This has been a pain for the last couple days for me, in the example I hand keyed that one but looking for a better solution that escapes me for the moment. Everything Ive tried has failed. Basically this is a wire loom that acts sort of like a tank track except one end stay stationary and the other moves with with equipment its attached to. Unfortunately this is all I can show at the moment but hope its clear enough. Any advice or input will have my undying thanks and a couple rounds of beer if we meet in person 
Path deform modifier (World space) would be my first thought. Simply animating the spline pulls the track with it.
I did try them as a path deform but the problem was the “C” curve and keeping the spline the same length at all times so it doesn’t disconnect the loom at either end, which also lead to key framing by hand on every frame and for this job thats just far too keys Id have to enter.
*EDIT*
I also tried animating a bend modifier center point gizmo which still resulted in keying every frame but also makes the viewport very slow.
If you add a “normalize spline” modifier to the spline it should clear up any stretching. The curve points on the spline then get animated half as much as the anchor object. It doesn’t really matter then where the spline ends, only where it begins. I made a quick scene if it helps.
Track.zip (439 KB)
Cool beans thanks much Ill check it out
Just rereading my post…just to clarify-the curve points of the original spline get animated, not the curve points on the normalized spline version.
Not sure if it helps but you might be able to achieve something like this with RailClone. For the C curve RailClone can bevel the spline automatically.
A sample file is attached, it should work with the free lite version of RailClone.
Cheers,
Paul
trackwithRailClone.zip (104 KB)
Im not sure if I understand, there is only one spline that I can see in the scene.
Thanks Paul, I don’t have RailClone but might give it a try if I cant get it to work otherwise.
Ive been able to come close with the attached solution, Im trying to wrap my head around the PathDeform mod but still working on that lol. Ive trashed my shoulder bad and the pain meds are slowing me down a bit today lol. Ive attached a screen and the scene with notes in it to hopefully explain it a bit better.
DK_Track02.zip (289 KB)
This might work. Create a dummy object, attach it to base assembly and wire it’s position to the top assembly but divided by 2.
Then select the verts on the C curve and apply a Linked X Form operator. Pick the dummy as the control object. As you move the top section the C curves moves at half the speed maintaining the correct spline distance (hopefully)
Should work with Path Deform as well as RC 
DK_Track02_1.zip (223 KB)
Some of that is greek to me but Ill do some reading on it downloading railclone now to give it a shot. Thanks again Paul
Actually, keeping it simple - here’s a version that uses your bend modifier technique. The Bend modifier’s gizmo is wired to the Y Position/2 of the top assembly (+ an adjustment value to move it back to the correct position).
DK_Track02_2.zip (280 KB)
Thanks again Paul, your help is greatly appreciated I did try the first one and to my surprise successfully made one with the path deform but I noticed the meshes deform a lot as the path changes. I might keep going with the first example you sent with RailClone and hopefully the lite version will work for me for now. The company I work for has a buying freeze on at the moment with no end in the near future in sight so my options are limited and thanks to the over paranoid IT dept here when ever there is an update or new software I need installed I have to have them install it and sometimes its a real pain in the but as I’m the only one in the company doing this stuff and they dont understand the software at all and cant figure out why it cant just run like ms office lol.
No problem at all, glad it was helpful and it’s always interesting for me to see if I can find new and unusual uses for RC. Best of luck with the project - it sound like an interesting challenge!
Cheers,
Paul