Servos driving to endpoint

Hi everyone,

I have run into a strange behavior of the servos using PX4 (1.11 stable) on Holybro Durandal.

When the power to the flight controller is cut, the servos (being powered from separate source) are driving to their endpoint (in the high-pwm direction) and stays there until the flight controller regains power. However when I disconnect the servos from the signal ports they have normal behavior, implying the cause of this is in the flight controller.

I have tried to find failsafe parameter that could affect it but with no success.

Does anyone experienced similar problems, or have idea what can cause it?

If you cut power to the flight controller then there is no fail safe. If the flight controller is off what is supposed control the fail safe? There is nothing driving the servos at all. It’s normal and expected.

If the flight controller cuts off in flight it’s pretty much over you are going to crash.

Thanks for your help. We would have expected it to go to the low pwm direction, though (or do nothing at all).

Also, we have an airship so it wouldn’t crash upon the lost of the flight controller, but would continue to float. We added a reboot mechanism indicated from the transmitter, to regain control in case of any firmware problem during flight, so we are cutting the power on purpose.

If this is the failsafe happening you can always set the failsafe pwm using




Unless there is no power to the FC.
If the FC has no power none of the setting mean anything, because there is nothing driving the PWM lines.