DJI ESCs and Pixhawk 2.1 on F550 - annoying noise

I am building a F550 Flamewheel hexacopter and after a few problems am almost ready for first flight. I have a relatively minor issue in that the DJI 420 Lite escs beep loudly as soon as the battery is connected and don’t stop until the safety button is pressed - this gives several seconds of annoying cacophony. I think that it is something to do with the PWM signal that the escs are (or are not) receiving until the safety button gets pressed.

I tried disabling the safety button by setting BRD_SAFETYENABLE to 0 but this didn’t change the behaviour (and is undesirable from a safety point of view). I also changed the BRD_SAFETY_MASK to allow the throttle channel to move before the safety switch is pressed but this didn’t resolve the issue either.

I’d be interested if anyone can shed light on this issue and especially if anyone has a solution.


All ESCs will beep until they “see” a valid PWM input.
The only thing you accomplish by disabling the Safety Switch is you disable a safety feature.

So is there any safe way of sending the escs a valid pwm signal before pressing the safety button?

use this parameter

Thanks for the input. Unfortunately it makes no difference. It seems that the issue is not associated with whether or not the copter is armed but whether or not the safety button has been pressed. Pressing the safety button has no affect on anything until the Pixhawk has completed its startup routine then it registers the button press, plays its musical notes and everything goes quiet while it waits to be armed. What I’d like to be able to do is silence the escs earlier. All ideas welcome.


You can use the BRD_SAFETYMASK parameter to allow PWM signals to be sent to the ESCs even when the safety switch is on. You may also need to change MOT_SAFE_DISARM as well.

The safety switch will still prevent arming, but your ESCs will shut up.

Thanks Rick. Tried this with no change to the beeping of the escs - they still beep until the safety button is pressed. I even made all bits of the mask 1 in case I was misunderstanding the channel order.


Not gonna happen.

Pixhawk has a ton of things to do before it is ready to play and all the ESCs have to do is boot and then wait for a valid PWM signal.

Are you certain? I’m pretty sure that should work. Try this:


You must reboot the FC for the safety mask param to take effect.

Rick thanks - I tried what you suggested and it worked - at least the beeping now stops as soon as the fc reaches ‘barometer calibration complete’ in its startup routine. It still seems a long time (8 seconds) with the escs emitting a racket but I guess it’s the best that can be done.