Pixhawk Servo Rail: No output

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1

Hi Folks.

I am posing a question here as I am sure that someone out there has encountered the same issues I am encountering. I really need some help with this one.

The issue is that none of my servos work all of a sudden. My prop works but the servos are dead. I’m using a plane by the way.

I have tested the servos one by one and they are not the issue. It would seem that the servo rail no longer provides power to anything…

I have my ESC plugged into the throttle channel and this is where the power for the rail comes from. The rest of my servos are plugged into where they should be. I’ve had countless great and poor flights.

With everything connected (all the peripherals, battery, ESC etc for nor,al operation) I arm the pixhawk. The motor does its beeping and booping. Any input from me with the transmitter does nothing unless I move the throttle, then the prop spins as it should.

Measuring the voltage on between the signal and ground cables on the servos I get a static reading of 0.21v. When I move the sticks the voltage will increase or decrease spending on the direction of movement by about 0.15-0.2.

Measuring the voltage on the throttle (from the ESC) I get 4.91v between signal and ground…

Are there any hardware specific diagnostics I can do? Can anyone assist me in any way with this??

I am at such a loss…

2

What about the hot lead in the esc plug?
Do you get voltage between it and ground?
Try just applying power and ground from a bec at the thro input on the pixhawk and see if the servos move then, if they do then it would seem you may have a esc issue or even a broken wire in the esc lead.
You can check continuity on the esc leads as well…
Hope this helps…
One last thing, is the plug inserted correctly?? polarity wise…

3

captmark, thank you for your input!

I am out of town at the moment but it would seem that your suspicions are correct, the ESC’s BEC is to blame.

When testing the plug from the ESC I get the following results:

Between + and - the voltage reading is 0v.
Between + and signal the voltage reading is -4.91v
Between signal and - the voltage reading is 4.91v

So the ESC appears to be the problem here.

I am out of town at the moment but as soon as I get back I will test everything with a fresh and confirmed-to-be-operational ESC and report back.

The cause of this issue is still unknown.

4

Good Day, Folks.

I figured I would update anyone who stumbles upon this.

The issue was indeed with the ESC’s BEC. I replaced the ESC and power was restored. Full servo function enabled.

I hit a little hiccup with the 3.3 firmware which required full arming and all the arming checks (I was bench testing indoors and had no GPS signal) so the motor didn’t spin up no matter what I did. Fixed that up though by poking around the parameters puzzling. SHould really have read the release notes… anyway.

Did a flight too. I attempted to try and tune a the airframe a little better. Sadly that didn’t work and I hit a stall in the turn resulting in a ‘salvaged crash landing’ by flipping to manual at light speed so now I am waiting on my latest fiberglass fix to cure… I don’t know why I cannot get the tuning on this frame to work out. It is so frustrating!