Mech arm animation problem


Hi everyone,

I dig through old threads but couldnt find what I look for. So I build mechas with Maya but recently I’m having a problem with animating mech’s arm. I rigged the model but when I rotate torso, arms doesnt follow it and keep pointing the same direction.
I added 2 screenshots for before and after the rotation.

I highly appreciate if you can give me tips and tricks.