so ive been dealing with this for like 3 weeks now and its driving me nuts. running a Gremsy T3 with a Sony A7III and every time i get maybe 10-15 minutes into a flight the horizon starts to slowly creep. like maybe 2-3 degrees over the course of a minute, not a sudden jump, just this slow drift to the left side. re-calibrating on the ground fixes it temporarily but it comes back mid flight every time.

i dont think its the IMU because the drone itself is holding position fine, its definitely the gimbal. ive tried re-seating all the ribbon cables, checked motor temps after a flight and they seem normal. payload is right at the edge of the Gremsy's rated limit but ive flown heavier with no issues before on a different rig. anyone dealt with this or have any ideas before i start swapping parts

had almost the exact same thing happen with a Ronin variant a while back. turned out to be the PID tuning drifting under thermal load, the motor was working harder as the arm warmed up and the gains weren't compensating. if your gimbal software lets you log motor current or effort during flight thats worth pulling. also check if the drift direction changes when you swap which side of the aircraft it's mounted on ? if it follows the gimbal orientation rather than staying fixed relative to the horizon thats a strong sign its a tuning issue not mechanical.

the payload being at the limit is probably making it worse too. even small imbalances get amplified when the motors are already working near their ceiling

might be a dumb question but did you balance the gimbal with the actual lens you're flying? i ask because i made that mistake, balanced with the 24-70 then flew with the 85mm and got creep on the roll axis. camera was technically under the weight limit but the CG was off enough to matter