Can pixhawk RC1-8 passthrough on 2nd CPU save my plane?

ArduPlane Plane 3.3
1

So I know that the pixhawk has a safety where if the main CPU fails (and by that I assume the code), the 2nd lesser CPU can bridge the first 8 RC channels, which in the case of a plane will let you fly in manual mode even though the autopilot is dead.

I was just curious: when can this save me?
Arduplane code bug, crash/reboot?
Hardware failure? If so, which one(s)?

Arducopter doesn’t have this feature obviously, so I’m just wondering how often this pixhawk feature comes in handy, if ever?

And I’m asking because my new plane is vtail and it’s complicated if both my controller and the arduplane do vtail mixing…

2

Well, if you are really doing risk analysis at this level, yes, a crash can bring the plane down - even with a bypass , it’s not al situations along a mission you can handle with a full crash (since telemetry stops as well)

  • then you can start looking into AP redundancy.
    but to be realistic . the MTBF on a healthy (not correded/or mechanically damaged) Pixhawk, with redundant power supplies, will always beat the MTBF of your servos. then you have to think about the other possible single point of failure, like RX, Radio.

It also runs NuttX which can help if some routine were misbehaving (not just get stuck).
For highest reliability, you should usually start with redundant power, servos, and telemetry.

3

Thanks AndreK, so to be clear: the RC passthrough that’s supposed to happen on channels 1-8 if things go wrong in the pixhawk, isn’t really useful and in real life doesn’t really get triggered.
Is that correct?

4

Depending on how you mean it.
It would be useful if software crashed and you had a UAV that could be directly controlled via passthru (no complex plane mixing, or ArduCopter)

“isn’t really useful and in real life doesn’t really get triggered” in the sense of " I have not seen it kick in ever, nor did I ever seen a Pixhawk fail - and a passthru would not help during a longer mission once it’s beyond flyable VLOS"

5

Thanks AndreK.
Note that if you’re flying FPV, it’s ok if it fails beyond LOS since I usually fly manual anyway, but I agree that for most other folks, it’s not.
Either way, as long as you’re saying that this passthrough feature doesn’t seem to be used often at all, if at all, I’m not too sad about losing it then.