I've been trying to make a rotating pendulum (see file for example) but I can't seem to get it the way I want. I started out with a cube and a sphere: the point is to connect the cube which is up higher to the sphere hand have it rotate while lowering just a little bit.
The way I did it was constraining the spline to the cube and sphere and then aligning the sphere to a helix & animating the position. The problem is I want it to look more realistic: rotate the sphere in the right direction + the spline has a deviation I can't get rid of.
the spline deviation (the straighter bit at the beginning I'm guessing you mean) can't be removed with it still a parametric object, you have to make it editable and adjust the first points bezier a bit.
The Tracer is easier for making a straight connection between two objects and doing it between nulls makes the offset to the bottom of the cube easier (one null as a child of the cube and one a child of the sphere - though it does really need the null as the child of the sphere, the sphere could be used by itself).
Rotation of the sphere, depends on the connection, if the line is solidly attached at both ends (no swivel joint) it shouldn't rotate at all.
Helix should be more of a bowl for realism as the length of the connector should be constant.