Help distance constraints

[TootsManuva]

I am new to Unity so thanks in advance for your patience folks. I have a simple physics game set up where the player moves platforms around to get a bouncing ball from one point of the "course" to another. I want to constrain the movement of these platforms by attaching a rope between them and another fixed object. The problem is that the rope will stretch forever, no matter how much I change the distance constraints, so it does not restrict the movement of the platform. I hope someone can point me in the right direction on this.

Thanks.