ESC powering Pixhawk?

My project uses a trolling motor with a 30amp ESC. Prior to using the Pixhawk, my ESC would power the RC receiver. Now when connecting the ESC to one of the Pixhawk main output signal pins, it powers up the Pixhawk.

I’m concerned as this bypasses/negates the power module and I don’t know if the power from the ESC is regulated.

The wire running from the ESC is the standard pos/neg/signal (yellow/red/brown). Should I just blank out the positive and negative coming from the ESC to prevent it from powering up the Pixhawk?

Also, can I use the ADC 6.6v from the Pixhawk to power my RC receiver? Has this been done?

Here is the ArduBoat Wiki section on how to attach and power a receiver when using the Pixhawk.
The Pixhawk will use the ESC BEC power as a secondary power supply if the primary power supply should fail.
However, I have had issues with the Pixhawk randomly rebooting when using ESC BEC power input to the servo output power bus when the voltage exceeded 5.5 vdc.

Probably need to add the Zener when using power on the Servo Rail

I Don’t use a Zener on my boat or helicopter and run the rail at 5.7 volts. Maybe I’ve been just lucky?

David R. Boulanger

Hi David,
During the early days of Pixahawk Rover testing I had a number of wild Pixhawk out of control resets until Tridge setup the Pixhawk to put out a neutral signal upon a reset or at startup.
We later found that the resets were being caused by the 6 vdc coming from the Traxxas ESC BEC though the word at the time was that the Pixhawk servo output bus should be able to handle up to 20 vdc.
So I just bypassed the ESC BEC around the Pixhawk servo output bus and went directly to the steering servo.
Though I do have the zener in place on my Pixhawk controlled model planes to prevent spikes from servo operation from resetting the Pixhawk.

The preferred option would be a diode and making sure the BEC output from the ESC is at a suitable voltage to enable it to power the Pixhawk if required for redundancy. A quicker and easier option would be to remove ONLY the positive pin from the ESC servo lead so you no longer provide this voltage to the Pixhawk. You MUST leave the ground wire connected (as well as the signal obviously) to avoid all sorts of floating signal level problems with the ESC. Also note that this will also remove this level of redundancy from the power supply to your Pixhawk.

Hi David
I’m a newbie here. What do you mean when you say “run the rail at 6.7 volts”.

Thanks billb (and others) for your help

I’m new to all of this. I’ve seen the term ‘servo rail’ in other comments/help docs, what does it refer to?

Thanks for your help

Each 5v pin on the servo connector edge is connected to each other. I.e in a line. It’s referred to as a ‘rail’

All the GND pins are connected as well