The minimum motor speed in flight is set too high

What ArduPilot says:

• …SPIN_MIN too high N.N > 0.3

MOT_SPIN_MIN is the lowest output ArduPilot gives the motors in flight, as a fraction of the range between MOT_PWM_MIN and MOT_PWM_MAX: 0.15, the default, is 15% of it. Above 0.3 arming is refused, because so much of the range would be lost to idling that too little is left for control. The message shows the value it found.

What to do, most likely first

1. The value was typed as a percentage (15) instead of a fraction (0.15).

   FixEnter MOT_SPIN_MIN as a fraction of 1.

2. The motors really do need that much to turn steadily: the bottom of the output range is dead.

   CheckProps off: in the motor test, find the lowest percentage at which every motor starts and runs smoothly. If that is near 30%, the range is wrong, not the motors.

   FixWith PWM ESCs, calibrate them so they learn the range, or raise MOT_PWM_MIN to just under the point where they start. With DShot ESCs look at the ESC's own start-up settings. Then measure MOT_SPIN_ARM and MOT_SPIN_MIN again.

3. The value came with a parameter file from another aircraft.

   FixMeasure it on this aircraft, as the Setup & Tuning Guide's idle step describes: MOT_SPIN_MIN a little above the point where all motors run reliably.

Parameters to look at

Where to do it:Setup & Tuning GuideSetup & Tuning GuideMotor & Prop Bench