I don’t have a problem with the blender shapes or rig when they are not controlled by a bone. It is when I try and get them to connect via a Bone have the problem. Your tutorial looks really helpful. I will have to go through it when I have some more time.
I think 100% of my problem is around the driver I am using to tie it to the bone. Here it is pulled out:
Here it is with the piston fully down:
I have to drop the piston below the bottom housing to get the spring to fully collapse. See:
If I remove the driver then it works perfectly. but I have to animate the shape keys separately. Which I don’t want to do:
I am 99% sure my math is wrong or a setting is wrong with the driver. Any thoughts?