I had a problem with my quadcopter being very unstable and occasionally flip on take-off. It is flyable but is very difficult to hover. Someone suggested that I should check the PID settings. However whatever I tried all possible PID values and nothing seems to work so I doubt if that’s the problem.
If I have this problem I would try using a different flight controller, to rule out the variables of hardware issue. If any flight controller gives the same result, I can then move onto troubleshooting the hardware. If one flight controller works, then it’s probably the software or PID settings.
To troubleshoot this instability problem with hardware, I first use the GUI as a diagnostic tool, making sure my Gyros and ACC works correctly and the numbers and 3D model is matching up to the corresponding movements. I also check out the Radio control input being correct as well.
If everything is correct so far, I move onto the motor, listen to the noise and vibrations when they are running, and make sure the shafts are straight.(same with props etc). It could be possible that the motors might have bad bearings and they are properly balanced, same for the propellers as well. Bad motors or damaged bearing will likely to cause the quadcopter to be unstable. You can confirm this if you have a watt meter, that damaged motor will be working harder and pull more amps than the rest. Also will get warmer faster. Small chance that its slightly damaged and wont do this, but since any drag will slow it down, I would replace it. Then move on to the frame, make sure every slot is seated and everything lock tied and tight.This would pretty much cover all aspects of the hardware.
That’s pretty much I would do to check my hardware. Re-calibrate the sensors and try to tune the PID values settings again. It’s also always good to have spare motors, and frame, to replace and try again.