicle.
- Increase the throttle a little (so the vehicle does not automatically disarm) and check that the motors respond to throttle changes.
- Check that all motors spin at minimum throttle.
- If the vehicle has ailerons, check if they are responding in the right directions when giving roll/pitch stick input commands.