Tailsitter (mode = 2) "surfaceless" roll authority (and q_assit behavior)

ArduPlane
1

Hello everyone, I’m posting this to ask for help with a specific issue, particularly regarding PID tuning.
My platform is a quadcopter-style drone with a fuselage (4 kgs weigh, 6s battery with 3115 1250kv motors), operated in ArduPlane mode with transition capabilities. Control surfaces are emulated using the motors (tailsitter mode = 2).

1)I’ve noticed various issues at high roll angles where the PIDR controller fails to track the target setpoint (matching “roll desired” to actual roll).I realize this could be due to insufficient thrust, but the PIDR.Act value also seems odd at times.

2)Furthermore, when the roll angle becomes excessive, “q_assist” kicks in, and it seems to make matters worse rather than better (causing severe oscillations). Do you think it should be disabled for this type of tailsitter?

Thanks in advance to everyone for your help !

Here is the log : https://drive.google.com/file/d/1U-qvPpAbyLIwDKfbsJY0n8yoM-axjSpw/view?usp=sharing

Capture d'écran 2026-07-05 175951
Capture d'écran 2026-07-05 1759511510×717 139 KB

Problem apperas as well with light angles : PIDR.act seems to add an offset when on left roll :

Capture d'écran 2026-07-05 183821
Capture d'écran 2026-07-05 1838211470×608 132 KB

2

Do not put your questions in code blocks it makes it hard to read.

Only code and ASCII art belong in code blocks.

3

sorry , just corrected

4

Don’t forget about the 90 deg reference frame shift. For roll control in forward flight you should be looking at PIQY. PIQR would be fixed wing yaw.

5

Thanks for your answer.

But when i analyse logs, PIQY.Act does not seem to reflet AETR.Ail, and PIQR.Act does.

Do you have an idea ?