Adjust PWM sent to ESC in disarmed state to avoid ESC beeps?

ArduCopter Copter 3.2
1

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” [1]. 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):

[quote]PWM Values
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…

[1] DJI E300 manual, pdf available from here

2

(I can’t find the edit button…)
I found the following thread describing a similar problem, although in that thread the motors didn’t start (the motors do start in my case). I tried setting the RC1_MIN value to 1022 as suggested anyway, but that didn’t remove the beeping.

BTW, here’s my version info:

[MAV 001:1] ArduCopter V3.2.1 (36b405fb) [MAV 001:1] PX4: ce602658 NuttX: 475b8c15

3

I had the same problem and never really resolved it. I ended up flashing my ESCs to BLHeli custom firmware (for unrelated reasons) and it doesn’t have the same annoying no throttle beep.

4

I see.
Do you have the same DJI E300 Opto ESCs? If so, do you have a link handy about the procedure?
So I read the PWM values that come out of the Pixhawk using an Arduino (pulseIn seems to be the function that you need), and it looks like the APM:Copter firmware doesn’t send anything while the Pixhawk is disarmed:

hi - printing PWM on pin 7
0
0
0
0
1117  <<armed
1109
1111
1102
1109
1109
1109
1109
1096
1109
1109
1109
...
1109   << disarmed
0
0

I did dig in the code once already… at the time I got the impression that the motors would send the minimum throttle stick value, but clearly that’s not the case.

I think this leaves me with 3 options:
[ul][li] fix/improve the code so that it sends a min throttle value when disarmed[/li]
[li] Look into flashing ESCs with BLHeli[/li]
[li] Look into using the PX4 flight stack[/li][/ul]

Unfortunately it looks like I need to RMA my Pixhawk for unrelated reasons, so it might take some time before I find a solution to this problem…