when i remove the pin behavior, the head gets very far from the body, so i putted the pin behavior on the head so it doesn't get far.... and i putted the 3 joints because...
1.limited revolute joint : i want to make the head in an locked angle
2.distance joint : because i want to make the head in a locked position to the body.... and it seems it didnt work so i placed the pin behavior.
P.S when i placed the pin behavior, i solved one bug, but i created another bug ..