I want to try to tie a curve, or a mesh (just a simple thin cylinder) between certain verts on two other objects. Similar to a chain on a draw bridge it will always be taught so needs to change length, not fold.

I’m pretty sure this will be achieved with constraints, but I’m completely new to those. Could someone point me in the direction of a tutorial or article for this?

The way to rig a curve to be tethered between two objects is to add Hook modifiers to the vertices of the curve, with the target as some other object, or a vertex group of some other object. So the Hook target can become a vertex group of the target object, which can be just one single vertex. Hook modifiers move the vertices of the curve so if you add hooks to each end and drag them apart the curve will get longer, move them together and the curve gets shorter rather than folds up.

Let me know if you can understand and do this, I can always make a quick mockup for you.

I don’t know of any tutorial to do this, but a quick look at the Manual for Hook mods will show you all you need to know.