Throttle response fails in disarmed manual mode

Throttle on fixed wing responds to Tarranis throttle lever in “Armed Manual” mode but not in “Disarmed Manual” mode.
My concern is not being able to disarm Pixhawk 4 while running Q Ground Control and be able to manually fly the aircraft back with throttle available., All other controls function normally.
Any pointers on where to go to resolve the issue greatly appreciated.

I’m confused. So what exactly are you seeing and what would you like to see?

So one thing is that disarmed, the throttle should (of course) not work because that would be a safety concern.

Hi JulianOes,

Thank you for the prompt reply. I’m an avionics tech on full scale aircraft starting with the F-14 Tomcat working through various civil jets ending up here on Pixhawk4 which I’m still learning.

I was under the impression that disarming Pixhawk4 would remove the flight controller from the aircraft control loop and return full control back to the RC transmitter. As if the Pixhawk was not installed. Under those circumstances the throttle control would need to be available to the RC controller. This essentially returns the aircraft to a standard RC aircraft in the event the Pixhawk should fail in flight; the option to fly the aircraft as a conventional RC aircraft still remains.
From a safety standpoint I don’t see how taking the autopilot completely out of the loop would be unsafe. However I do understand the current convention. I am also flying successfully at this point so I’m content. Again, Julian, thanks for your time.

Ok, so PX4 and the Pixhawk 4 don’t do passthrough of the RC signals if disarmed, however, they do have something similar to the safety feature that you want, I believe.

The way we try to make sure that “manual override” is always possible, especially in the case something of the flight controller should fail, is that the Pixhawk 4 consists of two processors (also called FMU(main) and IO board). The IO part basically, only does mixing and fail-over switching to manual mode if the pilot wants to override using the mode switch, or if the FMU stops sending commands because it has crashed or locked up somehow.
Since the IO code is therefore safety-critical, it is changed seldom and kept fairly simple.

I hope that is helpful (and I’m wondering if that’s documented somewhere because it should be).

Hi Julian,

Thank you again for your reply. Please pardon my response rates as I’m trying to run an international company at the same time. In fact if UAV automation and coding/scripting is your thing then I would be open to flying you out to Thailand for a week or two for assistance depending on your situation at home. We have a lot going on and our systems are rather large and expensive. We will be working with Micro Pilot autopilot systems as well as Pixhawk 4 and some hefty payloads should you care to assist integrating all this. Our Radios are Mimo.

Back on topic, so I understand now the IO code is the core safety element based on fall-over, I dont write code but I understand it. C++ was the thing back in my day.

Next issue I have is getting the aircraft to takeoff in in Q Ground Control. When I upload the flight plan, arm the aircraft then select “Mission” it does nothing. Advancing the throttle in manual then selecting “Mission” while in motion has resulted in two takeoffs but this isn’t correct. Any thoughts or even just a step by step process of planning the takeoff waypoint and sequence to upload and fly would be hugely beneficial.

If the topic re. Thailand is of interest my email is

Nevermind the Q ground Control take off question. I have it working fine.

Sorry for the late response, I got busy as well. I’m afraid I’m rather busy already (I work for Auterion) but thanks for the note.
And to find PX4 contractors, make sure to check the #jobs channel on the PX4 slack if you haven’t already done so.