Attack on Titan - Fan Game

Hi guys,

I have some trouble to understand how physics constraint works, especially the Linear Motor part. In this exemple I’m trying to find a way to link the sphere to the cube, and have a force pulling the sphere towards the cube, like a grappling hook. But as you can see in the video the Linear Motor doesn’t seem to work :

Any idea how to fix that ? Thank you in advance

You can find my set up here :