4 + 1 VTOL mixer interaction with pusher motor

[Sibre3]

Regarding a conversation @sensei-hacker and I had on INAV discord.

When a 4 + 1 VTOL plane is operating in mixer profile 1 and the throttle input from the stick is lower than 1300us. Any motion on the roll or pitch axis will cause the pusher motor to increase in rpm until motion on that axis becomes stationary again.
This can be heard and seen in the log provided.
It occurs during fixedwing auto-launch and in normal fixedwing flight when VTOL mixer profile 1 is active.

I have tried multiple motor, servo and timer allocations. From having S1 to S4 as the lift motors and S5 as the pusher motor. Which is more conventional.
To having S1 with nothing. S2 as the pusher motor and S3 to S6 as the lift motors. Which is the way it is in the log. All mixing methods work correctly in my tests. But the issue occurs regardless.
If relevant VTOL motor mixing is removed from mixer profile 1 and mixer profile 2 is erased. The pusher motor works as it should in normal flight or auto_launch.

I considered airmode_throttle_threshold which is 1150us and lower than 1300us. It also has airmode_type = stick_center as recommended.

A rundown of the log which is a bench test.
It commences with fixedwing auto-launch and a shake to start operation. I then move the nose of the plane up and down and roll left and right to cause the motor rpm to change with axis movement. When auto-launch is complete I continue to do the same with the throttle below and above 30% to show the results.

There are several serious short falls INAV VTOL handling has. With fixes in their own time. But there is one other I would like to mention which as bad consequences. But should be a simple fix.
Due to failsafe_throttle being located in the battery_profile. It can not be altered between fixedwing and multicopter operation. It would help considerably if that setting was in the control_profile. Because you want it at 1000us for a planes mixer profile. And just below hover throttle for the VTOL mixer profile.
Otherwise if a FS and GPS loss occurs in VTOL mode with failsafe_throttle = 1000 . The aircraft will shut off the lift motors and drop out of the sky. Or if it occurred in the plane profile with failsafe_throttle = 1400us. The plane would fly away.

• FC Board name and vendor: MATEKH743
• INAV version string: 9.0

LOG00002.TXT
VTOL 4 + 1 diff.txt

[Sibre3]

I forgot to mention the other throttle related issue we spoke of in the discord chat.
You may or may not remember me saying there is a problem with the throttle output reaching 100% at a stick value of 1750us.
This occurs in every flight mode. Even in RTH and FS.

This means when RTH is triggered and the plane starts to climb. It should do so at nav_fw_max_thr = 1750. Which is what I have it set.
But instead the throttle max's out at 100%. Making all navigation climb settings void at full throttle. Including nav_fw_allow_manual_thr_increase = ON at lower climb angles. And all nav_fw_pitch2thr related functions. Which means there would be no throttle reduction below 100% even when the plane is trying to descend at the home point.

FYI. When I ran these tests. I did so firstly with all the VTOL mixer profiles loaded.
And the second test was done with the plane only setup as a fixedwing. No VTOL mixing at all. This is how I observed the difference in throttle output changes.

I could only find two people that posted usage of this feature on discord. And no video's on Youtube. Maybe because they never thoroughly tested it. Or lucky for them didn't require RTH or FS.

[Jetrell]

@Sibre3 Your comments reminded me of these bugs. And why I switched my quadplane to AP.. It's funny it didn't even occur to me when I run the test for you the other day, and replied on Discord.
I experienced these problem back in early 2024. The feature was implemented in late 2023.
At the time I tried to contact the collaborator who wrote this feature, in a DM. However he wasn't around at that time. And I completely forgot of the issue until now.

@P-I-Engineer @shannonbaker If my bad memory serves me correctly. You are the only two guys and one other, that posted of making an INAV 4 + 1 build.
Did either of you actually use RTH on those specific builds ? Or run fixedwing Autolaunch ?
Back then when I ran my tests. I didn't end up using the feature because Shota didn't back in contact with me about the problem. So I wasn't going to risk the model.

[P-I-Engineer]

I used fixed wing auto launch. Not sure I ever did full rth.

I did add a note I. The docs about 4 and 1 and motors spinning up.

[Jetrell]

I used fixed wing auto launch. Not sure I ever did full rth.

@P-I-Engineer I found your plane. From what I can see of it. It wasn't a 4 + 1. But rather a Tilt-rotor quad. Just like a tricopter. Except it had two lift motors at the rear.
So it wouldn't likely have experienced the issue in this report.

[shannonbaker]

I have only used VTOL take off and VTOL transition in the manual landing sequence. I have not used autolaunch. I don't recall using RTH but I think I would have but unsure as I flew this model a long time ago.

@P-I-Engineer @shannonbaker If my bad memory serves me correctly. You are the only two guys and one other, that posted of making an INAV 4 + 1 build. Did either of you actually use RTH on those specific builds ? Or run fixedwing Autolaunch ? Back then when I ran my tests. I didn't end up using the feature because Shota didn't back in contact with me about the problem. So I wasn't going to risk the model.