Troubleshooting VTOL Quad Tailsitter Surfaceless Drone

Certainly! Here is the corrected version of your text:

Hello everyone,

I am currently working on a VTOL Quad Tailsitter drone with no control surfaces like elevons, rudders, etc. More specifically, it’s going to take off like a multirotor drone and then transition to a fixed-wing UAV. The differential thrust of the four motors will be utilized for controlling the fixed-wing configuration. I’m using the PX4 as the hardware and PX4 1.13 as the firmware.

During the tests I have conducted, when the drone tries to transition from VTOL mode to fixed-wing mode, the drone’s nose pitches down. The pair of lower rotors tries to pitch the nose up unsuccessfully. In the image below, you may see this phase of the flight. However, as can be seen from the image, the set of upper motors has a significant gap in their operation, as if they are not working at all.

Does anyone have any idea why this is happening or can explain why the motors behave like this in the red circles in the image?

Thank you in advance for your answer.