LookAt while Hinge Jointed

[Stalli]

I do not understand, why jointed object can’t look at target.

Example: 2 boxes with hinge joint (anchor is at the touching place) and a target object. When I say A-box to lookAt target, I think it will just turn on X-axis. But both of the boxes start to shake. Why?

[32433-безымянный.png|32433]

[_MGB]

Hinge joints constrain the objects to rotate on a single axis like a door. The boxes are probably shaking as the physics solver tries to bring the pointed object back under this constraint.
You could try a configurable joint instead?