so ive had this issue for like three weeks now and its driving me absolutely crazy. running a custom build with a brushless gimbal i picked up secondhand, its a 3-axis setup for a Sony a6400 and the roll axis just slowly drifts over time. like it'll be perfectly level when i arm it and then after maybe 4-5 minutes of flight its off by like 4-6 degrees and the footage is basically unusable.

ive done the IMU calibration probably eight times at this point, tried different PID values, even swapped the controller board thinking that was the issue. nothing seems to stick. the weird thing is if i land and re-arm it snaps back to level immediately, so its clearly not a mechanical balance issue with the camera. or at least i dont think it is.

anyone dealt with this before? im starting to wonder if theres something thermal going on, like the gyros heating up mid flight and losing accuracy. not sure if thats even a real thing or im just grasping at straws at this point.

thermal drift on the gyros is absolutely a real thing, especially on cheaper gimbal controllers. the alexmos/basecam boards have a gyro calibration temperature setting you can mess with but honestly on a secondhand unit you have no idea what state the calibration data is in. id do a full factory reset on the controller board and redo everything from scratch, and specifically do your IMU calibration when the gimbal has been running for like 5 minutes so its already at operating temp. calibrating cold and then flying warm is probably your whole problem right there.

also check your motor power settings, if the roll motor is slightly underpowered it'll hold fine stationary but under actual aerodynamic load during flight it starts losing the fight slowly. not a dramatic thing, just a slow creep exactly like you're describing.

had something similar with mine, turned out one of the ribbon cables going to the IMU had a slight intermittent connection and vibration during flight was making it worse. wouldnt have thought to check that but a guy on rcgroups pointed it out. might be worth just reseating all the connectors if you havent already.