I’m making the switch from APM 2.x to Pixhawk and I have a question about wiring.
As I understand it the power supply to the pixhawk board does not power the output rail?
So I have a 3DR module to power the Pixhawk. Then I have a BEC 5.7v powering the output rail. The ESC servo cable has the (+) cable disconnected. The ESC is powered from the back of the 3DR power module. The 3DR power module and the BEC are power from separate batteries, All components are connected via the (-).
@Lat_Long,
The description of your way you are powering the Pixhawk will work, however I am wondering why you are using a separate BEC for powering the Pixhawk servo output power bus instead of the BEC built into the ESC. Does the BEC in the ESC not provide enough current for you servo power requirements?
Regards,
TCIII AVD
The most accurate answer is “ignorance”. I was not aware my ESC came with a built in BEC, I just checked and its actually one of the selling points posted on the box it came in.
But even so I don’t get a huge amount of confidence with my ESC. If I push the the boat hard with a 3s batt, the batt that is recommended for the boat the 60A ESC overloads and cuts out and then reboots after a few seconds. I didn’t want this to damage the Pixhawk.
And a small part of it is what I have read in other threads; there is talk about power spikes and requirements of a “Zener”. As I don’t have any Zeners I thought that I would just provide a clean 5.7 to the rail.
Also I am building a larger project with will be combustion powered and the 740mm “Relentless” is just a crash (!) test dummy. With the combustion set up I won’t have an ESC so I was thinking why not prove out that set-up on the crash test dummy.
On the larger project I was also considering not powering the rail at all. As I won’t be using a RC, driving via mission planner and a joystick I was thinking of powering the servos directly. So the Pixhawk, the RFD, and other navigational aids are powered from one batt. The servos are powered from a separate batt. The servos are connected to the Pixhawk servo rail via the Signal, and negative wires.
@Lat_Long,
The reason for the Zener diode does not have to do with the power being supplied from the BEC.
It has to do with overvoltage spikes on the servo voltage supply line caused by the operation of the servo itself that can be transmitted back to the Pixhawk servo output power bus.
Regards,
TCIII AVD
TCIII, If the servos are powered by a separate power source, not via the output rail, will that not achieve that same thing as the Zener? Just a little more complicated.