so ive been dealing with this for like three weeks now and i cant figure out if its a hardware issue or something in the settings. running a Gremsy T3V3 with a Sony a6500, works perfectly on the bench, motors are balanced, everything looks good. but about 4-5 minutes into a flight the roll axis starts slowly drifting to the left maybe 2-3 degrees. not a huge amount but when youre doing a slow pan shot its completely obvious in the footage.

ive recalibrated the IMU twice, checked all the motor tuning, tried different gain settings and nothing is really sticking. the weird thing is it seems worse on warmer days which makes me wonder if its thermal related somehow? or maybe the motors are heating up and losing torque? i dont know. anyone dealt with anything like this before with a Gremsy or really any 3-axis gimbal acting up mid flight

thermal drift on the IMU is absolutely a thing, especially on the Gremsy units. the gyro inside is pretty sensitive to temperature changes and if the housing heats up unevenly you can get exactly what youre describing ? slow roll drift that gets worse as the flight goes on. try wrapping some foam around the IMU housing to insulate it a bit, sounds dumb but it actually helps. also check if you have the notch filters tuned correctly because motor heat causing vibrations that change in frequency as temps rise can fool the PID into chasing itself.

might be worth checking your motor balancing again but like really carefully ? i had something similar and it turned out one of my camera mounting screws had worked itself slightly loose over a bunch of flights and the whole payload CG was just barely off. the gimbal was compensating fine when cold but as things loosened up thermally it couldnt keep up. probably not your issue but its worth 5 minutes to double check before going deep on the firmware stuff