so ive been fighting this for like two weeks now and im at my wits end. running a 3-axis brushless gimbal on a 5inch quad, the camera is a runcam hybrid 2 and the gimbal controller is an stormbeest sbgc knockoff basically. the issue is that after maybe 3-4 minutes of flight the horizon starts to creep, like maybe 2-3 degrees over time. it doesnt snap back it just slowly drifts and then eventually the gimbal hits a soft limit and stays there.

ive recalibrated the IMU like four times, tried different follow modes, even reflashed the firmware. nothing seems to stick. the motors feel warm after a flight but not HOT hot, and all the balance points look fine to me when i hold the rig level. could this be a PID tuning issue on the gimbal controller or is there something else im missing

classic sign of IMU drift, usually happens when the gyro temp changes during flight and the offsets arent being compensated properly. on simplebgc boards there's an auto-tune for the gyro temperature compensation but you have to actually do a full warm-up calibration sequence, not just the quick static cal. basically you let the board sit powered for like 20 minutes, then do the cal while its at operating temp. most people skip this and do it cold and wonder why it drifts.

also check your motor balance. if one axis motor is working harder than it should, could be your roll motor is slightly underpowered for your payload, and over time the PID integrator winds up and you get creep. whats the total camera+gimbal weight looking like

had almost the exact same thing on my 7inch build, turned out one of my gimbal motor phase wires had a tiny cold solder joint and it was basically missing steps intermittently. the drift was really gradual so i thought it was software but nope, just a bad connection. worth checking with a multimeter if you havent already