Current reporting to the GCS, technical question

#1

I am not setup to experimentally verify this question so I need to ask the community.

I am building a VTOL. I am using the cube (Pixhawk 2). I have the PL-Sensor from Mauch. The path of power is this:

Battery red wire to Mauch hall effect sensor to Power Distribution Board.
Battery black wire directly to the Power Distribution Board.

That setup is very standard and will report to me at the GCS (with great accuracy) the amount of current being drawn out of the battery and used by the PDB. This is great, it’s what I want.

If I do NOT use the PDB to power the servo rails on the back of the Cube then I must supply power to the servo rails via a BEC. I have chosen the Castle Creations Pro BEC to complete this powering need.

Here’s the question:
I know that if I connect the Castle Creations Pro BEC DOWNSTREAM (as in connect the BEC’s power IN cables to the PDB Power IN soldering pads downstream of the Mauch Sensor) then I will definitely be reported all of the current being drawn by my power hungry servos because the power going TO those servos must pass through the Mauch current/voltage hall effect sensor.

BUT, as a matter of safety, I have typically used an XT60 that has one side connected to the battery and TWO XT60 outputs. One of these outputs is used to connect the battery to the Power Distribution Board (and thus passing through the Mauch Sensor) and the SECOND output of that XT60 parallel connector I have always plugged in a BEC and then routed that BEC directly to the servo rail behind the Pixhawk 2.1 (and thus bypassing the Mauch current/voltage sensor).

If I bypass the Mauch sensor in the fashion described above will I or will I NOT get the power being consumed by the servos reported to me at the GCS, or will the power being reported to me at the GCS simply be the power being consumed by the aircraft minus the power hungry servos?

I was unable to find anything in the Cube documentation to tell me if there is a magical sensing of power being consumed by the servo rails sense the Cube no longer likes to share power with the FMU (but will share power up to 10.5V with the I/O).

#2

I think you have answered your own question here:
-The current sensor measured the current passing through it
-Current from the battery to the bec does not pass through the current sensor
-Therefor the sensor current does not include the current to the bec, and therefor the current used to power the servos

If you want to include the power to the servos in the measurement, all current from the battery needs to go through the current sensor

1 Like
#3

I was hoping that the pixhawk 2 would have a way of adding to that sensor’s count of amperage all of the servo rail amperage draw as well.

That appears to not be the case.

So I am forced between these two options:

  1. Bypass the current sensor with the BEC so that if the current sensor fails I can at least still operate the control surfaces.

Or

  1. Put the servo rail BEC downstream of the current sensor so that I can get an accurate current draw reading knowing that by doing this the current sensor becomes a single point failure component that will literally de-power the entire aircraft.

PS: I do not want to add anymore batteries than just the main flight battery.

#4

Or add components and code… it’s open source…