This subclass of Joint is used to link two Link objects together using a static, or fixed, joint.
Fixed joints do not currently support a relative rotation the way other joint types do. I'm so sorry.
Creates a fixed joint between parentLink and childLink. The joint will be located at parentPoint on the parent's body, and at childPoint on the child's body.
Unfortunately, FixedJoints do not use the relative joint orientation that can be set in Joint. This means that the rotation of the child is always the same as the rotation of the parent.
If parentLink is the value 0, then the joint will be attached to a fixed point in the world, specified with parentPoint.