I’m attempting to power the Pixhawk via the servo rail as a backup in case the power module were to fail for some reason.
If I try to boot the Pixhawk with only the servo rail powered, neither of the FMU lights turn on. the PWR and B/E light for the I/O section turn on and the ACT light flashes. The Pixhawk does not boot up properly and the main heartbeat light does not come on.
The UBEC is on a Quattro ESC, it’s providing 5.27V, it is plugged into one of the “Main Out” ports on the Pixhawk
Is the Pixhawk not meant to be powered from the servo rail, or is it obvious from the description above that I’m doing something wrong?
You did read the documentation and do use a Zener diode, right?
I did read the documentation, I have not added a diode. I understood that to be a precaution when there are servos attached, have I misunderstood and that is required for the Pixhawk to be powered of the servo rail?
It’s not required but recommended. I’m just making sure, all relevant information are here.
I am having the same issue and I didn’t add a diode. Apparently I didn’t see that in the documentation.
I just got some update today on that. The diode is mainly to filter out servo spikes if you have servos.
When double powering, the FMU can reboot if there is some noise on the line of the power module and the system tries to switch over to the BEC on the servo rail. However, that should only be a problem if the BEC supplies more then 5.7V, because then the protection circuit will kick in.
I’ll try to get some 3DR engineer to look at that.