I’ve got a DJI F450 with a Pixhawk flight controller (APM flight stack) and DJI’s E300 Opto ESCs. When the Pixhawk is disarmed, the ESCs beep every second, signalling that the “Throttle stick is not at bottom” . This is very annoying, since the beeping is rather loud.
I’ve checked the troubleshooting wiki article, but the suggestions there don’t help - my RX/TX setup is fine, as I can fly the quadrocopter, I can’t calibrate the ESCs since they are optos, and I don’t think it’s the startup signal issue since the beeping restarts after landing and disarming the quadrocopter.
The closest I’ve come to a solution to this problem was discovering the Pixhawk.org wiki’s PWM ESCs & servos page (emphasis mine):
The PWM value sent out depends on the flight stack and configuration used. Most ESCs require to see a low value before they allow to spin up the motor at higher values (to avoid having an user who has his throttle stick in the middle position on power-up hurt himself). This low value barrier varies between roughly 1200 and 900 us. The native stack therefore sends a value of 900 while being disarmed to ensure the ESC sees a valid low pulse. Other flight stacks (e.g. APM) might behave differently.[/quote]
I suspect that whatever “low” value the APM flight stack sends (if any) isn’t suitable for my ESCs. I’ve tried looking through the full parameter list page, but haven’t found a setting for it. The at first glance “obvious sounding” THR_MIN parameter doesn’t seem quite right (“The minimum throttle that will be sent to the motors to keep them spinning” - I don’t want them to spin, I just don’t want the ESCs to beep in disarmed state).
Any ideas how I can prevent the constant beeping?
I don’t think I’m alone in facing this problem (see e.g. West’s comment here), but I haven’t managed to find a solution…
 DJI E300 manual, pdf available from here