Keep 4 lines tangent to 2 circles with Stretch Action

[Colin-Pearson]

Hello folks!  I've got a chain hoist I'm working on turning into a dynamic block.  In the attached drawing, the 4 red phantom lines (in the view on the left) represent runs of chain.  They are are drawn roughly tangent to several green hidden line circles which represent the sheaves/pulleys that these chains go around.  I need to make a Stretch Action which would allow the lower assembly (white hook and yellow block) to be dragged further/closer to the upper assembly (white hook, yellow block and green body).  I also need to be able to use a Rotate Action to rotate the entire block.  Through all of this, I need the red lines to remain tangent to both of their respective circles; the one exception is the single that is only tangent to a single circle (and attached at a blue Point on the other end).  ALSO - I'd like these red lines will serve as paths for arrays of the chain links.  I'd really like to avoid messing with custom Linetypes so as to avoid issues with the Linetype getting washed away in an update and/or the Linetype not displaying correctly on other user's CAD setup.  Hoping to get a little input here on the feasibility of what I'm after.  If this is just too difficult, I could approximate the effect by attaching the lines at Quadrant points of all the circles.  Part of the point of this exercise is for me to get better though, so I don't want to take the easier way without giving this a good try.  Working on a solution myself currently and thought I'd reach out to the universe for advice.  Thank y'all so much for reading, and double thanks if you might be able to offer any idea(s)!  CHEERS!

[fkp7057]

You can use Geometric constraint using tangent & fix  after that applied stretch action hope it will help you.

[Colin-Pearson]

I can draw the linework that way, using 2 Tangent Constraints on each line.  Line are shown correctly but when you apply the Stretch Action, and I try to drag the lower portion away from the top portion of the block to lengthen it, the whole block goes along for the ride.  I need the lower section to be grip-stretchable and I need those tangent lines to stretch - that will require that their points of tangency rotate as the stretch happens - that's the part I can't seem to get right.

[Libbya]

You could potentially use a dimensional constraint between the two circles instead of the stretch action.  

[Colin-Pearson]

Hmmm.... that's an interesting thought.  Thanks for the idea.  I'm having some difficulty getting all the behavior I want, but I'll keep working on it.

[Libbya]

Here is a method that is close but not exact.

[Colin-Pearson]

That's pretty neat actually.   I'm going to finish my Constraint version this morning and then maybe recreate the block with this method and see which one behaves better.  As always, I appreciate your help.  Have a great Friday!

[j.palmeL29YX]

In this video you can see an example, how to move the lower part up and down and stay the red lines tangent to the circles. Is this what you're looking for? (Block "test" in the attached dwg).

[j.palmeL29YX]

Attached an improved version (block "test_2) - added a rotation action.

[j.palmeL29YX]

And here still an attempt with two blocks "test_2a" and >>"test_2b"<<. (The video shows test_2b "in action").

[Colin-Pearson]

@j.palmeL29YX  - yes!  Thank you very kindly for your reply.  I have been off of work for the holidays and purposely avoiding email; please don't take my later response as being rude.  Downloading the attached drawing and the subsequent improved one and looking through them now.  Thank you!!!