Rigging a folding ladder that respect the floor

Question

Im triying to rig a folding stair object and I want the opening movement of it to not cross the floor, or at least the control bone, wich is the one below that controls the movement of the entire rig.

The problem is that when you open it, the angle of the bones is not wide enough to align with the floor:

In the current rig I control the rotation of the bones with a "Transformation" constraint, that translate the vertical movement of a control bone into the rotation of the destination:

Here is the .blend file in case it's useful: https://drive.google.com/file/d/1XwdYS7Js2faWt90WHAYXPKUDdMBkdchQ/view?usp=sharing

Thanks for your time!

Answer 1

A transformation constraint won't do this, because a transformation constraint acts only linearly, and the rotation you want is proportional to the asin/acos of the location. But you can do this with a little creative IK work:

The legs of the ladder are the first bones in a 2-bone IK chain, which has position, rotation, and stretch enabled. The second bone in each chain, which is non-deforming, has IK stretch enabled. All IK bones are locked in all but a single axis. The IK targets are in the same rest pose axes as the second bones in the IK chains.

In order to meet both position and rotation requirements, the second bones need to stay in the same plane as the IK targets, so the first bones rotate only to that plane-- essentially, finding the intersection of a sphere and a plane. Or here, because of the locks, the intersection of a circle and a line.