hinging robotic arm

Ok, I need some help. I am trying to simulate the movement of a robotic servo arm I am developing. I need to simulate the hinging or rotational motion of one servo component to the next. I managed to get the first two components out of six to work but as soon as I try to do the third they system falls apart. I realize this is due to the fact that I am using the bounding box.... I am wondering if anyone can help me with this.