Hi gyz
M using multiwii 2.5 board I have assembled my quad fully and in acro mode I observed constant drift on random sites so I switched to angle mode then also it drift in one direct
Thing I have tried
1 - checked tx sinagls trim it on exact 1500
2 - calibrated esc again
3 - calibrated acc meter on flat surface
Still m facing same problem plz help me

Which transmitter are you using.
I faced similar problem with F's-ct6b. I was unable to resolve it but it can be solved by adding gps

M using flysky fs-i6 I try to trim it by trimers on tx same issue
And I try to make trim by default setting in multiwii board
(That is (disarmed -trottle up+adjustment roll-pitch-yew)
Still facing same problem

Many people face this problem, Usual fix is to reset the board to default and redo everything. Make sure you remove the props. Also, if not done already, adjust endpoints on the tx and also make sure the gyro is working properly. Adjusting the PIDs afterwards usually solves the problem Good luck